Transistor undervoltage reset circuit

The working principle of the undervoltage reset circuit (as shown in the figure) w When the power is turned on, the +5V voltage starts to rise from "0V". Before rising to 3.6V, the Zener diode DH03 is in the cut-off state, and QH01 (PNP tube) is also in the Cut-off state, no reset voltage output.

When the +5V power supply voltage is higher than 3.6V, the Zener diode DH03 reversely breaks down and "clamps" the voltage at both ends at 3.6V.

When the +5V power supply voltage is higher than 4.3V, QH01 begins to conduct, and the reset voltage begins to form. When the +5V power supply voltage approaches +5V, QH01 has saturated conduction, and the reset voltage reaches a stable state.