Double button switch circuit diagram explanation

This is a two-button electronic switch, let's see how it works.

When the power is turned on, both transistors are in the cut-off state, and the circuit is blocked, which is equivalent to a closed switch.

When the ON button is pressed, the NPN transistor obtains bias current and turns on. After the voltage is loaded to the load, a voltage is generated at both ends of RL. This voltage causes the PNP transistor to turn on and provide bias current to the NPN transistor, forming an interlock. When the ON button is released, the circuit remains on, allowing the load to continue working.

Press the OFF button, the PNP transistor is turned off, and the NPN transistor is also turned off due to the loss of bias current, and the circuit is closed.

It can be seen that this electronic switch will reduce the operating voltage of the load by about 1V, and RL needs to be set according to the load current. The maximum current that the electronic switch can withstand depends on the resistor RL and the NPN transistor.