555 on/off single push button latching circuit

Thread Starter

Nordle

Joined Jun 20, 2018
10
Hello,
i want to make a switch for small electric vehicles (ebikes for example)
i want a single push button to turn on and off power, just a n-fet in my case

after i searched and found a circuit i could understand and adapted it to my needs i came up with this:
circuit.png
I would like to add another feature, to turn off the button should be held for a small amount of time so it couldn't turn off accidentaly.
But i have no idea how to achieve this, i'm not very experienced, learned what an opamp is a week ago and today about 555 timer:)

Cheers
 

crutschow

Joined Mar 14, 2008
31,151
Here's the LTspice simulation of a fairly simple circuit that should do what you want.
It requires one D-FF and one Schmitt trigger inverter.
C1 provides a delay for the MOSFET turn-off with no delay for the turn-on.
C4 and R5 provide debounce protection (changes state only once even if the switch contacts bounce).
C2 and R3 set the switch to off during power-up.
Notice there is no turn-on delay but about a 1 second turn-off delay.

upload_2018-7-4_21-28-51.png
 

Thread Starter

Nordle

Joined Jun 20, 2018
10
i tried to replicate this in everycircuit but am a bit stuck, there are no schmitt trigers and my flip flop is missing 2 pins?
i tried to make the schmitt trigger out of an opamp just for the simulation, would that be right? and where do i connect the voltage source?

Nordle_circuit (2)_corr.png

Moderators note : inverted image vor better visibility
 

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crutschow

Joined Mar 14, 2008
31,151
The missing FF pins are for Set and Reset, and are not needed in this circuit.

The op amp Schmitt trigger is problematic, depending upon what the maximum open-loop output voltage of the op amp is.
That circuit has hysteresis when the voltage is high, but no hysteresis when the voltage is low.
For simulation purposes you can just use a standard inverting gate, even if it does not have hysteresis.
In real life you will need one with hysteresis to avoid possible oscillations and false triggering.

The voltage source is to power the FF and gate.
 

Thread Starter

Nordle

Joined Jun 20, 2018
10
thanks crutschow, i think i’ll just built one and try it out:) i can’t make it work in everycircuit..

what do you think would be the best solution to pwer this from a 42V battery?
I would just use a resistor and a zener to keep it simple, but ideally there should be as less current draw as possible in off state.
 

crutschow

Joined Mar 14, 2008
31,151
what do you think would be the best solution to pwer this from a 42V battery? I would just use a resistor and a zener to keep it simple, but ideally there should be as less current draw as possible in off state.
You could use an LM317HV high-voltage linear regulator to generate 5-12V (or whatever voltage you want) for the system.
The LM317HV will take 12mA output minimum quiescent current with no load.
(Make R1=100Ω to provide a path for that current.)

For lower quiescent current, you could make a series regulator with an N-MOSFET and a zener diode.
 
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