To measure CTR of incircuit Optocouplers

Discussion in 'General Electronics Chat' started by nileshkhupase, Oct 31, 2012.

  1. nileshkhupase

    Thread Starter Member

    Mar 22, 2011
    Hello, can anyone please tell me, is there any method to measure current flowing through diode (If) and phototransistor (Ic) of optocouplers (IN-CIRCUIT) without doing any changes or inserting any component in original design.
    I wanted to design a circuit which can measure the current flowing through a diode or phototransistor without disturbing actual circuit.....
  2. timescope


    Dec 14, 2011
    Use Ohms law to calculate the diode current by measuring the voltage drop across the current limiting resistor that is in series with the diode. The photo-transistor often does not have any series resistor and is connected directly to the feedback pin etc. To test in circuit, I use my ancient analog meter on Ohms x10 to bias the LED and my digital meter on diode range connected to the photo-transistor (+ to collector, - to emitter):four probes, two hands.