Time Delay Relay Circuit

[tetwin11]

We have a circuit where a 5V control signal is used to turn on a MOSFET. I'd like to add a circuit in between here that, when the control goes high, the output signal that our MOSFET controls goes high for a prescribed amount of time (~5s) then goes back low. I have a circuit drawn that I think has some promise. I borrowed heavily from online resources. But it seems like a bit much, so I wanted to throw it out there to see if anyone has some other/better concepts of how to do this. Thanks in advance!
p.s. Vbat in the schematic is 20-30V, 24V nominal.

 

[tetwin11]

I just found this circuit that might simplify what I was trying to do, but still uses the 555 concept.

http://www.learningaboutelectronics.com/Articles/555-timer-delay-before-turn-off-circuit.php

 

[Comcokid]

The type of circuit you are looking for is called a monostable circuit or one-shot and can be built from a 555 timer (or from a lot of other chip choices). I did not look closely at your schematic but you shouldn't apply the control to the LM78M12 ground. All you're going to do is switch your regulator from not regulating to regulating. Setup the 78M12 normally. Look at 555 monostable circuits on line and apply the on/off control there.

 

[tetwin11]

Thanks for the reply. I think I understand what you're saying. I don't want to put a drain on Vbat when the 5V control signal is not present, so that is what I was attempting to do.

 

[tetwin11]

My plan is to use a lower power ICM7555 and run it off of the 5V control signal. That way there will be no draw on the battery when off and fewer parts! Just needs an RC filter on the trigger to keep it low for a while at startup then bring it high before the timer runs out. Thanks for the help, I hope this works!