There are two types of optical couplers: one is a nonlinear optical coupler and the other is a linear optocoupler.
1. Linear optocouplers are commonly used in switching power supplies. The main difference from ordinary optical couplers is that their current transfer ratio (CTR) is not the same. This is a very important parameter. CTR is an important parameter of optical couplers.
It is usually expressed by the DC current transfer ratio. When the output voltage remains constant, it is equal to the percentage of the DC output current IC to the DC input current IF, that is, ΔCTR=ΔIC/ΔIF.
For linear optocoupler, it is suitable for transmitting analog voltage or current signals, so that the relationship between output and input can be linear. The optical couplers commonly used in switching power supplies are linear optocouplers.
2. The current transfer characteristic curve of the nonlinear optical coupler is nonlinear. This type of optical coupler is suitable for the transmission of switching signals, but not suitable for the transmission of analog quantities. The commonly used 4N series optical couplers are nonlinear optical couplers.
The current transfer characteristic curve of the linear optocoupler is close to a straight line, and the performance is better when the signal is small, and the isolation control can be performed with linear characteristics.