The circuit of optocouplers is very common in the circuit. The role of optocouplers in the circuit is to isolate and convert photoelectricity. The types of optocouplers include linear optocouplers and nonlinear optocouplers. Although they are all optocouplers, what is the difference between these two types of optocouplers? How to distinguish them? This article will introduce the difference between linear optocouplers and nonlinear optocouplers.

There are two types of optocouplers: one is nonlinear optocouplers and the other is linear optocouplers.
The current transmission characteristic curve of nonlinear optocouplers is nonlinear. This type of optocoupler is suitable for the transmission of switching signals, but not for the transmission of analog quantities. For example, the 4N series optocoupler belongs to nonlinear optocouplers.

The current transmission characteristic curve of linear optocouplers is close to a straight line, and the performance is better when the signal is small, and it can be isolated and controlled with linear characteristics. The 817 series of optocouplers commonly used in switching power supplies belong to linear optocouplers.

The optocouplers commonly used in switching power supplies are linear optocouplers. If nonlinear optocouplers are used, the oscillation waveform may be deteriorated. In severe cases, parasitic oscillation may occur, causing the oscillation frequency of several kilohertz to be modulated by low-frequency oscillations of tens to hundreds of kilohertz in sequence. The consequence is that color TVs, color displays, VCDs, DCDs, etc. will cause interference on the image screen. At the same time, the load capacity of the power supply decreases.

If the optocoupler is damaged during the maintenance of switching power supplies such as color TVs and monitors, it must be replaced with a linear optocoupler. Commonly used 4-pin linear optocouplers include PC817A-C. PC111 TLP521 and other commonly used six-pin linear optocouplers include: LP632 TLP532 PC614 PC714 PS2031, etc.

Nonlinear optocouplers cannot be used in switching power supply feedback circuits.