555 monostable setup

Please start with a simple description of what you want the relay to do with respect to any thing that might happen with the measured voltage input. Don't explain what this circuit does, just specify desired result. A timing diagram that shows the relay energized state, for brief and long pulses from measured voltage, on each side of the reference, would do it. Don't leave out possibilities, just because they don't matter. Show those times as don't care.

Use a capacitor to decouple it?

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
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Uh ?

How about using a brain to explain WTF you're talking about ?

Graham

Actually, the circuit was used to monitor the output a regulating PSU that uses 6x

2N3055 to get a higher output current. As the PSU was of ancient design, it sometimes shoot up to 27V from its normal 24V operating output. If the compararor detects 27V, it operates the relay and uses one of its SPDT contact to ground the bases of the 2N3055. The other contact is used to send earth to a 555 operating in monostable mode.

The monostable is suppose to send a 60 seconds positive going pulse to hold transistor Q1, so the PSU will remain OFF for 60 seconds. When the 60S delay expires, the relay releases and the 2N3055s will start to conduct again. If 27V is still there (which probably there wont be), an audible alarm will be sounded.

If the voltage exceeds 30V, another comparator will operate another relay and shut off the PSU completely and issuing an alarm.

HTH, thanks.

Allen

Only a little. Have you tried grounding these bases and releasing that ground, to see what the supply does?

Isn't it a problem to have the supply shut off for 60 seconds each time its output peaks at 27 volts or more? What if the operation of this pulses always generated another 27 volt overshoot, producing an endless stream of 60 second off times with brief 27 volt pulses between them?

This whole scheme seems too undercooked to merit time needed for a design.

Why not correct the design of the supply so that it doesn't produce 27 volt output unless it has a failed component?

how about you shutting the f*ck up and read the original post and maybe you'll see why I suggested it.

Any one that knows anything about the subject shouldn't question as to why I suggested it. I guess your not one of them.

Go back to your tea slurping and crumpet chewing session.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

How about you learning the meaning of decoupling ?

You regularly talk the most unadulterated crap ever.

Graham

Do you perhaps mean the OP should bypass the power source? It is what I assumed you meant in your first post. The stupid donkey shops for opportunities to be a nasty POS.

Of course, the power doesnt go to 27 volts all the time. It is more like an "if" condition. From what I understood, the PSU output only goes to 27V once in a blue moon. If it becomes 27V too often, say once in a week, I could set the threshold higher. If that still doesnt work I will scrap this part of the circuit and just maintain the >30V part which would surely work.

I did this circuit once to monitor the solar-cell-charged battery voltage on a remote station. The alarm was transmitted to our main office through radio. When the voltage dropped below 22V, it gave a "Battery Low" alarm. And if it is below 20V, it would issue a "Battery weak" alarm. But that design did not need to delay anything, so it was working well.

As you suggest, I would try to ground of the bases and see what happens at the output. Never though about that before.

Thanks

Allen

Try this:

Vcc Vcc \\ | | o o [10K] [10K] | | | | 2| | +----+---[.1uF]---+-----o NE555 | | Gnd

Insert a 10K and a .1 uF in your circuit between the relay point and the 555.

Ed

Ed,

I tried it out on a bread board and it works the first time.

Thank you very, very much !

Allen