Thyristor zero-crossing switch temperature controller circuit

Circuit working principle: by IC. ,VT,T. Form a zero-crossing trigger circuit. After bridge
rectification, the pulsating DC voltage is sent to the IC. The inverting input pin 1 and the output pin 2 will
generate a 0.5-1 ms pulse voltage at each zero-crossing moment and send it to the base of VT.
During this period VT is saturated and the remaining time is cut off. At T: the secondary will get a pulse voltage
(pin 4) to trigger the thyristor. Because this signal is synchronized with the power supply,
zero-crossing triggering is achieved. IC2, R6, R7, RP,, R. etc. form a temperature control circuit. When the external
temperature is lower than the set temperature, the "+" terminal voltage of IC2 is higher than the "-" terminal, and the output
is high level, VD, reverse bias cut-off, which has no effect on the trigger circuit. When the temperature rises and
the RT resistance decreases to the point where the voltage at the "+" terminal is lower than the "-" terminal, pin 3 of IC2
outputs a low level, which is equivalent to moment t when VD7 is turned on. At this time, when the power supply crosses zero Finally, due to
the #: pulse being short-circuited by VD, the thyristor is turned off. As the temperature drops, the resistance
value of RT rises again, and the voltage of the "+" terminal at time L is higher than that of the "-" terminal, and the output is high level,
but is blocked by VD, reverse bias, and only when Ic, output pulse at time T , the thyristor is triggered
to conduct again, thereby realizing zero- crossing switching . In the figure, IC, LED, etc. form an indication circuit
.