I'm designing a shutdown circuit that switches off a SMPS regulator after a 10 second time interval.

This is a battery powered application and the battery voltage could be anywhere between 7-15V.

I've looked at capacitor circuits and 555 timers and it seems to me that their timing will be dependent on the input voltage supplied - is this correct?

I just need a very simple IC with a pin that goes high 10 seconds after a switch is pressed, where the timing is independent of the battery voltage.

Regulating the voltage is not an option - I already have a regulator in the circuit and I'm trying to switch it off!

Any suggestions would be greatly appreciated, thanks in advance!

  • 4
    \$\begingroup\$ A 555's timing is not significantly dependent on the supply voltage. \$\endgroup\$ – brhans Jan 7 at 2:02
  • 1
    \$\begingroup\$ As long as the battery voltage powering the 555 doesn't change much during the interval. If the battery severely sags under load and that changes during the interval it would probably cause some timing variation by breaking the relationship between integrated current resulting from historic voltage and the threshold based on the current voltage. But this doesn't sound like a precision application. Or you can use a regulator or have an MCU count crystal oscillator periods. \$\endgroup\$ – Chris Stratton Jan 7 at 2:28
  • \$\begingroup\$ where the timing is independent of the battery voltage. You should define how much independency you need. Do you always need exactly 10,000 seconds? I don't think you do. I think anything between 8 and 12 seconds will do just fine. A 555 timer can do that easily. So don't ask for / worry about dependencies without first thinking about what you actually need. \$\endgroup\$ – Bimpelrekkie Jan 7 at 10:20
  • \$\begingroup\$ You could also use a very low power 555 circuit fed by a regulator that accepts those voltages. 555+7805? \$\endgroup\$ – K H Jan 8 at 0:11

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