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test a phototransistor with esr meter

Discussion in 'General Electronics Chat' started by KevinW, Dec 31, 2017.

  1. KevinW

    KevinW Member

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    Would an esr meter identify a photo transistor with or without the presence of light?
     
  2. kubeek

    kubeek Well-Known Member

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    Most likely not.
     
  3. KevinW

    KevinW Member

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    You're right, I just tested a new one I had and it won't identify it.
    Thanks.
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Not a chance, esr meters test for low impedances, using 100KHz (usually) and low signal levels, far too low to trigger a silicon junction (and for that very reason).
     
  6. KevinW

    KevinW Member

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    Thanks for the explanation Nigel.
     
  7. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Try an Ohmeter that has a "diode" test mode. It will put enough DC bias on the device under test so you should be able to see the change in "resistance" due to illumination falling on the junction.
     
  8. KevinW

    KevinW Member

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    Thanks Mike.
    There is a voltage drop in diode mode with illumination.
    Opposite the transistor, I'm not measuring any voltage drop on the diode using my multi meter but the esr meter is identifying the diode and measuring Uf=1.14v and C=18pF .

    Upon rechecking the diode with the multi meter in diode test, I'm measuring a 2 volt drop which seems excessive.
     
    Last edited: Jan 1, 2018
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    An ESR meter wouldn't give a value of 1.14V, or indeed a capacitance of 18pF, so presumably you're NOT using an ESR meter, but a component tester? - an entirely different beast.

    A component tester should test a photo-transistor just as a normal transistor, and if you run it multiple times, under light and dark, you should see a difference.
     
  10. KevinW

    KevinW Member

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    This is what they call it ...
    GM328 Transistor Tester Diode LCR ESR meter PWM Square wave Generator

    It identifies the diode with a diode symbol on the display and when the diode is reversed the symbol also appears reversed.
    diode test.JPG
     
  11. schmitt trigger

    schmitt trigger Active Member

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    Build a little circuit in a proto board:

    -. A 4.7k resistor, with one end tied to +5V, the other end tied to the phototransistor's collector.
    -. the phototransistor's emitter tied to the +5V return.
    -. You may try other resistor values later.

    Measure with a DMM the collector-emitter voltage, with different light levels, including as much darkness as you can achieve.
     
  12. KevinW

    KevinW Member

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    Getting about 2vdc drop in the presence of light, appears as if the transistor is working but the diode is dead so I've ordered a new device.
    Thanks for the help.
     

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