Optocoupler is a commonly used isolation device. Since the front and rear ends use light to "communicate", the front and rear ends are not affected at all, so the isolation effect is very good. The specific characteristics of optocouplers move to Baidu.
The representation of the optocoupler in the circuit schematic diagram is generally as follows: the
optocoupler device has a very special parameter called Current transfer ratio referred to as CTR, which is the current conversion ratio, that is, the current IF of the front LED and the current IC of the rear collector. Ratio, the following figure is an example:
Current transfer ratio CTR = IC ÷ IF, according to the value of CTR, the optocoupler is divided into many gears, as shown in the figure below:
For example, I bought a PC817C optocoupler, check the data sheet:
It can be seen that the CTR of the C-position optocoupler in the PC817 model is 200% to 400%, which means that the current IC / IF is between 200% and 400%. In this way, when the current of the light-emitting diode at the output end is the same, the higher the CTR of the optocoupler, the higher the maximum current at the output end, which is equivalent to the same current amplification factor of the triode. Therefore, the higher the sensitivity of the optocoupler is, the higher the sensitivity of the optocoupler is. As long as a little light at the input end can have a relatively large current at the output end, it does not mean that the higher the better, it depends on the application.