AC solid state relay circuit with good reliability

AC solid state relay (AC·SSR), also known as AC non-contact switch, can achieve the purpose of weak control and strong isolation in logic control appliances such as computer control. This article recommends to readers a simple, easy-to-use, stable, and easy-to-make AC solid-state relay. Because it does not require high component specifications, it reduces costs. The following figure is the circuit diagram of this AC solid state relay, in which DIAC is a bidirectional diode to ensure the reliable conduction of the triac SCR; after the triac is turned on, the DIAC is used to protect the phototransistor from breakdown; and The power of the trigger branch is reduced by utilizing the conduction voltage stabilizing characteristics of DIAC and the phase-shifting effect of capacitor C1. Due to the use of DIAC, many thyristors that are difficult to trigger in other circuits and are screened out can be reused and work stably. R* in the figure is generally selected from 100 to 150Ω. The main consideration is to make the optocoupler OPC work reliably; D1 is designed to protect the optocoupler. The AC RC branch formed by R1 and C1 is rectified by D2~D5 as the excitation source of the trigger loop. R2 and C2 are RC absorption networks to prevent false triggering under inductive loads; C3 is used to suppress high-frequency interference. For the bidirectional diode, choose DIAC produced by Beijing Chunshu Rectifier Factory. The turning voltage VBO ≥ 20V and the complex voltage ≥ 5V are enough (the peak output current generally meets the triggering requirements); for the photoelectric coupling, choose any GD310~315 from Beijing Optoelectronic Device Factory. Any type can be used; there are no strict requirements for triacs, as long as they are good pipes, they can generally be used.