How to identify the pinout of a white label LM337?

Discussion in 'General Electronics Chat' started by amundsen, Aug 30, 2015.

  1. amundsen

    Thread Starter New Member

    Aug 27, 2015
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    Hello,

    I have a LM337 regulator in a TO-220 package which appears to lack any identification of the component's manufacturer. The only writings are "LM337" and "A4". Therefore I can't refer to any specific datasheet.

    Any idea how to identify the pins without frying the component by trial and error?

    Thank you in advance.
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    The textbook transistor model is a pair of back-to-back diodes - so you should be able to identify the base pin easy enough.

    You can distinguish between emitter and collector because the B/E junction acts like a zener at somewhere around 8V ish.

    You can get ultra efficient LEDs that give a useable indication at only 2mA, use a 12V A23 keyfob battery and the highest value resistor you can get away with to limit the current.

    The B/E junction will conduct one way, and pass enough leakage current for a dim glow in the LED when the other way.
     
  3. CoolBeer

    Active Member

    Mar 29, 2010
    40
    6
    But it's not a transistor now is it, it's a voltage regulator...


    I would just go by any reputable manufacturers datasheet(say TI), I'd be very surprised if it does not turn out that all lm337s have the same pinout. (ADJ-VIN-VOUT btw).


    Hope this helps.
    -
    CoolBear
     
    Roderick Young and amundsen like this.
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    Speed reading - I read it as BC337.

    It is an industry standard pin layout for 3 terminal regulators - but not in logical order for the negative ones.
     
  5. amundsen

    Thread Starter New Member

    Aug 27, 2015
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    Indeed, it's the same pinout from TI, Fairchild, OnSemi and ST. However I have already encountered components (maybe not as common as this one) with different pinouts from manufacturer to manufacturer, so I preferred to ask first.

    Thank you.
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    As a public service, I'd like to point out that breaking down the BE junction tends to kill the high frequency beta; I've read that low frequency beta is unaffected, but haven't confirmed this myself.

    The breakdown voltage should be closer to 5V.
     
  7. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    google it
     
  8. crutschow

    Expert

    Mar 14, 2008
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    3,238
    Wire it according to any manufacturers LM337 pinout with the ADJ pin connected to ground and no output load.
    Slowly increase the input voltage while monitoring the input current and output voltage.
    The output voltage should start to rise when the input exceeds -2V or so and reach a maximum of -1.3V if it is connected properly.
    The input current should be essentially zero.
    If either of these don't happen then it's connected wrong.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    It varies with transistor type, from about 5V but can be as high as 8V.

    This was meant to illustrate the reason for using a 12V A23 keyfob battery, as a 9V PP3 might not have enough oomph to also glow the LED if the B/E breakdown only left 1V to spare.
     
  10. amundsen

    Thread Starter New Member

    Aug 27, 2015
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    Thanks crutschow !

    By the way this thread is a bit strange, with two subjects in one. :)
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Yes, sometimes a misunderstood question (such as here, thinking the LM337 was a transistor) can lead to a side discussion that achieves a life of it's own, even after it's recognized that the side discussion is unrelated to the op's question.
    So you have to read the replies carefully to see which apply to your question and which don't. :rolleyes:
     
    Last edited: Aug 31, 2015
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