Zener Diode Dilemma

Discussion in 'Electrical Engineering' started by jjk, Oct 18, 2013.

  1. jjk

    jjk Guest

    Zener Diode Dilemma

    I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them before installing in a circuit I'm building.

    The diode test function on my meter shows 0.6v forward biased and .9v reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v forward biased and when reversed biased I see the same reading as not connected to the diode at all - which is what I would expect.

    Further, I inserted the diodes in a test circuit described below.

    vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.

    When vcc voltage was applied, current was measured as shown below with the diode conducting all the time, and I could never get the voltage across thezener to reach 3.3v without smoking the resistor.

    1.5v 0.1mA
    2.0v 0.6mA
    2.5v 1.1mA
    2.7v 1.5mA
    2.9v 1.7mA
    3.0v 1.8mA

    All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit the same behavior - conducting well before their breakdown voltage.

    Trying the above with a 5.6v zener shows no current flow until the voltage across the diode reached the device rated breakdown voltage. I also put a scope on the power supply to verify it was stable.

    Any guidance as to what I may be doing wrong would be appreciated.

    Thanks.
     
    jjk, Oct 18, 2013
    #1
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  2. jjk

    Tom Biasi Guest

    On 10/18/2013 8:01 AM, jjk wrote:
    > Zener Diode Dilemma
    >
    > I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them before installing in a circuit I'm building.
    >
    > The diode test function on my meter shows 0.6v forward biased and .9v reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v forward biased and when reversed biased I see the same reading as not connected to the diode at all - which is what I would expect.
    >
    > Further, I inserted the diodes in a test circuit described below.
    >
    > vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.
    >
    > When vcc voltage was applied, current was measured as shown below with the diode conducting all the time, and I could never get the voltage across the zener to reach 3.3v without smoking the resistor.
    >
    > 1.5v 0.1mA
    > 2.0v 0.6mA
    > 2.5v 1.1mA
    > 2.7v 1.5mA
    > 2.9v 1.7mA
    > 3.0v 1.8mA
    >
    > All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit the same behavior - conducting well before their breakdown voltage.
    >
    > Trying the above with a 5.6v zener shows no current flow until the voltage across the diode reached the device rated breakdown voltage. I also put a scope on the power supply to verify it was stable.
    >
    > Any guidance as to what I may be doing wrong would be appreciated.
    >
    > Thanks.
    >

    First, the diode function on your multimeter will not give you any
    useful information about zeners.
    Second, Your test looks strange. Is your supply current limiting perhaps?
     
    Tom Biasi, Oct 18, 2013
    #2
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  3. In article <>,
    jjk <> wrote:

    > Zener Diode Dilemma
    >
    > I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them
    > before installing in a circuit I'm building.
    >
    > The diode test function on my meter shows 0.6v forward biased and .9v
    > reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v
    > forward biased and when reversed biased I see the same reading as not
    > connected to the diode at all - which is what I would expect.
    >
    > Further, I inserted the diodes in a test circuit described below.
    >
    > vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to
    > ground.
    >
    > When vcc voltage was applied, current was measured as shown below with the
    > diode conducting all the time, and I could never get the voltage across the
    > zener to reach 3.3v without smoking the resistor.
    >
    > 1.5v 0.1mA
    > 2.0v 0.6mA
    > 2.5v 1.1mA
    > 2.7v 1.5mA
    > 2.9v 1.7mA
    > 3.0v 1.8mA
    >
    > All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad
    > lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit
    > the same behavior - conducting well before their breakdown voltage.
    >
    > Trying the above with a 5.6v zener shows no current flow until the voltage
    > across the diode reached the device rated breakdown voltage. I also put a
    > scope on the power supply to verify it was stable.


    JJK-

    Plotting your Voltage vs current data suggests you may be measuring the
    forward-bias curve of several diode junctions connected in series. (It
    looks more like a constant-Voltage curve than constant-current.)

    The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good
    as a diode on the diode ranges of a Fluke 8020A multimeter. I did not
    run your current vs Voltage test, but would expect it to behave as well
    as your 5.6 Volt test.

    I wonder if both your source of the 1N4728 diode and NTE, get their
    diodes from the same factory? There could have been a batch that were
    mis-labeled, or they could have fallen victim to counterfeit parts.

    Fred
     
    Fred McKenzie, Oct 20, 2013
    #3
  4. jjk

    Tom Biasi Guest

    On 10/20/2013 2:04 PM, Fred McKenzie wrote:
    > In article <>,
    > jjk <> wrote:
    >
    >> Zener Diode Dilemma
    >>
    >> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them
    >> before installing in a circuit I'm building.
    >>
    >> The diode test function on my meter shows 0.6v forward biased and .9v
    >> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v
    >> forward biased and when reversed biased I see the same reading as not
    >> connected to the diode at all - which is what I would expect.
    >>
    >> Further, I inserted the diodes in a test circuit described below.
    >>
    >> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to
    >> ground.
    >>
    >> When vcc voltage was applied, current was measured as shown below with the
    >> diode conducting all the time, and I could never get the voltage across the
    >> zener to reach 3.3v without smoking the resistor.
    >>
    >> 1.5v 0.1mA
    >> 2.0v 0.6mA
    >> 2.5v 1.1mA
    >> 2.7v 1.5mA
    >> 2.9v 1.7mA
    >> 3.0v 1.8mA
    >>
    >> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad
    >> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit
    >> the same behavior - conducting well before their breakdown voltage.
    >>
    >> Trying the above with a 5.6v zener shows no current flow until the voltage
    >> across the diode reached the device rated breakdown voltage. I also put a
    >> scope on the power supply to verify it was stable.

    >
    > JJK-
    >
    > Plotting your Voltage vs current data suggests you may be measuring the
    > forward-bias curve of several diode junctions connected in series. (It
    > looks more like a constant-Voltage curve than constant-current.)
    >
    > The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good
    > as a diode on the diode ranges of a Fluke 8020A multimeter. I did not
    > run your current vs Voltage test, but would expect it to behave as well
    > as your 5.6 Volt test.
    >
    > I wonder if both your source of the 1N4728 diode and NTE, get their
    > diodes from the same factory? There could have been a batch that were
    > mis-labeled, or they could have fallen victim to counterfeit parts.
    >
    > Fred
    >

    The curve is linear until he gets to 2.7 volts then there is a bump
    (reading error?). This looks like a forward conducting diode and the
    readings are across the resistor.
     
    Tom Biasi, Oct 20, 2013
    #4
  5. jjk

    jjk Guest

    On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:
    > On 10/20/2013 2:04 PM, Fred McKenzie wrote:
    >
    > > In article <>,

    >
    > > jjk wrote:

    >
    > >

    >
    > >> Zener Diode Dilemma

    >
    > >>

    >
    > >> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them

    >
    > >> before installing in a circuit I'm building.

    >
    > >>

    >
    > >> The diode test function on my meter shows 0.6v forward biased and .9v

    >
    > >> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >
    > >> forward biased and when reversed biased I see the same reading as not

    >
    > >> connected to the diode at all - which is what I would expect.

    >
    > >>

    >
    > >> Further, I inserted the diodes in a test circuit described below.

    >
    > >>

    >
    > >> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >
    > >> ground.

    >
    > >>

    >
    > >> When vcc voltage was applied, current was measured as shown below withthe

    >
    > >> diode conducting all the time, and I could never get the voltage across the

    >
    > >> zener to reach 3.3v without smoking the resistor.

    >
    > >>

    >
    > >> 1.5v 0.1mA

    >
    > >> 2.0v 0.6mA

    >
    > >> 2.5v 1.1mA

    >
    > >> 2.7v 1.5mA

    >
    > >> 2.9v 1.7mA

    >
    > >> 3.0v 1.8mA

    >
    > >>

    >
    > >> All of the 3.3v parts I tested exhibited the same behavior. Suspectinga bad

    >
    > >> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >
    > >> the same behavior - conducting well before their breakdown voltage.

    >
    > >>

    >
    > >> Trying the above with a 5.6v zener shows no current flow until the voltage

    >
    > >> across the diode reached the device rated breakdown voltage. I also put a

    >
    > >> scope on the power supply to verify it was stable.

    >
    > >

    >
    > > JJK-

    >
    > >

    >
    > > Plotting your Voltage vs current data suggests you may be measuring the

    >
    > > forward-bias curve of several diode junctions connected in series. (It

    >
    > > looks more like a constant-Voltage curve than constant-current.)

    >
    > >

    >
    > > The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good

    >
    > > as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >
    > > run your current vs Voltage test, but would expect it to behave as well

    >
    > > as your 5.6 Volt test.

    >
    > >

    >
    > > I wonder if both your source of the 1N4728 diode and NTE, get their

    >
    > > diodes from the same factory? There could have been a batch that were

    >
    > > mis-labeled, or they could have fallen victim to counterfeit parts.

    >
    > >

    >
    > > Fred

    >
    > >

    >
    > The curve is linear until he gets to 2.7 volts then there is a bump
    >
    > (reading error?). This looks like a forward conducting diode and the
    >
    > readings are across the resistor.



    Thanks to all who replied.
    There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part worksas expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.
    330 ohm resistor measures 327 ohms

    1N4728A 3.3v 1W Zener diode

    Iz
    vcc (mA) Vzener
    1.5 0.2 1.42
    2.0 0.8 1.72
    2.5 1.7 1.91
    3.0 2.8 2.05
    3.5 4.1 2.16
    4.0 5.3 2.24
    4.5 6.6 2.3
    5.0 8.0 2.37
    5.5 9.4 2.43
    6.0 10.8 2.48
    7.0 13.6 2.56
    8.0 16.5 2.62
    9.0 19.4 2.69
    10.0 22.4 2.73
    20.0 55.2 3.1
    25.0 71.3 3.3


    1N752 5.6v zener diode

    Iz
    vcc (mA) Vzener
    1.5 0 1.5
    .... ... ...
    4.0 0 4.0
    4.5 0 4.49
    5.0 .1 5.0
    5.5 .2 5.43
    6.0 1.0 5.67
     
    jjk, Oct 22, 2013
    #5
  6. jjk

    JW Guest

    On Tue, 22 Oct 2013 05:59:52 -0700 (PDT) jjk <> wrote in
    Message id: <>:

    >Thanks to all who replied.
    >There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)
    >
    >vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.
    >330 ohm resistor measures 327 ohms
    >
    >1N4728A 3.3v 1W Zener diode
    >
    > Iz
    >vcc (mA) Vzener
    >1.5 0.2 1.42
    >2.0 0.8 1.72
    >2.5 1.7 1.91
    >3.0 2.8 2.05
    >3.5 4.1 2.16
    >4.0 5.3 2.24
    >4.5 6.6 2.3
    >5.0 8.0 2.37
    >5.5 9.4 2.43
    >6.0 10.8 2.48
    >7.0 13.6 2.56
    >8.0 16.5 2.62
    >9.0 19.4 2.69
    >10.0 22.4 2.73
    >20.0 55.2 3.1
    >25.0 71.3 3.3


    Where are you getting these diodes?
     
    JW, Oct 22, 2013
    #6
  7. jjk

    Tom Biasi Guest

    On 10/22/2013 8:59 AM, jjk wrote:
    > On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:
    >> On 10/20/2013 2:04 PM, Fred McKenzie wrote:
    >>
    >>> In article <>,

    >>
    >>> jjk wrote:

    >>
    >>>

    >>
    >>>> Zener Diode Dilemma

    >>
    >>>>

    >>
    >>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them

    >>
    >>>> before installing in a circuit I'm building.

    >>
    >>>>

    >>
    >>>> The diode test function on my meter shows 0.6v forward biased and .9v

    >>
    >>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >>
    >>>> forward biased and when reversed biased I see the same reading as not

    >>
    >>>> connected to the diode at all - which is what I would expect.

    >>
    >>>>

    >>
    >>>> Further, I inserted the diodes in a test circuit described below.

    >>
    >>>>

    >>
    >>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >>
    >>>> ground.

    >>
    >>>>

    >>
    >>>> When vcc voltage was applied, current was measured as shown below with the

    >>
    >>>> diode conducting all the time, and I could never get the voltage across the

    >>
    >>>> zener to reach 3.3v without smoking the resistor.

    >>
    >>>>

    >>
    >>>> 1.5v 0.1mA

    >>
    >>>> 2.0v 0.6mA

    >>
    >>>> 2.5v 1.1mA

    >>
    >>>> 2.7v 1.5mA

    >>
    >>>> 2.9v 1.7mA

    >>
    >>>> 3.0v 1.8mA

    >>
    >>>>

    >>
    >>>> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad

    >>
    >>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >>
    >>>> the same behavior - conducting well before their breakdown voltage.

    >>
    >>>>

    >>
    >>>> Trying the above with a 5.6v zener shows no current flow until the voltage

    >>
    >>>> across the diode reached the device rated breakdown voltage. I also put a

    >>
    >>>> scope on the power supply to verify it was stable.

    >>
    >>>

    >>
    >>> JJK-

    >>
    >>>

    >>
    >>> Plotting your Voltage vs current data suggests you may be measuring the

    >>
    >>> forward-bias curve of several diode junctions connected in series. (It

    >>
    >>> looks more like a constant-Voltage curve than constant-current.)

    >>
    >>>

    >>
    >>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good

    >>
    >>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >>
    >>> run your current vs Voltage test, but would expect it to behave as well

    >>
    >>> as your 5.6 Volt test.

    >>
    >>>

    >>
    >>> I wonder if both your source of the 1N4728 diode and NTE, get their

    >>
    >>> diodes from the same factory? There could have been a batch that were

    >>
    >>> mis-labeled, or they could have fallen victim to counterfeit parts.

    >>
    >>>

    >>
    >>> Fred

    >>
    >>>

    >>
    >> The curve is linear until he gets to 2.7 volts then there is a bump
    >>
    >> (reading error?). This looks like a forward conducting diode and the
    >>
    >> readings are across the resistor.

    >
    >
    > Thanks to all who replied.
    > There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)
    >
    > vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.
    > 330 ohm resistor measures 327 ohms
    >
    > 1N4728A 3.3v 1W Zener diode
    >
    > Iz
    > vcc (mA) Vzener
    > 1.5 0.2 1.42
    > 2.0 0.8 1.72
    > 2.5 1.7 1.91
    > 3.0 2.8 2.05
    > 3.5 4.1 2.16
    > 4.0 5.3 2.24
    > 4.5 6.6 2.3
    > 5.0 8.0 2.37
    > 5.5 9.4 2.43
    > 6.0 10.8 2.48
    > 7.0 13.6 2.56
    > 8.0 16.5 2.62
    > 9.0 19.4 2.69
    > 10.0 22.4 2.73
    > 20.0 55.2 3.1
    > 25.0 71.3 3.3
    >
    >
    > 1N752 5.6v zener diode
    >
    > Iz
    > vcc (mA) Vzener
    > 1.5 0 1.5
    > ... ... ...
    > 4.0 0 4.0
    > 4.5 0 4.49
    > 5.0 .1 5.0
    > 5.5 .2 5.43
    > 6.0 1.0 5.67
    >
    >

    Do you have a different power supply to try?
     
    Tom Biasi, Oct 22, 2013
    #7
  8. jjk

    jjk Guest

    On Tuesday, October 22, 2013 10:50:17 AM UTC-4, JW wrote:
    > On Tue, 22 Oct 2013 05:59:52 -0700 (PDT) jjk wrote in
    >
    > Message id: <>:
    >
    >
    >
    > >Thanks to all who replied.

    >
    > >There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >
    > >

    >
    > >vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.

    >
    > >330 ohm resistor measures 327 ohms

    >
    > >

    >
    > >1N4728A 3.3v 1W Zener diode

    >
    > >

    >
    > > Iz

    >
    > >vcc (mA) Vzener

    >
    > >1.5 0.2 1.42

    >
    > >2.0 0.8 1.72

    >
    > >2.5 1.7 1.91

    >
    > >3.0 2.8 2.05

    >
    > >3.5 4.1 2.16

    >
    > >4.0 5.3 2.24

    >
    > >4.5 6.6 2.3

    >
    > >5.0 8.0 2.37

    >
    > >5.5 9.4 2.43

    >
    > >6.0 10.8 2.48

    >
    > >7.0 13.6 2.56

    >
    > >8.0 16.5 2.62

    >
    > >9.0 19.4 2.69

    >
    > >10.0 22.4 2.73

    >
    > >20.0 55.2 3.1

    >
    > >25.0 71.3 3.3

    >
    >
    >
    > Where are you getting these diodes?


    I received a package of 50 Fairchild devices from Jameco.com.
    Then I purchased 5 NTE devices from a local electronics store.
    All of the ones I have tested from the above failed.
    I contacted Jameco and they sent 50 replacements and all that I tested failed in the same way. I've been in contact with the Jameco technical rep and they are looking into this and trying to obtain devices from another lot from their supplier.
     
    jjk, Oct 23, 2013
    #8
  9. jjk

    jjk Guest

    On Tuesday, October 22, 2013 11:12:24 AM UTC-4, Tom Biasi wrote:
    > On 10/22/2013 8:59 AM, jjk wrote:
    >
    > > On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:

    >
    > >> On 10/20/2013 2:04 PM, Fred McKenzie wrote:

    >
    > >>

    >
    > >>> In article <>,

    >
    > >>

    >
    > >>> jjk wrote:

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>>> Zener Diode Dilemma

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to testthem

    >
    > >>

    >
    > >>>> before installing in a circuit I'm building.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> The diode test function on my meter shows 0.6v forward biased and .9v

    >
    > >>

    >
    > >>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >
    > >>

    >
    > >>>> forward biased and when reversed biased I see the same reading as not

    >
    > >>

    >
    > >>>> connected to the diode at all - which is what I would expect.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> Further, I inserted the diodes in a test circuit described below.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >
    > >>

    >
    > >>>> ground.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> When vcc voltage was applied, current was measured as shown below with the

    >
    > >>

    >
    > >>>> diode conducting all the time, and I could never get the voltage across the

    >
    > >>

    >
    > >>>> zener to reach 3.3v without smoking the resistor.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> 1.5v 0.1mA

    >
    > >>

    >
    > >>>> 2.0v 0.6mA

    >
    > >>

    >
    > >>>> 2.5v 1.1mA

    >
    > >>

    >
    > >>>> 2.7v 1.5mA

    >
    > >>

    >
    > >>>> 2.9v 1.7mA

    >
    > >>

    >
    > >>>> 3.0v 1.8mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad

    >
    > >>

    >
    > >>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >
    > >>

    >
    > >>>> the same behavior - conducting well before their breakdown voltage.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> Trying the above with a 5.6v zener shows no current flow until the voltage

    >
    > >>

    >
    > >>>> across the diode reached the device rated breakdown voltage. I also put a

    >
    > >>

    >
    > >>>> scope on the power supply to verify it was stable.

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> JJK-

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> Plotting your Voltage vs current data suggests you may be measuring the

    >
    > >>

    >
    > >>> forward-bias curve of several diode junctions connected in series. (It

    >
    > >>

    >
    > >>> looks more like a constant-Voltage curve than constant-current.)

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good

    >
    > >>

    >
    > >>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >
    > >>

    >
    > >>> run your current vs Voltage test, but would expect it to behave as well

    >
    > >>

    >
    > >>> as your 5.6 Volt test.

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> I wonder if both your source of the 1N4728 diode and NTE, get their

    >
    > >>

    >
    > >>> diodes from the same factory? There could have been a batch that were

    >
    > >>

    >
    > >>> mis-labeled, or they could have fallen victim to counterfeit parts.

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> Fred

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >> The curve is linear until he gets to 2.7 volts then there is a bump

    >
    > >>

    >
    > >> (reading error?). This looks like a forward conducting diode and the

    >
    > >>

    >
    > >> readings are across the resistor.

    >
    > >

    >
    > >

    >
    > > Thanks to all who replied.

    >
    > > There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >
    > >

    >
    > > vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anodeto ground.

    >
    > > 330 ohm resistor measures 327 ohms

    >
    > >

    >
    > > 1N4728A 3.3v 1W Zener diode

    >
    > >

    >
    > > Iz

    >
    > > vcc (mA) Vzener

    >
    > > 1.5 0.2 1.42

    >
    > > 2.0 0.8 1.72

    >
    > > 2.5 1.7 1.91

    >
    > > 3.0 2.8 2.05

    >
    > > 3.5 4.1 2.16

    >
    > > 4.0 5.3 2.24

    >
    > > 4.5 6.6 2.3

    >
    > > 5.0 8.0 2.37

    >
    > > 5.5 9.4 2.43

    >
    > > 6.0 10.8 2.48

    >
    > > 7.0 13.6 2.56

    >
    > > 8.0 16.5 2.62

    >
    > > 9.0 19.4 2.69

    >
    > > 10.0 22.4 2.73

    >
    > > 20.0 55.2 3.1

    >
    > > 25.0 71.3 3.3

    >
    > >

    >
    > >

    >
    > > 1N752 5.6v zener diode

    >
    > >

    >
    > > Iz

    >
    > > vcc (mA) Vzener

    >
    > > 1.5 0 1.5

    >
    > > ... ... ...

    >
    > > 4.0 0 4.0

    >
    > > 4.5 0 4.49

    >
    > > 5.0 .1 5.0

    >
    > > 5.5 .2 5.43

    >
    > > 6.0 1.0 5.67

    >
    > >

    >
    > >

    >
    > Do you have a different power supply to try?


    I also tried a 9v battery connected to a 100K pot, wiper connected to a 10kresistor to the zener cathode, and the anode connected to the other end ofthe pot and to the battery negative post.

    +9v
    |
    100K pot ---10K ----cathode
    | |
    gnd------------------|

    Works fine with all of my 5.x zeners.
    The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is aat 9.2v.

    This feels like a bad dream where you run and not get anywhere.
    I sure would like to get this behind me and continue with the larger project I'm working on.
     
    jjk, Oct 23, 2013
    #9
  10. In article <>,
    jjk <> wrote:

    > I also tried a 9v battery connected to a 100K pot, wiper connected to a 10k
    > resistor to the zener cathode, and the anode connected to the other end of
    > the pot and to the battery negative post.
    >
    > +9v
    > |
    > 100K pot ---10K ----cathode
    > | |
    > gnd------------------|
    >
    > Works fine with all of my 5.x zeners.
    > The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is a
    > at 9.2v.
    >
    > This feels like a bad dream where you run and not get anywhere.
    > I sure would like to get this behind me and continue with the larger project
    > I'm working on.


    JJK-

    I did not see how you were using the 3.3 V Zeners. If you are
    generating 3.3 Volt power, you might consider using the LM-317. They
    are available in several packages including surface mount, and can be
    adjusted from 1.2 to 39 Volts using a pair of resistors.

    Fred
     
    Fred McKenzie, Oct 24, 2013
    #10
  11. jjk

    Tom Biasi Guest

    On 10/23/2013 6:52 PM, jjk wrote:
    > On Tuesday, October 22, 2013 11:12:24 AM UTC-4, Tom Biasi wrote:
    >> On 10/22/2013 8:59 AM, jjk wrote:
    >>
    >>> On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:

    >>
    >>>> On 10/20/2013 2:04 PM, Fred McKenzie wrote:

    >>
    >>>>

    >>
    >>>>> In article <>,

    >>
    >>>>

    >>
    >>>>> jjk wrote:

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>>> Zener Diode Dilemma

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them

    >>
    >>>>

    >>
    >>>>>> before installing in a circuit I'm building.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> The diode test function on my meter shows 0.6v forward biased and .9v

    >>
    >>>>

    >>
    >>>>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >>
    >>>>

    >>
    >>>>>> forward biased and when reversed biased I see the same reading as not

    >>
    >>>>

    >>
    >>>>>> connected to the diode at all - which is what I would expect.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> Further, I inserted the diodes in a test circuit described below.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >>
    >>>>

    >>
    >>>>>> ground.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> When vcc voltage was applied, current was measured as shown below with the

    >>
    >>>>

    >>
    >>>>>> diode conducting all the time, and I could never get the voltage across the

    >>
    >>>>

    >>
    >>>>>> zener to reach 3.3v without smoking the resistor.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> 1.5v 0.1mA

    >>
    >>>>

    >>
    >>>>>> 2.0v 0.6mA

    >>
    >>>>

    >>
    >>>>>> 2.5v 1.1mA

    >>
    >>>>

    >>
    >>>>>> 2.7v 1.5mA

    >>
    >>>>

    >>
    >>>>>> 2.9v 1.7mA

    >>
    >>>>

    >>
    >>>>>> 3.0v 1.8mA

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad

    >>
    >>>>

    >>
    >>>>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >>
    >>>>

    >>
    >>>>>> the same behavior - conducting well before their breakdown voltage.

    >>
    >>>>

    >>
    >>>>>>

    >>
    >>>>

    >>
    >>>>>> Trying the above with a 5.6v zener shows no current flow until the voltage

    >>
    >>>>

    >>
    >>>>>> across the diode reached the device rated breakdown voltage. I also put a

    >>
    >>>>

    >>
    >>>>>> scope on the power supply to verify it was stable.

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>> JJK-

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>> Plotting your Voltage vs current data suggests you may be measuring the

    >>
    >>>>

    >>
    >>>>> forward-bias curve of several diode junctions connected in series. (It

    >>
    >>>>

    >>
    >>>>> looks more like a constant-Voltage curve than constant-current.)

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good

    >>
    >>>>

    >>
    >>>>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >>
    >>>>

    >>
    >>>>> run your current vs Voltage test, but would expect it to behave as well

    >>
    >>>>

    >>
    >>>>> as your 5.6 Volt test.

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>> I wonder if both your source of the 1N4728 diode and NTE, get their

    >>
    >>>>

    >>
    >>>>> diodes from the same factory? There could have been a batch that were

    >>
    >>>>

    >>
    >>>>> mis-labeled, or they could have fallen victim to counterfeit parts.

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>>> Fred

    >>
    >>>>

    >>
    >>>>>

    >>
    >>>>

    >>
    >>>> The curve is linear until he gets to 2.7 volts then there is a bump

    >>
    >>>>

    >>
    >>>> (reading error?). This looks like a forward conducting diode and the

    >>
    >>>>

    >>
    >>>> readings are across the resistor.

    >>
    >>>

    >>
    >>>

    >>
    >>> Thanks to all who replied.

    >>
    >>> There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >>
    >>>

    >>
    >>> vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.

    >>
    >>> 330 ohm resistor measures 327 ohms

    >>
    >>>

    >>
    >>> 1N4728A 3.3v 1W Zener diode

    >>
    >>>

    >>
    >>> Iz

    >>
    >>> vcc (mA) Vzener

    >>
    >>> 1.5 0.2 1.42

    >>
    >>> 2.0 0.8 1.72

    >>
    >>> 2.5 1.7 1.91

    >>
    >>> 3.0 2.8 2.05

    >>
    >>> 3.5 4.1 2.16

    >>
    >>> 4.0 5.3 2.24

    >>
    >>> 4.5 6.6 2.3

    >>
    >>> 5.0 8.0 2.37

    >>
    >>> 5.5 9.4 2.43

    >>
    >>> 6.0 10.8 2.48

    >>
    >>> 7.0 13.6 2.56

    >>
    >>> 8.0 16.5 2.62

    >>
    >>> 9.0 19.4 2.69

    >>
    >>> 10.0 22.4 2.73

    >>
    >>> 20.0 55.2 3.1

    >>
    >>> 25.0 71.3 3.3

    >>
    >>>

    >>
    >>>

    >>
    >>> 1N752 5.6v zener diode

    >>
    >>>

    >>
    >>> Iz

    >>
    >>> vcc (mA) Vzener

    >>
    >>> 1.5 0 1.5

    >>
    >>> ... ... ...

    >>
    >>> 4.0 0 4.0

    >>
    >>> 4.5 0 4.49

    >>
    >>> 5.0 .1 5.0

    >>
    >>> 5.5 .2 5.43

    >>
    >>> 6.0 1.0 5.67

    >>
    >>>

    >>
    >>>

    >>
    >> Do you have a different power supply to try?

    >
    > I also tried a 9v battery connected to a 100K pot, wiper connected to a 10k resistor to the zener cathode, and the anode connected to the other end of the pot and to the battery negative post.
    >
    > +9v
    > |
    > 100K pot ---10K ----cathode
    > | |
    > gnd------------------|
    >
    > Works fine with all of my 5.x zeners.
    > The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is a at 9.2v.
    >
    > This feels like a bad dream where you run and not get anywhere.
    > I sure would like to get this behind me and continue with the larger project I'm working on.
    >
    >
    >
    >
    >
    >
    >

    It is not likely that you are receiving so many defective parts. I
    suggested a different power supply, now I suggest a different meter.
    I do this only to eliminate the possible variables. The next is to
    eliminate you. I mean give them to someone else to test. Please don't be
    insulted.

    Tom
     
    Tom Biasi, Oct 24, 2013
    #11
  12. jjk

    jjk Guest

    On Wednesday, October 23, 2013 8:39:08 PM UTC-4, Fred McKenzie wrote:
    > In article <>,
    >
    > jjk wrote:
    >
    >
    >
    > > I also tried a 9v battery connected to a 100K pot, wiper connected to a 10k

    >
    > > resistor to the zener cathode, and the anode connected to the other end of

    >
    > > the pot and to the battery negative post.

    >
    > >

    >
    > > +9v

    >
    > > |

    >
    > > 100K pot ---10K ----cathode

    >
    > > | |

    >
    > > gnd------------------|

    >
    > >

    >
    > > Works fine with all of my 5.x zeners.

    >
    > > The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is a

    >
    > > at 9.2v.

    >
    > >

    >
    > > This feels like a bad dream where you run and not get anywhere.

    >
    > > I sure would like to get this behind me and continue with the larger project

    >
    > > I'm working on.

    >
    >
    >
    > JJK-
    >
    >
    >
    > I did not see how you were using the 3.3 V Zeners. If you are
    >
    > generating 3.3 Volt power, you might consider using the LM-317. They
    >
    > are available in several packages including surface mount, and can be
    >
    > adjusted from 1.2 to 39 Volts using a pair of resistors.
    >
    >
    >
    > Fred


    Thanks for your comments. The potentiometer circuit I described was for testing an alternate power supply source to rule out a problem with my bench supply.
    I intend to use the zener for over voltage pin protection on 3.3v devices.
     
    jjk, Oct 24, 2013
    #12
  13. jjk

    jjk Guest

    On Wednesday, October 23, 2013 10:34:04 PM UTC-4, Tom Biasi wrote:
    > On 10/23/2013 6:52 PM, jjk wrote:
    >
    > > On Tuesday, October 22, 2013 11:12:24 AM UTC-4, Tom Biasi wrote:

    >
    > >> On 10/22/2013 8:59 AM, jjk wrote:

    >
    > >>

    >
    > >>> On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:

    >
    > >>

    >
    > >>>> On 10/20/2013 2:04 PM, Fred McKenzie wrote:

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> In article <>,

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> jjk wrote:

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> Zener Diode Dilemma

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> before installing in a circuit I'm building.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> The diode test function on my meter shows 0.6v forward biased and ..9v

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> forward biased and when reversed biased I see the same reading as not

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> connected to the diode at all - which is what I would expect.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> Further, I inserted the diodes in a test circuit described below.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> ground.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> When vcc voltage was applied, current was measured as shown below with the

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> diode conducting all the time, and I could never get the voltage across the

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> zener to reach 3.3v without smoking the resistor.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 1.5v 0.1mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 2.0v 0.6mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 2.5v 1.1mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 2.7v 1.5mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 2.9v 1.7mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> 3.0v 1.8mA

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> the same behavior - conducting well before their breakdown voltage..

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> Trying the above with a 5.6v zener shows no current flow until thevoltage

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> across the diode reached the device rated breakdown voltage. I also put a

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>> scope on the power supply to verify it was stable.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> JJK-

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> Plotting your Voltage vs current data suggests you may be measuringthe

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> forward-bias curve of several diode junctions connected in series. (It

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> looks more like a constant-Voltage curve than constant-current.)

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> run your current vs Voltage test, but would expect it to behave as well

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> as your 5.6 Volt test.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> I wonder if both your source of the 1N4728 diode and NTE, get their

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> diodes from the same factory? There could have been a batch that were

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> mis-labeled, or they could have fallen victim to counterfeit parts.

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>> Fred

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>>>

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> The curve is linear until he gets to 2.7 volts then there is a bump

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> (reading error?). This looks like a forward conducting diode and the

    >
    > >>

    >
    > >>>>

    >
    > >>

    >
    > >>>> readings are across the resistor.

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> Thanks to all who replied.

    >
    > >>

    >
    > >>> There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v partworks as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.

    >
    > >>

    >
    > >>> 330 ohm resistor measures 327 ohms

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> 1N4728A 3.3v 1W Zener diode

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> Iz

    >
    > >>

    >
    > >>> vcc (mA) Vzener

    >
    > >>

    >
    > >>> 1.5 0.2 1.42

    >
    > >>

    >
    > >>> 2.0 0.8 1.72

    >
    > >>

    >
    > >>> 2.5 1.7 1.91

    >
    > >>

    >
    > >>> 3.0 2.8 2.05

    >
    > >>

    >
    > >>> 3.5 4.1 2.16

    >
    > >>

    >
    > >>> 4.0 5.3 2.24

    >
    > >>

    >
    > >>> 4.5 6.6 2.3

    >
    > >>

    >
    > >>> 5.0 8.0 2.37

    >
    > >>

    >
    > >>> 5.5 9.4 2.43

    >
    > >>

    >
    > >>> 6.0 10.8 2.48

    >
    > >>

    >
    > >>> 7.0 13.6 2.56

    >
    > >>

    >
    > >>> 8.0 16.5 2.62

    >
    > >>

    >
    > >>> 9.0 19.4 2.69

    >
    > >>

    >
    > >>> 10.0 22.4 2.73

    >
    > >>

    >
    > >>> 20.0 55.2 3.1

    >
    > >>

    >
    > >>> 25.0 71.3 3.3

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> 1N752 5.6v zener diode

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>> Iz

    >
    > >>

    >
    > >>> vcc (mA) Vzener

    >
    > >>

    >
    > >>> 1.5 0 1.5

    >
    > >>

    >
    > >>> ... ... ...

    >
    > >>

    >
    > >>> 4.0 0 4.0

    >
    > >>

    >
    > >>> 4.5 0 4.49

    >
    > >>

    >
    > >>> 5.0 .1 5.0

    >
    > >>

    >
    > >>> 5.5 .2 5.43

    >
    > >>

    >
    > >>> 6.0 1.0 5.67

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >>>

    >
    > >>

    >
    > >> Do you have a different power supply to try?

    >
    > >

    >
    > > I also tried a 9v battery connected to a 100K pot, wiper connected to a10k resistor to the zener cathode, and the anode connected to the other end of the pot and to the battery negative post.

    >
    > >

    >
    > > +9v

    >
    > > |

    >
    > > 100K pot ---10K ----cathode

    >
    > > | |

    >
    > > gnd------------------|

    >
    > >

    >
    > > Works fine with all of my 5.x zeners.

    >
    > > The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is a at 9.2v.

    >
    > >

    >
    > > This feels like a bad dream where you run and not get anywhere.

    >
    > > I sure would like to get this behind me and continue with the larger project I'm working on.

    >
    > >

    >
    > >

    >
    > >

    >
    > >

    >
    > >

    >
    > >

    >
    > >

    >
    > It is not likely that you are receiving so many defective parts. I
    >
    > suggested a different power supply, now I suggest a different meter.
    >
    > I do this only to eliminate the possible variables. The next is to
    >
    > eliminate you. I mean give them to someone else to test. Please don't be
    >
    > insulted.
    >
    >
    >
    > Tom


    Tom, LOL. No insult taken. I got a chuckle from your process of eliminationcomment.

    I agree having that many failures is suspect and is why I posted to this group for possible help. I tried 3 meters and 2 power supplies. In every caseall of my 5.* volt zeners work perfectly as expected. All I do is swap outthe 5v zener for the 3.3v device and see the problem. I even reversed thedirection of the 3.3v zener thinking the cathode may have been marked incorrectly. The voltage at the anode in this case is an expected 0.6v.

    If anyone reading this group would like to test a few of these, please sendme an email at jjk439 at gmail dot com and I would be glad to send them toyou.
     
    jjk, Oct 24, 2013
    #13
  14. jjk

    jjk Guest

    On Thursday, October 24, 2013 7:40:10 AM UTC-4, jjk wrote:
    > On Wednesday, October 23, 2013 10:34:04 PM UTC-4, Tom Biasi wrote:
    >
    > > On 10/23/2013 6:52 PM, jjk wrote:

    >
    > >

    >
    > > > On Tuesday, October 22, 2013 11:12:24 AM UTC-4, Tom Biasi wrote:

    >
    > >

    >
    > > >> On 10/22/2013 8:59 AM, jjk wrote:

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>> On 10/20/2013 2:04 PM, Fred McKenzie wrote:

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> In article <>,

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> jjk wrote:

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> Zener Diode Dilemma

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test them

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> before installing in a circuit I'm building.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> The diode test function on my meter shows 0.6v forward biased and .9v

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> forward biased and when reversed biased I see the same reading as not

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> connected to the diode at all - which is what I would expect.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> Further, I inserted the diodes in a test circuit described below..

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener anode to

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> ground.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> When vcc voltage was applied, current was measured as shown below with the

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> diode conducting all the time, and I could never get the voltageacross the

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> zener to reach 3.3v without smoking the resistor.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 1.5v 0.1mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 2.0v 0.6mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 2.5v 1.1mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 2.7v 1.5mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 2.9v 1.7mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> 3.0v 1.8mA

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> All of the 3.3v parts I tested exhibited the same behavior. Suspecting a bad

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too exhibit

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> the same behavior - conducting well before their breakdown voltage.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> Trying the above with a 5.6v zener shows no current flow until the voltage

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> across the diode reached the device rated breakdown voltage. I also put a

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>> scope on the power supply to verify it was stable.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> JJK-

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> Plotting your Voltage vs current data suggests you may be measuring the

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> forward-bias curve of several diode junctions connected in series.. (It

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> looks more like a constant-Voltage curve than constant-current.)

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checksgood

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> run your current vs Voltage test, but would expect it to behave as well

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> as your 5.6 Volt test.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> I wonder if both your source of the 1N4728 diode and NTE, get their

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> diodes from the same factory? There could have been a batch thatwere

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> mis-labeled, or they could have fallen victim to counterfeit parts.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>> Fred

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>> The curve is linear until he gets to 2.7 volts then there is a bump

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>> (reading error?). This looks like a forward conducting diode and the

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>> readings are across the resistor.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> Thanks to all who replied.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I hadto raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 330 ohm resistor measures 327 ohms

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 1N4728A 3.3v 1W Zener diode

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> Iz

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> vcc (mA) Vzener

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 1.5 0.2 1.42

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 2.0 0.8 1.72

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 2.5 1.7 1.91

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 3.0 2.8 2.05

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 3.5 4.1 2.16

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 4.0 5.3 2.24

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 4.5 6.6 2.3

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 5.0 8.0 2.37

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 5.5 9.4 2.43

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 6.0 10.8 2.48

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 7.0 13.6 2.56

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 8.0 16.5 2.62

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 9.0 19.4 2.69

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 10.0 22.4 2.73

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 20.0 55.2 3.1

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 25.0 71.3 3.3

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 1N752 5.6v zener diode

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> Iz

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> vcc (mA) Vzener

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 1.5 0 1.5

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> ... ... ...

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 4.0 0 4.0

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 4.5 0 4.49

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 5.0 .1 5.0

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 5.5 .2 5.43

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>> 6.0 1.0 5.67

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >>>

    >
    > >

    >
    > > >>

    >
    > >

    >
    > > >> Do you have a different power supply to try?

    >
    > >

    >
    > > >

    >
    > >

    >
    > > > I also tried a 9v battery connected to a 100K pot, wiper connected toa 10k resistor to the zener cathode, and the anode connected to the other end of the pot and to the battery negative post.

    >
    > >

    >
    > > >

    >
    > >

    >
    > > > +9v

    >
    > >

    >
    > > > |

    >
    > >

    >
    > > > 100K pot ---10K ----cathode

    >
    > >

    >
    > > > | |

    >
    > >

    >
    > > > gnd------------------|

    >
    > >

    >
    > > >

    >
    > >

    >
    > > > Works fine with all of my 5.x zeners.

    >
    > >

    >
    > > > The 3.3v zeners never get above 1.8v at the cathode when the pot wiper is a at 9.2v.

    >
    > >

    >
    > > >

    >
    > >

    >
    > > > This feels like a bad dream where you run and not get anywhere.

    >
    > >

    >
    > > > I sure would like to get this behind me and continue with the larger project I'm working on.

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > >

    >
    > >

    >
    > > It is not likely that you are receiving so many defective parts. I

    >
    > >

    >
    > > suggested a different power supply, now I suggest a different meter.

    >
    > >

    >
    > > I do this only to eliminate the possible variables. The next is to

    >
    > >

    >
    > > eliminate you. I mean give them to someone else to test. Please don't be

    >
    > >

    >
    > > insulted.

    >
    > >

    >
    > >

    >
    > >

    >
    > > Tom

    >
    >
    >
    > Tom, LOL. No insult taken. I got a chuckle from your process of elimination comment.
    >
    >
    >
    > I agree having that many failures is suspect and is why I posted to this group for possible help. I tried 3 meters and 2 power supplies. In every case all of my 5.* volt zeners work perfectly as expected. All I do is swap out the 5v zener for the 3.3v device and see the problem. I even reversed the direction of the 3.3v zener thinking the cathode may have been marked incorrectly. The voltage at the anode in this case is an expected 0.6v.
    >
    >
    >
    > If anyone reading this group would like to test a few of these, please send me an email at jjk439 at gmail dot com and I would be glad to send them to you.


    I am now relieved that my sanity on this issue is intact, but still frustrated at not being able to find any functional zener diodes. I received a phone call from a tech at Jameco Electronics stating they took delivery of another 50 3.3v zener diodes, and they all failed their tests the same way they failed mine.
    They concur there is a problem with these devices.

    Thanks to all who replied to my post.
     
    jjk, Oct 30, 2013
    #14
  15. jjk

    Tom Biasi Guest

    On 10/30/2013 2:04 PM, jjk wrote:

    > I am now relieved that my sanity on this issue is intact, but still frustrated at not being able to find any functional zener diodes. I received a phone
    > call from a tech at Jameco Electronics stating they took delivery of another 50 3.3v zener diodes, and they all failed their tests the same way they
    > failed mine.
    > They concur there is a problem with these devices.
    >
    > Thanks to all who replied to my post.
    >
    >

    I guess Jameco doesn't have any incoming QA inspection.
     
    Tom Biasi, Oct 31, 2013
    #15
  16. In article <>,
    jjk <> writes:
    > There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)
    > vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode to ground.
    > 330 ohm resistor measures 327 ohms
    > 1N4728A 3.3v 1W Zener diode
    > Iz
    > vcc (mA) Vzener
    > 1.5 0.2 1.42
    > 2.0 0.8 1.72
    > 2.5 1.7 1.91
    > 3.0 2.8 2.05
    > 3.5 4.1 2.16
    > 4.0 5.3 2.24
    > 4.5 6.6 2.3
    > 5.0 8.0 2.37
    > 5.5 9.4 2.43
    > 6.0 10.8 2.48
    > 7.0 13.6 2.56
    > 8.0 16.5 2.62
    > 9.0 19.4 2.69
    > 10.0 22.4 2.73
    > 20.0 55.2 3.1
    > 25.0 71.3 3.3


    This exactly matches the datasheet, which says it needs at least 76mA
    in order to act as a zener voltage reference.

    This is a common issue with low voltage zeners - the current they
    need to operate is high (compared with higher voltage zeners).

    If you want a low voltage reference at low current (e.g. for battery
    operated equipment), an LED can often be used (forward biased) at a
    much lower operating current (1mA or less), although not quite as
    stable a reference.

    --
    Andrew Gabriel
    [email address is not usable -- followup in the newsgroup]
     
    Andrew Gabriel, Oct 31, 2013
    #16
  17. jjk

    jjk Guest

    On Thursday, October 31, 2013 4:42:08 PM UTC-4, Andrew Gabriel wrote:
    > In article <>,
    >
    > jjk writes:
    >
    > > There is definitely very wrong. I just took delivery of 50 Fairchild replacement zeners and reran my tests to verify, this time using a 330 ohm resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part works as expected and doesn't conduct until the avalanche voltage is approached whereas the 3.3v part is still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at the cathode, then the magic smoke came out of the resistor. :)

    >
    > > vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anodeto ground.

    >
    > > 330 ohm resistor measures 327 ohms

    >
    > > 1N4728A 3.3v 1W Zener diode

    >
    > > Iz

    >
    > > vcc (mA) Vzener

    >
    > > 1.5 0.2 1.42

    >
    > > 2.0 0.8 1.72

    >
    > > 2.5 1.7 1.91

    >
    > > 3.0 2.8 2.05

    >
    > > 3.5 4.1 2.16

    >
    > > 4.0 5.3 2.24

    >
    > > 4.5 6.6 2.3

    >
    > > 5.0 8.0 2.37

    >
    > > 5.5 9.4 2.43

    >
    > > 6.0 10.8 2.48

    >
    > > 7.0 13.6 2.56

    >
    > > 8.0 16.5 2.62

    >
    > > 9.0 19.4 2.69

    >
    > > 10.0 22.4 2.73

    >
    > > 20.0 55.2 3.1

    >
    > > 25.0 71.3 3.3

    >
    >
    >
    > This exactly matches the datasheet, which says it needs at least 76mA
    >
    > in order to act as a zener voltage reference.
    >
    >
    >
    > This is a common issue with low voltage zeners - the current they
    >
    > need to operate is high (compared with higher voltage zeners).
    >
    >
    >
    > If you want a low voltage reference at low current (e.g. for battery
    >
    > operated equipment), an LED can often be used (forward biased) at a
    >
    > much lower operating current (1mA or less), although not quite as
    >
    > stable a reference.
    >
    >
    >
    > --
    >
    > Andrew Gabriel
    >
    > [email address is not usable -- followup in the newsgroup]


    Thanks for your comments Andrew.
    I'm wondering why the zener would conduct at all at voltages as low as 1.4v?
    My goal was not to use the zener as a regulator, but to protect 3.3v devices from potentially external over voltage events (microcontroller driving 5vcircuits).
     
    jjk, Oct 31, 2013
    #17
  18. jjk

    Guest

    On Thu, 31 Oct 2013 11:42:25 -0400, Tom Biasi <>
    wrote:

    >On 10/30/2013 2:04 PM, jjk wrote:
    >
    >> I am now relieved that my sanity on this issue is intact, but still frustrated at not being able to find any functional zener diodes. I received a phone
    >> call from a tech at Jameco Electronics stating they took delivery of another 50 3.3v zener diodes, and they all failed their tests the same way they
    > > failed mine.
    >> They concur there is a problem with these devices.
    >>
    >> Thanks to all who replied to my post.
    >>
    >>

    >I guess Jameco doesn't have any incoming QA inspection.


    Doesn't Jameco still sell floor sweepings? I sure wouldn't trust any
    component bought from them.
     
    , Nov 1, 2013
    #18
  19. jjk

    Tom Biasi Guest

    On 10/31/2013 8:58 PM, wrote:
    > On Thu, 31 Oct 2013 11:42:25 -0400, Tom Biasi <>
    > wrote:
    >
    >> On 10/30/2013 2:04 PM, jjk wrote:
    >>
    >>> I am now relieved that my sanity on this issue is intact, but still frustrated at not being able to find any functional zener diodes. I received a phone
    >>> call from a tech at Jameco Electronics stating they took delivery of another 50 3.3v zener diodes, and they all failed their tests the same way they
    >>> failed mine.
    >>> They concur there is a problem with these devices.
    >>>
    >>> Thanks to all who replied to my post.
    >>>
    >>>

    >> I guess Jameco doesn't have any incoming QA inspection.

    >
    > Doesn't Jameco still sell floor sweepings? I sure wouldn't trust any
    > component bought from them.
    >

    I don't know their practices.
     
    Tom Biasi, Nov 1, 2013
    #19
  20. In article <>,
    jjk <> writes:
    > On Thursday, October 31, 2013 4:42:08 PM UTC-4, Andrew Gabriel wrote:
    >>
    >> This exactly matches the datasheet, which says it needs at least 76mA
    >> in order to act as a zener voltage reference.
    >>
    >> This is a common issue with low voltage zeners - the current they
    >> need to operate is high (compared with higher voltage zeners).
    >>
    >> If you want a low voltage reference at low current (e.g. for battery
    >> operated equipment), an LED can often be used (forward biased) at a
    >> much lower operating current (1mA or less), although not quite as
    >> stable a reference.

    >
    > Thanks for your comments Andrew.
    > I'm wondering why the zener would conduct at all at voltages as low as 1.4v?


    Zener voltage regulation happens in reverse breakdown mode.
    All zeners leak reverse current at voltages below the breakdown voltage.
    With low voltage zeners, this leakage current is very high, up to 76mA
    for this part number. This makes low voltage zeners unsuitable for
    many applications, where you might expect a theoretically perfect
    zener to work.

    > My goal was not to use the zener as a regulator, but to protect 3.3v devices from potentially external over voltage events (microcontroller driving 5v circuits).


    If the 50mA or so leakage at 3V is an unacceptable issue for you,
    you might instead consider a potential divider across the 3V supply,
    with the centerpoint connected to an SCR gate to crowbar the supply.
    Adjust the potential divider ratio to give the right tripping voltage.
    A red led (forward biased) added at the top of the potential divider
    might make it more accurate/sensitive.

    I haven't actually tried this at such a low voltage, but I suspect it
    may work better than a zener.

    --
    Andrew Gabriel
    [email address is not usable -- followup in the newsgroup]
     
    Andrew Gabriel, Nov 1, 2013
    #20
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