EN
Three-phase solid state relay (Solid State Relay, abbreviated SSR) is a non-contact switch composed of microelectronic circuits, discrete electronic devices, and power electronic power devices; it is a kind of two terminals as input terminals and the other two terminals. It is a four-terminal device at the output end, and an isolation device is used in the middle to realize the electrical isolation of the input and output. The input end of the solid state relay uses a tiny control signal to directly drive a large current load.
Working principle: When a suitable control signal IN is applied to the input, the P-type SSR is turned on immediately. When IN is removed and the load current is lower than the triac holding current (AC commutation), the SSR is turned off. The Z-type SSR includes a zero-crossing detection circuit. When the input signal IN is applied, the SSR can be turned on only when the load power supply voltage reaches the zero-crossing region, which may cause a maximum delay of half a cycle of the power supply.
The Z-type SSR has the same shutdown conditions as the P-type, but is widely used because the load operating current is approximately sine wave and the interference of high-order harmonics is small. The SSR of Beijing Lingtong Electronics Co., Ltd. is divided into ordinary type (S, using bidirectional thyristor element) and enhanced type (HS, using unidirectional thyristor element) due to different output devices.
When an inductive load is added, before the input signal is cut off at t1, the triac is turned on, and the current lags the power supply voltage by 90O (for pure inductance). At the moment of t1, the input control signal is cancelled, the triac is turned off when it is less than the holding current (t2), and the thyristor will withstand the reverse voltage with a high voltage rise rate dv/dt.
