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Old 13th August 2003, 07:20 AM   #1
Eccu is offline Eccu  Finland
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Default Will this DC protection work?

http://www.astro.uu.se/~marcus/private/dcprot.jpg



Yes... and my Crescendo is still under construction.
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Old 13th August 2003, 07:26 AM   #2
sajti is offline sajti  Hungary
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It looks OK.

Sajti
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Old 13th August 2003, 08:55 AM   #3
moamps is offline moamps  Croatia
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Hi

Segment around PNP transistor isn't correct. IMHO
PNP transistor never acts like transistor.

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Old 13th August 2003, 09:20 AM   #4
sajti is offline sajti  Hungary
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The PNP will works as switching diode if the amplifier's output going to negative DC.

Sajti
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Old 13th August 2003, 09:24 AM   #5
moamps is offline moamps  Croatia
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Quote:
Originally posted by sajti
The PNP will works as switching diode if the amplifier's output going to negative DC.

Sajti

Then, use diode !?!
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Old 13th August 2003, 09:41 AM   #6
sajti is offline sajti  Hungary
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Quote:
Originally posted by moamps



Then, use diode !?!

Yes, and increase the 1kohms resistor, to get better sensitivity.

Sajti
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Old 13th August 2003, 10:37 AM   #7
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A quite common solution is to use two NPN transistor for this detection circuit. One is connected in common emitter like the left one an the other one is connected in common base with the base to ground and the input diode to it's emitter.

It doesn't cost a lot to build the detection circuit for both cannels seperately because there is a DC failure mode (which might of course occur very seldom) that this circuit can't detect: If one output goes fully positive and the other one fully negative the circuit wouldn't recognize it !!!

Regards

Charles
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Old 13th August 2003, 11:59 AM   #8
moamps is offline moamps  Croatia
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Quote:
Originally posted by phase_accurate
[B]A quite common solution is to use two NPN transistor for this detection circuit. One is connected in common emitter like the left one an the other one is connected in common base with the base to ground and the input diode to it's emitter.
]
I agree. I use diode bridge, then NPN. Work ok.

Quote:
It doesn't cost a lot to build the detection circuit for both cannels seperately because there is a DC failure mode (which might of course occur very seldom) that this circuit can't detect: If one output goes fully positive and the other one fully negative the circuit wouldn't recognize it !!!
Than sense resistors can't be equal. (22k and 10k will be OK)

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Old 13th August 2003, 01:06 PM   #9
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Quote:
Than sense resistors can't be equal. (22k and 10k will be OK)
Congrats for this idea.

Charles
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Old 13th August 2003, 01:10 PM   #10
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Quote:
Originally posted by moamps

Than sense resistors can't be equal. (22k and 10k will be OK)

hehehe good point

BTW I love this simple circuit, I think I'm going to use it too in the future.

best regards,

HB.
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