Other methods of converting a pushbutton switch to a latching/toggle switch (Zero power if off)

Thread Starter

blink13

Joined May 26, 2022
14
It's been days since I have been on this quest of making the pushbuttons that come with a electronics kit I bought to a toggle switch and although I have achieved it by using a NE555P IC Timer, I am not liking how it still consumes power even when the whole circuit is intended to be off. I am not turning anything on and off complex, just a resistor and an LED as the load because the key here is that I just want to make a toggle switch.

Here's what I've tried:
  1. Toggle switch using dual inverters with OpAmps (I like how the LM358P works with this) - But this one also consumes power even off and does not always work for some reason, sometimes it just stays on or off, not able to switch at times. Dual Inverter/Not Gate OpAmp Toggle Switch.​
  2. EEV Blog's Soft latch circuit - really nice circuit with few components, however, I don't have any MOSFET, so I used a BJT PNP transistor (2N3906). I can't get it to work because the PNP transistor is conducting current (Collector-Emitter) even if it's first powered on and its base is not grounded. I tried reviewing how a PNP works, hooked up the circuit again in a simulation with Falstad and NI Multisim live, same result, PNP is activated immediately after powering on even if I did not do anything. Scratched the circuit and went to try the simplest, with 555 timer.​
  3. I think this is the easiest of them all, just the 555 IC, 2 capacitors, and 4 resistors. However, it also seems it is consuming power even if it's turned off. The NE555P Method.​
I have not done:
Toggle/latching circuits that have some components I don't have such as Relays, CMOS IC and logic IC's (If I have to use logics I have to make them by hand with transistors, lol, I'll probably have to use all my transistor stock). I only have LM358P, NE555P, BJT Transistors, Resistors, and Capacitors.

I'd like to know other ways of doing such tasks with no power consumption on off or if it is even possible, help would be highly appreciated. :)
 

MisterBill2

Joined Jan 23, 2018
12,401
It is not really clear as to exactly what functionality you seek versus what the two buttons provide. If they are an O/OFF function, then what is wrong with that? If they momentarily switch on two different functions that is a separate issue.
So an explanation of what is present and what is desired is needed to avoid a lot of guesses.
 

Thread Starter

blink13

Joined May 26, 2022
14
It is not really clear as to exactly what functionality you seek versus what the two buttons provide. If they are an O/OFF function, then what is wrong with that? If they momentarily switch on two different functions that is a separate issue.
So an explanation of what is present and what is desired is needed to avoid a lot of guesses.
Oh,
What is done/available already:
  1. 2-button toggle switch, one for on, and other for off.
  2. 1-button toggle switch (2 stable modes with one switch) done with the 555 timer
What is desired:
  1. When the circuit is off (switch circuit), there should be no current or power use. Like, If I do not intend for the load to be turned on then there should be no current on circuit.
  2. 1-button toggle switch using a pushbutton switch. Because my current switch is a momentary one.
  3. Only use BJT transistors and other discrete components such as resistors, capacitors, diodes.
 

MisterBill2

Joined Jan 23, 2018
12,401
OK, now it is clearer. Most electronic alternate action schemes consume some current in both the on state and the off state. ALL logic IC schemes consume some current in all conditions.
The challenge with many latching circuits is that they are not alternate action arrangements, or that they are rather complex.
If the item being switched on and off is battery powered then power consumption is certainly a concern, while a mains powered system can often accept a bit of increased power draw.
There do exist alternate action push-button switches, I have several devices that include them. That would certainly be the very simplest way to meet the requirements. Such devices exist in a wide spread of package sizes and prices, but may not be available in local distribution. I suggest looking at the Digikey website catalog for examples.
 

crutschow

Joined Mar 14, 2008
30,103
With your limited supply of components, I don't see how you would make a zero-power latch circuit.
You will need to buy some P-MOSFET or CMOS parts for that
 

Thread Starter

blink13

Joined May 26, 2022
14
All right, I get now that the desired outcome cannot really be achieved with what I currently have. And from what I have been reading it'll be complex or even if I did, I would not even be able to achieve all the desired feature.

What I got from here is:
  1. Best done mechanically with a switch made for such purpose.
  2. Use P-MOSFETS
  3. Logic ICs (I think CMOS is part of it)

Now at least I won't be bound by the idea and I can move on, lol. I'll try to get my hands on them and start looking how are they used for such purpose. I was really inclined with the idea because the mentioned components takes a while to arrive and pricey.
Thanks all!:)
 

vu2nan

Joined Sep 11, 2014
251
Hi blink13,

Here's how a lamp could be toggled on & off using an SCR (Thyristor) and two momentary push button switches.

123.png

No power is consumed when the lamp is off.

This AC version uses a Triac.

1.png

Nandu.
 
Last edited:

AnalogKid

Joined Aug 1, 2013
10,096
EEV Blog's Soft latch circuit

I think this one is workable. changing the pass transistor to a PNP requires adding a base current limiting resistor to the driver transistor collector. Other than a few nA of leakage current in the transistors, I don't see any off-state current paths.

Note that the circuit relies on a low impedance to GND at its output in the off state to discharge the debounce timer capacitor and assure that the pass transistor driver is off. It should have two additional resistors to make the circuit's operation independent of the output load.

Another option is a 2-gate latch with CMOS logic gates. As above, there are no current paths in the off state except leakages. Both the gate input currents and the chip's static current are in the nA range. Not 0.00000000000 A, but still . . .

ak

Latch-Toggle-1-T8W8e.png
 
Last edited:

MrSalts

Joined Apr 2, 2020
1,832
Define "zero current".
logic chips that consume under 1 microamp will last for 10s to 100s of years on a battery (that is, well beyond the self-discharge lifetime of a battery). Is that zero? Or do you mean, literally "zero". If so, why is zero a requirement?
 

Thread Starter

blink13

Joined May 26, 2022
14
Define "zero current".
logic chips that consume under 1 microamp will last for 10s to 100s of years on a battery (that is, well beyond the self-discharge lifetime of a battery). Is that zero? Or do you mean, literally "zero". If so, why is zero a requirement?
My god, take it as a stupid idea of mine. Haha, I meant like the power consumption is like it's in sleep/hibernation so it is negligible in the long run on times where the load is not mean to be powered.

But yea, I did get pointed out that it is an impossible idea beacuse even so, there'd be a current of ~0.0000..01.
 

MisterBill2

Joined Jan 23, 2018
12,401
The concept I see with truly "zero" current is that there is no logic state being maintained, and so if the power is removed and then replaced a day later the logic state will not have changed. FFs and counters and some register devices will not always power up in a predictable manner. Sometimes that matters.
That is why low-power (low Iq) devices are not touted as Zero power. And if there are a hundred of the devices it may matter even more.
 

BobaMosfet

Joined Jul 1, 2009
2,000
It's been days since I have been on this quest of making the pushbuttons that come with a electronics kit I bought to a toggle switch and although I have achieved it by using a NE555P IC Timer, I am not liking how it still consumes power even when the whole circuit is intended to be off. I am not turning anything on and off complex, just a resistor and an LED as the load because the key here is that I just want to make a toggle switch.

Here's what I've tried:
  1. Toggle switch using dual inverters with OpAmps (I like how the LM358P works with this) - But this one also consumes power even off and does not always work for some reason, sometimes it just stays on or off, not able to switch at times. Dual Inverter/Not Gate OpAmp Toggle Switch.​
  2. EEV Blog's Soft latch circuit - really nice circuit with few components, however, I don't have any MOSFET, so I used a BJT PNP transistor (2N3906). I can't get it to work because the PNP transistor is conducting current (Collector-Emitter) even if it's first powered on and its base is not grounded. I tried reviewing how a PNP works, hooked up the circuit again in a simulation with Falstad and NI Multisim live, same result, PNP is activated immediately after powering on even if I did not do anything. Scratched the circuit and went to try the simplest, with 555 timer.​
  3. I think this is the easiest of them all, just the 555 IC, 2 capacitors, and 4 resistors. However, it also seems it is consuming power even if it's turned off. The NE555P Method.​
I have not done:
Toggle/latching circuits that have some components I don't have such as Relays, CMOS IC and logic IC's (If I have to use logics I have to make them by hand with transistors, lol, I'll probably have to use all my transistor stock). I only have LM358P, NE555P, BJT Transistors, Resistors, and Capacitors.

I'd like to know other ways of doing such tasks with no power consumption on off or if it is even possible, help would be highly appreciated. :)
Oh,
What is done/available already:
  1. 2-button toggle switch, one for on, and other for off.
  2. 1-button toggle switch (2 stable modes with one switch) done with the 555 timer
What is desired:
  1. When the circuit is off (switch circuit), there should be no current or power use. Like, If I do not intend for the load to be turned on then there should be no current on circuit.
  2. 1-button toggle switch using a pushbutton switch. Because my current switch is a momentary one.
  3. Only use BJT transistors and other discrete components such as resistors, capacitors, diodes.
Do you know what an SCR is?

One button could trigger the SCR, the other button can disconnect it. You can fake an SCR with two BJTs.
 
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