Designing a Delayed MOSFET switch Circuit for Voltage Transfer on a PCB

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DvirIL

Joined Nov 2, 2020
29
If I understand your requirements correctly, below is the LTspice sim of a simple circuit that should work for you:
The output turns on immediately (<2ms) (yellow and red traces) when the push-button is pressed (green trace) with about a 0.6s delay after the push-button is released.

Due to component tolerances, you may have to tweak the value of R3 (also could use a 500k pot in series with a 200kΩ resistor for R3) to get the off delay within your time requirements.
M2 can be just about any P-MOSFET with a ≥40V rating and an on-resistance of ≤50 milliohms.
C1 should be a ≥50V film type capacitor, not an electrolytic (aluminum or tantalum).
A ceramic cap may be acceptable, but they have poorer tolerance and temperature coefficient than film types.

If you want to control more than one MOSFET output from the same PB, just connect the additional P-MOSFET's gates to M1's gate.

(Edit: Added R5 to keep M2's Vgs below 20V.)

View attachment 302288
I'm look at your circuit again, and the position of PB not is what need to be designed, the "S" voltage pass or not pass the 24v so the PB should be before R4, and not all the charge/discharge times need to change, please tell me what you think
 

crutschow

Joined Mar 14, 2008
34,073
I'm look at your circuit again, and the position of PB not is what need to be designed, the "S" voltage pass or not pass the 24v so the PB should be before R4, and not all the charge/discharge times need to change, please tell me what you think
I don't understand the question.
 
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