Zero-crossing trigger circuit design based on thyristor

Probe current voltage pin 290*3600 needle head diameter is 3.5mm can be too large

Circuit principle : The zero-crossing sync pulse is a pulse of 50Hz AC voltage zero-crossing moment, which can make the thyristor trigger the conduction when the AC voltage sine wave crosses zero. The zero-crossing sync pulse is generated by the zero-crossing trigger circuit. A more detailed circuit diagram is shown. In the figure, the voltage comparator LM311 is used to convert a 50 Hz sinusoidal alternating voltage into a square wave. The positive and negative edges of the square wave act as the input trigger signals of the two monostable flip-flops respectively. The two narrow pulses of the monostable flip-flop output are mixed by the diode or the gate to obtain the corresponding 220V AC power. Zero sync pulse. This pulse is applied to the temperature control circuit as a trigger sync pulse of the thyristor on the one hand, and to the T0 and T1 terminals of the 8031 ​​as a count pulse on the other hand.