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'Deadman Oscillator'

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

Reply to
dagmargoodboat
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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
Reply to
rickman

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

Reply to
dagmargoodboat

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

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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Reply to
Jim Thompson

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

Reply to
dagmargoodboat

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