Re: Turn off delay circuit

Jamie wrote:
Look for the 555 timer, It has 2 inputs, trigger and threshold that are
part of a RS (Reset/Set) flip flop circuit.
Pulling the trigger low will latch the output on, pulling the
threshold high will unlatch the output. etc.

It's smaller and more versatile than employing a flip flip chip when
you only need one switch. On top of that, you can also place some timing
activity in that same lay out.

Sorry I really did not phrase my question well it seems. By "power on" and "power off", I meant really the power to the circuit, maintaining power while needed and cutting its own power after the desired action has been performed. It is intended to save as much power as possible when the circuit doesn't do anything.

A 555 circuit would not do since it would need to be powered on permanently.

That's why I said a FET would do. Probably any other transistor, but the FET is closer to my energy saving goal. Here's what I imagined :

.------------------------.
VCC o-+------+ +----+ |
| --- | "Slave Circuit" |
| ^ | |
| | | |
| / | | Something here keeps |
+--/ o--+----+ the FET conducting |
| | as long as needed. |
.-. | |
| | | |
| | | |
'-' | |
| | |
| | |
GND o----------+----+ |
'------------------------'

When the user presses the switch, the circuit is powered and in turn pulls the FET gate up. The user can release the switch at this time. At some other time in the future, the circuit decides it does no longer need power and lets the gate go down, cutting power and hopefully consuming zero current. I need to figure out if this would work and what kind of transistor to use.

vic.
.

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