Thyristor zero-crossing detection circuit diagram

The moment when the thyristor is put into the capacitor , that is, the moment when the thyristor is turned on, must be the moment when the amplitude and phase of the power supply voltage and the residual voltage of the capacitor are the same. Because according to the characteristics of the capacitor, when the voltage applied to the capacitor changes stepwise, an inrush current will occur, which will damage the thyristor and bring adverse effects such as high-frequency oscillation to the power system. Therefore, a thyristor zero-crossing detection circuit is designed to solve the problem of residual voltage measurement. The thyristor zero-crossing detection circuit is shown in Figure 3.

When the power supply voltage is equal to the residual voltage of the capacitor, the voltage on the thyristor is zero, and the photocoupler will output a falling edge negative pulse to the INT0 and INT1 pins of the microcontroller. If the controller input command exists at this time, this pulse will pass through a In a series of steps, a pulse train is generated to trigger the thyristor to ensure the conduction of the thyristor and the capacitor is put in smoothly; when the power supply voltage is not equal to the residual voltage of the capacitor , the voltage on the thyristor is not zero, the optocoupler is turned on, and is connected to the INT0 and INT0 of the microcontroller. INT1 is at high level. If this situation is set in the software, no trigger pulse will be generated, and the thyristor will be in the off state.