Latching power switch uses momentary-action pushbutton

Anthony Smith @ edn.com published a push button latching circuit able to control a load with a single push of a button.

The circuit in Figure 1 shows how you can use a simple, momentary-action, SPNO (single-pole, normally open) pushbutton switch to latch power to a load. Requiring just a handful of common, garden-variety components, the circuit works over a wide voltage range and is ideal for single-cell applications, because it can operate at voltages as low as 1V or less. Transistors Q₂ and Q₃ form an SCR-like structure that functions as a simple latch, Q₄ switches power to the load, and S₁ is the momentary pushbutton switch.

Latching power switch uses momentary-action pushbutton – [Link]

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