Important Parameters of Optocouplers

1. Isolation voltage
The maximum voltage that can be withstood between the input and output terminals without any piezoelectric breakdown is called the isolation voltage V.iso. They have specific values up to 7500 AC volts.

2. Current transfer ratio or click rate
The ratio between the output (phototransistor) current and the input (LED) current is called the current transfer ratio and is expressed as a percentage. A phototransistor may have an output CTR value between 50% and 150%. Whereas in the case of Photo Darling Ton output, its specific value is between 50% and 500%.

3. Response time
It is divided into rise time (tr) and charge time (tl). The tr and tl of the output stage of the phototransistor are close to about 2-5 microseconds.

4. Transmission gain
This parameter is associated with opto-isolated AC linear couplers. The ratio between output voltage and input current is called transfer gain. Its defined value is 200mV/mA.