Zero trigger integrated circuit temperature control circuit 5

Since the capacity of the bidirectional thyristor is greater than 50A, pulse broadening and power amplification
circuits are used. The entire circuit consists of a regulated power supply, a zero-trigger circuit, a pulse broadening circuit, and a power amplifier circuit. The temperature measuring element has a negative
temperature coefficient thermistor only. . Since the load is the inductive salt bath furnace transformer Ti, a zero-current trigger circuit is used.
    The pulse broadening and power amplification circuit is composed of transistors VTz~VT4 and corresponding resistor-capacitor components.
    In the figure, diode VD4 can provide a charging circuit for capacitor c5} The tube voltage drop of VD6 can ensure that VT4 is reliably turned off when VTa is turned on
, and VT4 is turned on when VTa is turned off; VD7 is used to prevent interference from the pulse transformer TM.
    By changing the values ​​of capacitors c5, C6 and resistor Rl1, the pulse width can be adjusted. If the pulse width is Ims (approximately 18 electrical
degrees), a 200A bidirectional thyristor can be triggered reliably.