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test a phototransistor with esr meter

MikeMl

Well-Known Member
Most Helpful Member
#6
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.
 
Thread starter #7
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:

Nigel Goodwin

Super Moderator
Most Helpful Member
#8
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 .
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.
 
Thread starter #9
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
 

schmitt trigger

Well-Known Member
#10
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.
 

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