This circuit works similar to a SCR. When the trigger input is high, Both transistors Q2(PNP transistors) and Q1(PNP transistor) will work. Therefore, a current flow to the base pin of Q2, it has voltage 0.7 volts at resistor R1.
When cutting the activation voltage, the transistors can continue to perform, because the base current. The reset circuit will do this by cutting the power supply circuit. Which this circuit we press the switch Reset button only.
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