Momentary push button soft latching toggle on off switch circuit

momentary push button soft latching toggle on off switch circuit


Momentary push button soft latching toggle on off switch circuit

This is a momentary push button switch circuit for toggling electronic devices ON and OFF. When you push once this circuit set to ON and push again circuit set to OFF.

Another advantage of that circuit is a some loads need to be switched on from one location and switched off from another. Any number of momentary push buttons can be connected in parallel.

The circuit is off when we connect power to the circuit. That one is very good feature because many circuits are on when we connect to power.

There is no current flow when circuit is off.  Actually circuit flow ≈ 10µA ≈ 0A. So this is very good for battery powered circuits.

Our push button switch also control positive side of the power supply using Sziklai Pair Configuration. So you can used this circuit for meal chassis devices. The Sziklai pair (compound pair) is a configuration of two bipolar (One NPN and One PNP) transistors, similar to a Darlington pair.

momentary push button soft latching toggle power on off switch circuit diagram

PARTS LIST
R1  1MΩ
R2  10KΩ
R3  100KΩ
R4  47KΩ (SEE NOTE)
R5  22Ω
R6  1KΩ
 C1  0.1µF (104)
C2  0.1µF (104)
C3  0.1µF (104)
C4 1µF 50V
Q1 2SD400
Q2 2SB507
IC1 CD4013

R4 must vary with supply voltage. Otherwise Q1 heat up or not proper bias Q2.

R4 ≈ (9×Supply Voltage)KΩ

Our push button switch circuit made using single flip flop. The output changes state every time flip-flop gets a positive pulse on the input.

The CD4013 IC contains two separate D-type flip flops and used one flip flop for our circuit.

CD4013 Dual D Type Flip Flop pin configuration cd4013BC

All mechanical switches has bounce when switching, the contacts make and break several times before switch on or off. This effect reduces by adding  C1, R1 and R6.

Fast switching on and off won’t work because the de-bounce circuit puts in a very small delay while C1 recharges through R1. It is not a problem in real life usage.

The circuit is off when it power up controlling by C2 and R2.

 

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2 comments on “Momentary push button soft latching toggle on off switch circuit
  1. Elliott Olson says:

    What is the maximum safe load current through Q2 using the 2sb507 (heatsinked or bare)?

  2. mk says:

    all time glade us

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