design a Time delay circiut

[purpleanger]

Hi,

I'd like to design a circuit such that at first, the circuit is completely powered off. The user pushes a switch, which injects power into the circuit. Then a mechanism maintains the power active, even if the switch has been released. At a later about 3 seconds, when the circuit does no longer need power,
it cuts its own power and sleeps until the user chooses to push the
button again.

How can i design this circuit, do not use 555 timer.
Because of i wanna integrated this circuit in smart card.

Thanks.

 

[muthukumar_ece2004]

You may use Super charge capacitor to keep the supply voltage up to 3Sec. depending upon the time, capacitance value may get change!

This is just a idea, we have to take care on designing the capacitor value and this is for simplicity.

 

[eklikeroomys]

Proximity sensor?

 

[leo_o2]

Use R & C to generate the delay?
1Mohm * 1uF=~1S.

 

[KerimF]

Did you consider using a counter IC which has an internal oscillator as CD4060?

Kerim

 

[purpleanger]

Thank about your reply Kerim

Tell me more information about that? please.
Thanks.

 

[KerimF]

Thank about your reply Kerim

Tell me more information about that? please.
Thanks.

I assume you can get its datasheet (the IC is a standard CMOS one).
Unfortunately I can't have one to test what we will talk about.

First, it is very important to know the state of all outputs of the counter. I hope, but I am not sure, that the IC resets itself (all outputs become low) anytime it is powered. But if the outputs will have a random state at a start then I am afraid we need to let its reset pin do the job much like we do for resetting some MCUs. In this case a capacitor (could be very small since the input is CMOS) is connected between Vcc and the reset pin (11) also a high value resistor between the pin and ground. So when Vcc is applied, the charging current of the capacitor will rise the pin voltage for a short time resetting all outputs.

Could you check this?
Please note that in case the IC can always reset itself at powerup pin 11 should be grounded.

Kerim