Push Button ON-OFF Soft Latch Circuits


Posted on Feb 5, 2014

This page provides soft power switch circuits for toggling electronic devices ON and OFF with a momentary button press that controls a latching high-side MOSFET power switch. Several micropower latching switch circuits are provided. Owing to their low current in the OFF state, they`re well suited to battery operated portable instruments. Feel free


Push Button ON-OFF Soft Latch Circuits
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to use these circuits as is, or modify them for your needs, wherever you might need a power bus switch circuit. The soft power switch circuit designs shown on this page provide both functions. You may also be interested in ON/OFF switches that limit capacitor in-rush currents, or switches to specifically turn ON/OFF microcontroller products. Using a single tactile switch button to alternately toggle a circuit ON and OFF requires a circuit containing a bistable logic latch. Such a latch can be implemented using a D flop flop, or by using positive feedback around any two inverting amplifiers or logic gates. For example, a basic latching ON-OFF switch can be implemented using a dual NAND gate, using this circuit: A brief button press toggles the output state of this NAND gate latch. Any CMOS NAND gate can be used, including Schmitt trigger gates. In fact, any inverting devices can be used with minor changes to the circuit: a hex inverter, open collector inverters, NAND or NOR gates, transistors, FETs or MOSFETs. When power is first applied, the capacitor at the input of the first gate guarantees that the latch output, Vout, is initially latched low. Thereafter, button presses toggle the output high and low. This circuit uses only a single active device, the surface mount dual MOSFET, yet toggles ON and OFF currents of up to 4 Amp. The load may be just about any electrical device, from high power LED lights to the power supply...




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