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.
| 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.
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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Please send your ideas, which are very important for our success…
all time glade us
What is the maximum safe load current through Q2 using the 2sb507 (heatsinked or bare)?
Thanks it wocks
Really useful circuit, thanks. Works great.
One question – what is C4 for? what does it do?
Thank you
Hi,
Great little circuit – I have been looking for this for some time.
I will be using this switch circuit to switch a Lithium Ion 3.7V/4.2V battery pack.
Due to space constraints I will have to use SMD devices.
Do you know the equivalent surface mount devices for Q1 and Q2?
Can C4 be a ceramic capacitor?
Many thanks.
What happens when the switch is closed and held closed indefinitely? Will the output remain in its transferred state?
Hi there,
Can I use other transistores?
NC
May I have your permission to use this circuit in my Electrical Engineering Senior Design Project?
Hello, I have successfully built this circuit into a device that controls 2 switching functions from a momentary pushbutton on the front panel. I simply copied the design to the other side of the CD4013. One of the 2 ‘virtual switches’ needed to default to ON position.
You can attain this by leaving Pin 1 unconnected, and connect R4 to pin 3 of the IC. This way, instead of the normal output, you use the complementary output which is always inverse.
Please note that R3 also remains connected to the complementary output (Pin 2). If you connect R3 to pin 1 the flip-flop function doesn’t work anymore. I made this mistake and learned from it 🙂
Because you feed back the inverted output, the flip-flop will see the inverse state of its current position at the data input, and switches to that inverse state as soon as the clock is triggered.
can we change the power up mode to the previous mode it was in?
Could you please modify the circuit to replace the 2 transistors with a mos fet so greater loads can be switched without increasing the physical size of the circuit board
Regards Denis