Optocoupler Speaker Protection

benproiii · 29th June 2011, 06:57 PM

can someone please check this circuit over before i order the parts,
it should short out the power supply rails of the amp if dc in on the speaker output.

Bensen · 29th June 2011, 07:09 PM

You are using a diac with a breakover voltage of 32V? This seems a factor +-60 to high in my eyes.

The Ulti Amp from Elektor uses the same idea to shortcircuit the rails. They have shorted the rails to the ground.

See post #4
Elektor's "Ulti Amp"

Gr.

benproiii · 29th June 2011, 07:22 PM

Do you know a substitute that has a lower breakdown voltage?

Mooly · 30th June 2011, 06:28 AM

What if the offset is negative ? The LED in the triac won't conduct.

Also DC offset protection should trip even with a low offset of only a couple of volts or so.

benproiii · 11:57 AM

Is this better?

janneman · 30th June 2011, 03:22 PM

Quote:

Originally Posted by benproiii

Is this better?

I think conceptually it will work, but I'm not sure the switch-point is well defined. You don't want it to switch unnecessary.
What is the threshold voltage of that bidirectional thing?
There's also the real chance that one rail fuse blows before the other, and you end up with one rail active and that's probably worse than the offset.
If you do it this way, use two triac one for each rail to gnd.

jan didden

benproiii · 30th June 2011, 04:38 PM

how bought this?

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29th June 2011, 07:09 PM	#2
Bensen diyAudio Member Join Date: May 2003 Location: Belgium, Limburg, Bree	You are using a diac with a breakover voltage of 32V? This seems a factor +-60 to high in my eyes. The Ulti Amp from Elektor uses the same idea to shortcircuit the rails. They have shorted the rails to the ground. See post #4 Elektor's "Ulti Amp" Gr.

29th June 2011, 07:22 PM	#3
benproiii diyAudio Member Join Date: Aug 2010	Do you know a substitute that has a lower breakdown voltage?

30th June 2011, 06:28 AM	#4
Mooly diyAudio Member Join Date: Sep 2007	What if the offset is negative ? The LED in the triac won't conduct. Also DC offset protection should trip even with a low offset of only a couple of volts or so. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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