Another simple DC protection

[tiefbassuebertr]

what about this approach?
http://www.diyaudio.com/forums/solid-state/155939-mosfet-relais.html

 

[portreathbeach]

R5 & R6 bring down the offset current to non damage levels.
The two resistors allow just 1.1mA to pass from 50Voffset to the good channel.

Of course. 44Kohm resistance between left and right output. This seems a lot simpler than the first schematic I posted with all of the diodes, and obviously the FET will hold it self on until the power is removed, therefore no need for a PIC at all.

The gate of Q2 is connected to ground! How can this ever switch?

And can +25v be used instead of 12v?

 

[jony]

The gate of Q2 is connected to ground! How can this ever switch?

Q1 detects positive dc voltage.
And Q2 detects negative dc voltage.
To switch ON Q2 you need 0.6V between base and emitter.
So If we connect base of a Q2 to GND (0V) we need -0.6V on emitter to switch ON Q2.

C1 provides soft-start and C2, C3 can be replaced by one electrolyte capacitor because all electrolyte capacitor can handle -0.7V for a short period of time.

And can +25v be used instead of 12v?

yes you can.

 

[portreathbeach]

Thanks very much jony.

 

[Mooly]

Hi Hugh,
Thanks for the compliment... one of these days I might actually get around to a new amp build... and then take this further.

The 6.8meg and 47pf roll the HF off considerably. I went for such values to avoid any possible criticism that the circuit loads the volume pot at all, or could introduce any non linearity.

Thanks...

 

[portreathbeach]

jony, I built the circuit. When I power it, the relay energizes. When I put + or - volts to the input, the relay clicks off and stays off even when I remove the + or - from the input. So it seems to be working..... Now, to reset the circuit, the power needs to be removed and then re-applied. When I do this, it takes forever for the relay to energise. If I remove the 2 x 47uF caps, everything works the same and the circuit resets immediately after the power is applied.

Is this normal?

 

[portreathbeach]

Ok. I'm not sure what is actually going on....

I have a 1meg resistor as in the original diagram, connected to a 1uF cap. and 2x 10uF caps connected in reverse where the 47uF caps are in the diagram.

When I first connect, there is a slight delay and the relay energises.

When I put + or - onto the input, the relay de-energises (OK so far)

I remove the + or - and after 4 or 5 seconds, the relay energises again, shouldn't it stay de-energised until I cycle the power on and off to it? (Or am I getting MOSFETS and Thyristors mixed up her?)

 

[jony]

When I first connect, there is a slight delay and the relay energises.

This delay is cause by C1

I remove the + or - and after 4 or 5 seconds, the relay energises again,

seems OK for my.

shouldn't it stay de-energised until I cycle the power on and off to it?

To achieve this you need softly modify the schematic

 

[portreathbeach]

Thanks jony, as I said in my previous post, I got MOSFETS mixed up with SCRs.

Cheers for the schematic, very similar to circuits we use in control systems at work, with the relay holding itself on when energised.

 

[sregor]

One minor catch in setups with both amps feeding the circuit through a resistor. (This actually happened to me in an old Nikko reciever). I had one output go to the positive rail, and the other going to the negative rail, and the protect circuit had zero volts goin in, so it energized the relay!. (Problem was due to broken ground connections on the input wires going into the circuit board.) Murphy's law in action.

 

[Alex Kotov]

My simple protection:

 

[Bonsai]

referering to post 38, Q2 and Q3 connection, is risky since any board leakage or noise can lead to problems.

 

[portreathbeach]

Just in case anyone wants to have a look, here is a link to a page from the chip amp photo thread of my Gainclone:

http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery-137.html

 

[susannsusann]

A second amp with such DC protect there is - also from elektor. Title "The Current Amp" Nov/Dec 1992. Load impedance: 400 mΩ load and 35A peak output current. Also available in french:
http://209.85.129.132/search?q=cach...current+Amp"+elektor&cd=5&hl=de&ct=clnk&gl=de
(scoll down)

hallo tiefbassuebertr,
hast du eventuell den Schaltplan vom Current Amp aus 92, der Link geht leider nicht, besten dank.
LG susannsusann

 

[planet10]

hello tiefbassuebertr,
You may have the circuit diagram of current amplifier from 92, the link is not live, thank you.
LG susan Susan

English please

dave

 

[susannsusann]

OK, thanks

 

[Ulis]

My DC protection

 

[susannsusann]

hello Ulis,
thanks, but my current Amp is broken and i search a circuit from this Elektor current amplifier from 11/12 1992
many thanks

 

[terranigma]

Q1 detects positive dc voltage.
And Q2 detects negative dc voltage.
To switch ON Q2 you need 0.6V between base and emitter.
So If we connect base of a Q2 to GND (0V) we need -0.6V on emitter to switch ON Q2.

C1 provides soft-start and C2, C3 can be replaced by one electrolyte capacitor because all electrolyte capacitor can handle -0.7V for a short period of time.

yes you can.

Hello all,

Regarding to circuit at post #37, can i connect more than two channels each with 22k resistor additionaly via proper relay?

Thanks.

 

[AndrewT]

Yes extra 22k input resistors allow the detect to monitor extra channels.

But beware.
If you get opposite polarity fault signals, they can cancel out and the detector sees nothing wrong.

Further, as one adds extra channel/s the sensitivity drops.