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low-droput regulator questions

Discussion in 'Electronic Basics' started by spencer, Nov 7, 2004.

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  1. spencer

    spencer Guest

    i am a newbie at electronics and am trying to build this:

    http://www.geocities.com/CapeCanaveral/Launchpad/3632/pc_therm.htm

    it isn't working. i may be installing the LM2936-z5 incorrectly. i am
    working on the assumtion that the middle post is the ground. also, the
    guy at the electronics store said that the lm2936cz-5 was the same as
    the lm2936-5 just made by a different company. are either of these
    correct?

    thanks.
     
  2. The TO92 version (Like a transistor) has input - gnd - output when viewed
    holding the pins facing towards you and the flat on the bottom.
    Download the data sheet from the National site.
     
  3. Reading from left to right that is !!
     
  4. You might have fried the regulator. You can easily test it with a few
    batteries, a resistor, and a multimeter.

    4 AA cells, connected up in series, along with a 1k resistor, hooked up
    as follows:

    LM2936-5
    .-------.
    |in out|
    .-----| |---.
    | | gnd | |
    | '-------' |
    + | | |
    --- | |
    - | o------------ DMM +
    | | | ^
    + | | | |
    --- | | |
    - | \ |
    | | / 1k | 5V
    + | | \ |
    --- | / |
    - | | |
    | | | v
    + | | o------------- DMM -
    --- | |
    - | |
    | | |
    | | |
    '---------o-------'

    Hold the LM2936 case with the markings (flat side) towards you,
    and the pins down. Then the left pin is Vout, the
    middle pin is GND, and the right pin is Vin.

    Use 1.5V AA batteries to test. 4 in series = 6V. The minimum input
    voltage is 5.5 for the LM2936

    created by Andy´s ASCII-Circuit v1.25.250804 www.tech-chat.de

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  5. Ban

    Ban Guest

    The CTS-line will put out voltage before the supply voltage is generated.
    This will blow the temperature sensors. They will then have a huge current
    draw and the regulator cannot supply that and stays at a voltage around 1V.
    The whole design shows your digital abilities, but adaequate skills in
    analog seem to be missing.
     
  6. CTS is an input to the PC. RTS or DTR might come up initially, but the
    inputs are protected using those 4.7k resistors and 5.1V zeners. I'm not
    sure how much protection that really gives, though. A diode from the SCL
    and SDA lines to the 5V rail might help if this is really a problem.
    That would certainly prevent the inputs from getting much higher than Vcc.

    This would probably be a better parallel port project, actually,
    although I think the programming would be harder. Using the parallel
    port, he could dispense with the regulator altogether, since it's all 5V.

    Also, I don't think the OP designed it.


    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  7. Ban

    Ban Guest

    We do not have an RS232 protocoll here, but the designer tries to simulate a
    two wire bus with SCL (system clock) and SDA (bidirectional data) the sensor
    only functions if SDA receives the right address, so the SDA will always
    send from the PC to poll data from the sensors. even if the line cannot go
    above 6V with the 50mA output current of an RS232 driver, this is enough to
    drive the sensors into a latch up when the supply voltage is not yet at +5V,
    generating high supply current and eventually destroying the sensors.
    I do not think this circuit will work as drawn on the website, even if the
    guy claims to have won "design" prices, well maybe from Elektor. :)
    The only reasonable solution would be to use a dedicated RS232 driver IC
    here.
     
  8. spencer

    spencer Guest

    thanks for all the responses. i do/did have the regulator installed
    correctly. at the Vin side i am getting 9V, the Vout side nothing.
    this is a new regulator(it appears the old one was still good, but i
    used a new one to be thorough). is 9V to much?

    thanks again to everyone for their suggestions and help.
     
  9. The max input voltage is 40V. Take a look at the datasheet here:

    http://cache.national.com/ds/LM/LM2936.pdf

    I'm not sure what to tell you. Did you test the regulator in a separate
    battery powered circuit, like I indicated in another branch of this thread?

    Note that if Ban is correct, there will be a short through the
    temperature probe, and it'll pull the output voltage down. Thus, if you
    are testing the regulator in circuit, that may be your problem.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  10. spencer

    spencer Guest

    sorry it has taken so long to reply, been really busy with work
    stuffs.

    i took a new regulator and tested it with a new 9V battery. to do this
    i put the regulator on a breadboard, hooked the batterie's - side to
    the ground on the regulator. the the + side to the Vin. i set my volt
    meter to "20". at Vin it reads 9.66V at Vout it reads 7.29V. something
    interesting, according to the pdf datasheet below using the flat part
    of th to-92 the left pin is Vin. if i hook it up like that the voltage
    reads the same at both sides(9.33 i think).

    i think that i must be missing something.
     
  11. No, you need to look at the datasheet again. That view is from the
    bottom. Thus, with the flat part facing you, and the pins down, the pins are

    1 2 3
    VOUT GND VIN

    If you put a reverse voltage on most regulators, they will be destroyed
    in short order. However, this one has 'reverse battery protection'. I am
    not sure if that means you can reverse VOUT and VIN, or if it means you
    can reverse VIN and GND. It actually looks like it might withstand this
    from the schematic in the datasheet, so who knows?

    You may also need a load on the regulator. Use a 1k from VOUT to ground.

    Also, the datasheet calls for capacitors on input and output. However,
    since you are driven by a battery, that doesn't seem that important. If
    you have a 0.1uF cap and a 10uF cap, put the 0.1uF cap on the input, and
    the 10uF cap on the output.

    Other than that, I don't have any suggestions.

    Good luck.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  12. spencer

    spencer Guest



    actually nevermind. i got it to work. using batteries instead of
    trying to power it off the serial port. thanks for the help.
     
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