How To Test Opto-coupler (Find Bad Opto-coupler)

Opto-coupler: 
                     opto-coupler, photo-coupler, or optical-isolator, is a component that transfers electrical signals between two isolated circuits by using light. Opto-isolators prevent high voltages from affecting the system receiving the signal. Optocouplers are available in four general types, each one having an infra-red LED source but with different photo-sensitive devices. The four optocouplers are called the: Photo-transistor, Photo-darlington, Photo-SCR and Photo-triac as shown below.

Method #1:

• Part's Required: Multimeter or ohm meter, opto-coupler,100 Ohm resistor,push button,battery or power supply.
• Turn ON multimeter and select Resistance mode.
• Now, Connect the multimeter ( X1K Ohm or  X10K Ohm ) between emitter and collector like this: red probe to collector and black probe to emitter. 
• Now, connect a resistor of a few hundred ohms (100 ohms) in series with the LED anode, after this turn on the power supply, press the push button and start increasing the voltage from 0 to 2…5 volts, and you should be able to see on the ohmmeter how the output resistance decreases as the input voltage increases and viceversa.
• the Optocoupler IC is Good. else if the Optocoupler IC is Bad.

Method #2:

• Part's Required: Multimeter or ohm meter, opto-coupler,100 Ohm resistor,push button,battery or power supply.
• Turn ON multimeter and select DC Voltage mode.
• Now, connect a resistor of a few hundred ohms (100 ohms),Push button in series with the LED anode,after give +5V DC power supply to this circuit. 
• if the push button is press: display the voltage reading is near 0V or 0.2V DC. else the push button is unpress: display the voltage reading is near 5V or 4.9V DC. the Optocoupler IC is Good. else if the Optocoupler IC is Bad.

Method #3:

• Part's Required: Multimeter or ohm meter, opto-coupler,100 Ohm resistor,push button,battery or power supply.
• Turn ON multimeter and select DC Voltage mode.
• Now, connect a resistor of a few hundred ohms (100 ohms),Push button in series with the LED anode,after give +5V DC power supply to this circuit. 
• if the push button is press: LED will ON. else the push button is unpress: LED will OFF. the Optocoupler IC is Good. else if the Optocoupler IC is Bad.

Few Applications:

• Solenoid/valve controls
• Lamp ballasts
• Interfacing microprocessors to 115/240 Vac peripherals
• Motor controls
• Incandescent lamp dimmers