Triac circuit diagram with flip-flop TcA 780

as the picture shows. The integrated flip-flop in the circuit in Figure a can output a double half-cycle +50mA forward current to control a bidirectional thyristor with a rated voltage of 700V .

Figure b shows a circuit that outputs reverse control current. The +15V power supply charges the 0.22uF capacitor through the 10k ohm resistor. The charging polarity is as shown in the figure, and the transistor BC238 is cut off. When the pulse generated by the integrated trigger is added to the base of the transistor through the two diodes, the transistor is turned on, and the upper end of the capacitor is grounded through the transistor, thus generating a reverse trigger current on the gate of the thyristor, causing it to turn on.