Common knowledge that optocoupler relays need to know in daily use

1. There are many varieties and types of optocoupler relays, and in practical applications, different types of optocoupler relays should be selected according to different circuits. For example, an optocoupler relay with two "back-to-back" light-emitting diodes in the input section is suitable for applications involving AC input; The optocoupler relay with Darlington output structure is suitable for applications with high output current; The output is an optocoupler relay composed of light triggered bidirectional thyristors, suitable for driving AC loads.
2. The packaging form, internal structure, and circuit function of optocoupler relays are completely different things. Optocoupler relays with the same appearance may have completely different functions; Circuits with the same functionality can also be packaged differently. So when selecting or replacing optocoupler relays, it can only be based on their model. In addition, when optocoupler relays are directly used for isolating and transmitting analog signals, their output nonlinearity must be considered. When used for isolating and transmitting digital data, its response speed should be considered. If there are power requirements for the output, power interface design issues also need to be considered.
3. In terms of output characteristics, there are two types of optocoupler relays: nonlinear (digital) optocoupler relays and linear (analog) optocoupler relays. The current transmission characteristic curve of nonlinear optocoupler relays is nonlinear, and these products are suitable for transmitting switch signals but not for transmitting analog signals. The current transmission characteristic curve of linear optocoupler relay is close to a straight line, and it performs well in small signals, and can be isolated and controlled with linear characteristics. The optocoupler relay commonly used in switch mode power supplies for televisions, monitors, etc. is a linear product. If it is replaced with a nonlinear product, it may cause the oscillation waveform to deteriorate, and in severe cases, parasitic oscillation may occur, which can interfere with the image and reduce the load capacity of the power supply. Therefore, when repairing the switch power supply of household appliances, if the optocoupler relay is found to be damaged, be sure to replace it with a linear optocoupler relay.
4. The establishment of the "isolation" function of optocoupler relays requires certain external conditions to be met: firstly, independent power sources must be used for the input and output parts of the optocoupler relay. If both ends share the same power source, the isolation function of the optocoupler relay will be meaningless. Secondly, when using optocoupler relays to isolate input and output channels, all signals (including digital signals, control signals, and status signals) must be isolated so that there is no electrical connection between the isolated sides. Otherwise, this isolation is meaningles