There's no individual switches for power, so will be just when mains gets disconnected. The power supply is like a 'rack system' powering many modules.
One thing that I haven't mentioned is that I can't draw to much power for this as there's not alot going spare. Would like to keep it around 8mA across the whole 32V if possible.
(Apologies for not saying this earlier)
So the mosfet solution I think with the 1k would be more 30ishmA?
Sorry to keep banging on about this circuit.. but I'm not sure why this wouldn't work... https://i44.tinypic.com/ji25w4.jpg (+V being +16V and -V being -16V)
Any clues to enlightenment much appreciated!
The R1 and R2 can be increased and C1 decreased be a factor of X10. May not be a problem. I don't have a simulator or the time to bench test your original circuit. Maybe others can.
The R1 and R2 can be increased and C1 decreased be a factor of X10. May not be a problem. I don't have a simulator or the time to bench test your original circuit. Maybe others can.
Thanks.
Ah ok. Is that at the expense of 'reset' time?
I've uploaded the LTspice file of my original circuit if that's any help.
I'd try the thing in real for myself, but gotta order those relays from mouser (Im in UK) so have to order over £50 for free shipping. So I wanna make sure I'm on the right lines before commiting to an order.
Bit scared of surface mount! I don't mind doing an order from mouser if you think there's a good chance that the circuit will work. Tweaking of resistors, caps etc no problem. Or is it a flat 'that'll blow up' kind of thing?!
OK, I bench tested my circuit on a +/-15V supply with a 24V relay. The problem seems to be the time constant of R1 and C1 and your current limitation on R1. So, without an active element to discharge C1, it won't work with you limitations. If your circuit simulates OK, it may be the answer you started with.
OK, I bench tested my circuit on a +/-15V supply with a 24V relay. The problem seems to be the time constant of R1 and C1 and your current limitation on R1. So, without an active element to discharge C1, it won't work with you limitations. If your circuit simulates OK, it may be the answer you started with.
Thanks Ken. Thanks so much for doing that! Appreciate it!
Ok, I'll go with the circuit I have and hope for the best! Simulates fine. It's just I wasn't 100% sure that the anode of TL431 likes being on -16VDC (maybe it doesn't care) and as such whether the ref pin is 2.5V from the anode.
I guess the simulation would have shown up any problems if this was the case?
So if he wants the relay to operate when the voltage rises to +/- 16 Volt, then a voltage threshold detector would be better than a delay.
One way to do this would be to insert a 27 Volt Zener diode in series with the coil of a 5 Volt relay (with a normal diode across the coil - just to be sure to be sure).
Thus the relay will operate when the PS differential voltage rises to about 30 Volt, ie. 27 V + the relay operate voltage.
The relay will release when the PS is turned off and the diff voltage drops to about 28 Volt.
I assume that U1 is a SCR. I don't have a data sheet for it.
I feel that Q3 and some of the resistors could be removed.
My idea is that you can discharge C7 by connecting a capacitor from the switched side of the -16 V line to C7. Thus when the relay operates, C7 is discharged.
Then when the power is turned off, U1 goes open and the circuit goes back to its initial state.
You would need a diode across C7 to prevent it charging too far in the negative direction. It may even have to be a germanium or Schotty diode in order to minimise the reverse voltage.
Otherwise, U1 may be switched off by the negative potential. I would have to look at its data sheet to be sure.
I studied your circuit and now realise that U1 is a shunt regulator, not an SCR.
That is a novel idea.
Attached is my suggestion using an SCR.
C1 delays the operate of the relay by about 2 sec.
The 9V1 Zener prevents the trigger of the SCR until C1 has charged to about 10 Volt.
C1 starts discharging immediately the relay operates and needs about 13 sec to fully discharge. If that is too long, it could be reduced significantly by connecting a diode across R1.
This would reduce it to about 2 sec. It could be further reduced by reducing R2 to 10k.
The circuit can operate from either 16 Volt as shown or 32 Volt.
For 32 Volt I suggest that you would use a 22 V Zener and R1 could be reduced in value.
I don't know if this circuit has any real advantages over yours. But I've posted it anyway.