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How to explain that the measurement Vf ( P to N ) is 3.3V now

B

Boki

Jan 1, 1970
0
Hi All,

There is a PN diode, P connects 3.3V, N connects to ground.
We knew that Vf is 0.7V.

How to explain that the measurement Vf ( P to N ) is 3.3V now but not
0.7V ...

Best regards,
Boki.
 
M

martin griffith

Jan 1, 1970
0
Hi All,

There is a PN diode, P connects 3.3V, N connects to ground.
We knew that Vf is 0.7V.

How to explain that the measurement Vf ( P to N ) is 3.3V now but not
0.7V ...

Best regards,
Boki.
do you have a resistor in series with the diode, If not you release
the magic smoke from the PN junction


martin
 
T

Tim Shoppa

Jan 1, 1970
0
Boki said:
Hi All,

There is a PN diode, P connects 3.3V, N connects to ground.
We knew that Vf is 0.7V.

How to explain that the measurement Vf ( P to N ) is 3.3V now but not
0.7V ...

By definition, if you hook the anode to a stiff enough voltage source,
that's what happens. Depending on the details of the diode, you
probably have a number of amps going through it and it's getting pretty
warm.

Put more amps through and it will become a "Noise Emitting Diode" (NED)
in the lexicon. As in "hook to a stiff enough voltage source and it
emits a loud noise, once." And not conduct at all anymore.

Everybody else here has blown up diodes, popped the top off of
expensive chips with lots of magic smoke coming out, filtered AC with
electrolytics (making confetti and a gooey residue) etc.

Tim.
 
D

Deefoo

Jan 1, 1970
0
Tim Shoppa said:
By definition, if you hook the anode to a stiff enough voltage source,
that's what happens. Depending on the details of the diode, you
probably have a number of amps going through it and it's getting pretty
warm.

Put more amps through and it will become a "Noise Emitting Diode" (NED)
in the lexicon. As in "hook to a stiff enough voltage source and it
emits a loud noise, once." And not conduct at all anymore.

Everybody else here has blown up diodes, popped the top off of
expensive chips with lots of magic smoke coming out, filtered AC with
electrolytics (making confetti and a gooey residue) etc.

Tim.

Just for the heck of it I just connected a 1N4148 directly to a 3V3 bench
supply. The current was limited to about 2.6A and the diode started glowing
and became a short, not open. It was funny to see how the reddish inside of
the diode became black and then turned red again when the power was switched
off. Part of it was gone. The text on the diode disappeared completely.

--DF
 
B

Boki

Jan 1, 1970
0
martin said:
do you have a resistor in series with the diode, If not you release
the magic smoke from the PN junction


martin

How about use transistor, and put a resistor on collector ( NPN )

The Vbe now is 3.3V.

emitter to ground directly.

Boki.
 
T

Tim Shoppa

Jan 1, 1970
0
Boki said:
How about use transistor, and put a resistor on collector ( NPN )

The Vbe now is 3.3V.

emitter to ground directly.

Boki -

If you are reverse engineering a device (and I'm guessing you are),
then with 99% certainty if the device is still functioning then you've
got one of those SMT transistors with built-in base resistor. Typically
for a NPN switch the base resistor is in the few k to few hundred k ohm
range, depending on what sort of voltages get are being put in and what
sort of current is being switched.

With 3.3V going in and say a 50mA current being switched, you'd
probably end up with a base resistor in the low 1000's of ohms for a
base current in the 1mA region.

I know you like to write cryptic questions, but from your questions
there's no secret that you are spending a good chunk of your time
reverse engineering stuff, so couching all this in your gobbledygook
really isn't helping you.

Tim.
 
D

Deefoo

Jan 1, 1970
0
Boki said:
How about use transistor, and put a resistor on collector ( NPN )

The Vbe now is 3.3V.

emitter to ground directly.

Boki.

How about buying an electronics engineering text book?

--DF
 
B

Boki

Jan 1, 1970
0
Tim said:
Boki -

If you are reverse engineering a device (and I'm guessing you are),
then with 99% certainty if the device is still functioning then you've
got one of those SMT transistors with built-in base resistor. Typically
for a NPN switch the base resistor is in the few k to few hundred k ohm
range, depending on what sort of voltages get are being put in and what
sort of current is being switched.

With 3.3V going in and say a 50mA current being switched, you'd
probably end up with a base resistor in the low 1000's of ohms for a
base current in the 1mA region.

I know you like to write cryptic questions, but from your questions
there's no secret that you are spending a good chunk of your time
reverse engineering stuff, so couching all this in your gobbledygook
really isn't helping you.

Tim.

I think it is a good chance to know more here, but not limited to
reverse engineering : )
 
B

Boki

Jan 1, 1970
0
Deefoo said:
Just for the heck of it I just connected a 1N4148 directly to a 3V3 bench
supply. The current was limited to about 2.6A and the diode started glowing
and became a short, not open. It was funny to see how the reddish inside of
the diode became black and then turned red again when the power was switched
off. Part of it was gone. The text on the diode disappeared completely.

--DF

Haha..
 
J

Jim Thompson

Jan 1, 1970
0
Hi All,

There is a PN diode, P connects 3.3V, N connects to ground.
We knew that Vf is 0.7V.

How to explain that the measurement Vf ( P to N ) is 3.3V now but not
0.7V ...

Best regards,
Boki.

Boki, Are you really that ignorant?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Old Latin teachers never die...they just decline
 
B

Boki

Jan 1, 1970
0
Jim said:
Boki, Are you really that ignorant?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

Old Latin teachers never die...they just decline

Please take easy, I can still get some : )
 
K

Ken Taylor

Jan 1, 1970
0
Boki said:
Please take easy, I can still get some : )
Be grateful for the air compressor and puncture repair kit.

Ken
 
J

joseph2k

Jan 1, 1970
0
Tim said:
By definition, if you hook the anode to a stiff enough voltage source,
that's what happens. Depending on the details of the diode, you
probably have a number of amps going through it and it's getting pretty
warm.

Put more amps through and it will become a "Noise Emitting Diode" (NED)
in the lexicon. As in "hook to a stiff enough voltage source and it
emits a loud noise, once." And not conduct at all anymore.

Everybody else here has blown up diodes, popped the top off of
expensive chips with lots of magic smoke coming out, filtered AC with
electrolytics (making confetti and a gooey residue) etc.

Tim.

Let me see, i have blown up several transistors (including a to-3), many
resistors and capacitors in various ways. Never connected an electrolytic
to AC, connected a few to way above rated voltage (15V part to over 60V),
(toxic, had i known at the time) confetti all over the garage. Expensive
IC's however were lost to ESD (previous adventures had taught me to more
careful / respectful of expensive parts; i was just a tween).
 
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