An opto-isolator contains a source (emitter) of light, almost always a near infrared light-emitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel, and a photo sensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a Triac. Because LEDs can sense light in addition to emitting it,construction of symmetrical, bidirectional opto-isolators is possible.
OPTO COUPLER (4 Pin)
1. LED ANODE
2. LED CATHODE
3. PHOTO TRANSISTOR COLLECTOR
4. PHOTO TRANSISTOR EMITTER.
optocoupler-4N35-datasheet Click here. photo-interup-datasheet
OPTO-COUPLER TESTING: 6-PIN TYPE (DMM MEANS (DIGITAL MULTIMETER)
Negative black lead to pin-2 (LED CATHODE)
Display reading shows .983v (983 mV)
Connect DMM positive Red test lead to pin-6 (BASE)
Negative black lead to pin-5 = .618V (COLLECTOR)
Negative black lead to pin-4 = .648V (EMITTER)
Display reading shows
positive red lead to pin-5
positive red lead to pin-4
Display reading shows OL
PIN -3 No connection (6 PIN TYPE OPTOCOUPLER)
Verification: If you get reading in forward bias as 0000 or OL or 1, and in reverse bias as 0000 (or) low values the opto coupler can be FAULTY and needs replacement.