Keep MOSFET open using capacitor
Electrical Engineering Asked by Vladimir G. on February 24, 2021
I’m building a circuit that stays powered for some time after an additional power source is switched off.
+5V is always enabled but I only want LOAD to be powered when VCC (12V) is enabled and for some time (around 5 mins) after it is disabled. To achieve this I’m using a capacitor C1 which keeps NMOS open.
There are some questions:
- Is this circuit looks good enough or are there some issues here?
- R1 + R2 defines how fast the C1 discharges (and given the desired time, defines C1 capacitance). How big resistance can I choose for R1? I don’t really care about how fast it works but my guess is that with too big value it may fail.
Appreciate any help.
One Answer
Some assumptions were made by me during simulation, but the NMOS will gradually turn off after 375 seconds. It will take approximately 20 seconds to fully turn off under my simulated conditions. YMMV.
Correct answer by JonathanG on February 24, 2021
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