Solid state relay circuit one a

Solid state (body) relay (SSR for short) is a contactless switch assembled from solid semiconductor components.
    Solid-state relays have the characteristics of small control power, high reliability, strong anti-interference ability, fast action (response time of tens of microseconds to
10ms), long life (l012~l013 times), high withstand voltage, and large surge current resistance [(6 ~10)j. ] and a wide applicable voltage range
(any selection within 30-220V), it can be widely used in digital program-controlled devices, computer terminal interface circuits and other
occasions.
    However, solid-state relays also have shortcomings, such as large leakage current, large contact voltage, single contact,
poor temperature resistance and overload capability, etc.
    The circuit is shown in Figure 6-5. Figure 6-5 (b) and Figure 6-5 (c) use AC power supply. Their structures are basically the same, but
the component parameters are different; Figure 6-5 (a) shows a solid relay using DC power supply.
    As shown in Figure 6-5 (b), the circuit consists of photocoupler B, trigger circuit (
composed of transistor VT, thyristor vl, and diodes VD2~VDs), switching circuit (bidirectional thyristor Vz), absorption circuit (resistance R, capacitor C) and The zero-crossing control
circuit consists of a four-terminal device.