The composition of solid state relay into, equivalent, compatible, convenient, different

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Solid state relay is composed of three parts: input circuit, isolation ( coupling ) and output circuit.
In 1, the input circuit
According to the input voltage of different classes, the input circuit can be divided into DC input circuit, an AC input circuit and a DC input circuit three. Some input control circuit also is compatible with TTL/CMOS, positive and negative logic control and the equivalent function, can be convenient and TTL, MOS logic circuit connection. For the control of fixed voltage control signal, using a resistive input circuit. Control current guaranteed at greater than 5mA. For a large range of control signals ( such as 3~32V ) is a constant current circuit, the whole voltage range current at greater than 5mA reliable work.
2, isolation ( coupling )
Solid state relay input and output circuit and method of coupling with a photoelectric coupling and the transformer coupling two: photoelectric coupling typically use photoelectric diode, a photoelectric triode, diode, two-way silicon controlled, photovoltaic cells, realize the control side and the load side isolation control; high-frequency transformer coupling is the use of the input control signal is generated. Self-excitation high-frequency signal is coupled to the secondary, the detection rectification, the logic circuit to form driving signals.
In 3, the output circuit
SSR power switch is directly connected with the power source and the load, the load power on-off switch. The main use of large power transistor ( switching tube -Transistor ), a unidirectional controlled silicon ( Thyristor or SCR ), a bidirectional controllable silicon ( Triac ), a power field effect transistor ( MOSFET ), insulated gate bipolar transistor ( IGBT ). Solid state relay output circuit can also be divided into the DC output circuit, the AC output circuit and the DC output circuit form. According to the type of load, can be divided into DC solid state relay and an AC solid state relay. DC output can be used when a bipolar device or power field effect tube, AC output usually use two controllable silicon or a bidirectional controllable silicon. While the AC solid state relay can be divided into single phase AC solid state relay and three phase AC solid state relay. AC solid state relay, according to the turn-on and turn-off time, can be divided into random type AC solid state relay and zero type AC solid state relay.
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