'Deadman Oscillator'

May 03, 2016 4 Replies

Rate this thread:

dagmargoodboat 10 years ago

I had a recent need to reset and retry something until it succeeded, but only after a certain delay.

My solution--

I vetted several more complex topologies before settling on this-- along the lines of a watchdog timer, but with the ability to retry ad infinitum, this circuit is normally held off by Q1's conduction. A fault condition cuts Q1 off. C1 then charges for a start-up delay time, which in my application filters out transients.

Once V(Ct) reaches Vth+, U1 commences oscillating, providing periodic reset pulses until the FAULT condition successfully clears.

.--[Rt]--. | | | |\ | .----+---| >o-+----> RESET* | | |/ U1 'hc14 |/ [Ct] FAULT* >-[R]-| Q1 | |>. === | ===

Cheers, James Arthur

Vote

rickman 10 years ago

I guess it is obvious that if the fault control can't be cleared in time to avoid the next reset, it will never come out of fault. Or is fault generated by a different circuit than the one being reset?

Rick C

Vote

dagmargoodboat 10 years ago

You're correct. The oscillator "high" period has to be longer than the fault recovery time.

In my actual circuit a diode+Rt2 leaves the RESET*=high time long, and sets t(RESET*=low) short.

Cheers, James Arthur

Vote

Jim Thompson 10 years ago

R-U-S: Reset Until Smoke ?>:-} ...Jim Thompson

Vote

dagmargoodboat 10 years ago

Not likely. The protection is very aggressive, shuts down quickly. But there's no human supervision, so once the fault's cleared the system needs to be able to get up off the ground and recover on its own.

Cheers, James Arthur

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required