DC-Protect Circuitry - Page 3

parsecaudio · 4th September 2006, 10:11 AM

Hi jacco
If the op amp are correctly used,they are very high reliable.
Never i view a op amp failure in normal work conditions.
In more years of designing,two times an op amp of my project had fails:during a thunderstorm(1 op amp over 5 in a preamp first time and 3 over 5 during the second thunderstorm).
Do not preoccupe for the reliability of this circuit:the first I built is in 1984 and it work today:never i have made any substitution

selfservice · 4th September 2006, 10:44 AM

what about using mosfets instead relay?
unuseful? unreliable? unnecessary?

Fritzell · 4th September 2006, 02:34 PM

I'm building a mosfet-circuit that brakes DC-supply voltage from the poweramp when protectioncircuit sends a protect signal (V+)
Schematic:

The good thing is that mosfets are faster and more reliable than relays because there is no mechanical function. Also Relays for big DC-currents are expensive and takes a lot of space..

http://files.upl.silentwhisper.net/upload6/Amp_PSU.pdf

I'm gonna etch the PCB for this circuit today and someday this week the components will come so I can't tell yet if it works good or not though.

4fun · 4th September 2006, 03:44 PM

Quote:

Originally posted by Fritzell
I'm building a mosfet-circuit that brakes DC-supply voltage from the poweramp when protectioncircuit sends a protect signal (V+)
Schematic:

The good thing is that mosfets are faster and more reliable than relays because there is no mechanical function. Also Relays for big DC-currents are expensive and takes a lot of space..

http://files.upl.silentwhisper.net/upload6/Amp_PSU.pdf

I'm gonna etch the PCB for this circuit today and someday this week the components will come so I can't tell yet if it works good or not though.

Hi Fritzell!

Your circuit looks promising, I was worried about RDSon but to my surprice it was almost in level with a relay.

anatech · 4th September 2006, 04:31 PM

Hi 4fun,

Quote:

I was worried about RDSon but to my surprice it was almost in level with a relay.

That will vary with current load and dynamics. Somehow I don't like this idea. Just a feeling thinking about how the power supply will interact with high performance amplifier circuits.

However, give it a shot!

-Chris

4fun · 4th September 2006, 05:59 PM

Hi Anatech!
Some large caps after mosfets would slow down things over mosfets somewhat and keep impedance low but also carry a hefty charge in case of failure.
If I have to choose myself I want as low rail impedance as possible with good quality caps very close to last stage.

I tend to agree with you, but as you say, give it a try.

AndrewT · 4th September 2006, 06:20 PM

Hi,
is a FET in line to the amp worse than a fuse? Both will show an effective resistance with the attendant volts drop. Both will modulate the voltage arriving at the amp in time with the current pulses.

What about the alternative if semiconductors in line are so abhorent.
Use the in line fuses followed by a pair of FET crowbars.

How easy to design this circuit?

Back to that PDF.
is K1 an opto isolated thyristor?

What limits the voltage on the 470uF delay capacitor?

4fun · 4th September 2006, 07:07 PM

Hi!

Quote:

Use the in line fuses followed by a pair of FET crowbars.

Nice and brutal, I like it!

AndrewT · 4th September 2006, 07:39 PM

Hi,
yes brutal and fairly quick and all it costs is two fuses.

But, can it be made as simply as the FET disconnectors? shown in post23 PDF, just 12 components.

latala · 4th September 2006, 08:04 PM

I dont like the power fet protection at all
We are after spk protection if a fet fails for whatever we have DC
No good !!!
I prefer the crowbar but I have found that end users will try to defeat these (bigger fuses)
I have used the crowbar a few times
To me the best method is to bite the bullet and use a high power Relay/Contactor.
I normally use a circuit the gives me a time delay before connecting the spk (no switch on thump).
I then use a circuit to monitor the dc offset so that above a few volts and a time of no more than 0,2 sec the contactor is forced off.
The advantage here is that if there is a dc offset(thump) on switch on the spk is not connected !!
So virtually any device can fail and the spk is safe! I know this may seem primitive but to be honest I have seen many devices fail in the feild despite sophisticated protection ideas
As for the Mosfet ideas there,s nearly enough parts to build a spare amp.
best regards Trev

4th September 2006, 05:59 PM	#26
4fun Enjoy good sound diyAudio Member Join Date: Aug 2005 Location: In the middle of Sweden	Hi Anatech! Some large caps after mosfets would slow down things over mosfets somewhat and keep impedance low but also carry a hefty charge in case of failure. If I have to choose myself I want as low rail impedance as possible with good quality caps very close to last stage. I tend to agree with you, but as you say, give it a try. __________________ / Anders

4th September 2006, 06:20 PM	#27
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, is a FET in line to the amp worse than a fuse? Both will show an effective resistance with the attendant volts drop. Both will modulate the voltage arriving at the amp in time with the current pulses. What about the alternative if semiconductors in line are so abhorent. Use the in line fuses followed by a pair of FET crowbars. How easy to design this circuit? Back to that PDF. is K1 an opto isolated thyristor? What limits the voltage on the 470uF delay capacitor? __________________ regards Andrew T.

4th September 2006, 07:39 PM	#29
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, yes brutal and fairly quick and all it costs is two fuses. But, can it be made as simply as the FET disconnectors? shown in post23 PDF, just 12 components. __________________ regards Andrew T.

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4th September 2006, 10:11 AM	#21
parsecaudio diyAudio Member Join Date: Apr 2004 Location: ventimiglia	Hi jacco If the op amp are correctly used,they are very high reliable. Never i view a op amp failure in normal work conditions. In more years of designing,two times an op amp of my project had fails:during a thunderstorm(1 op amp over 5 in a preamp first time and 3 over 5 during the second thunderstorm). Do not preoccupe for the reliability of this circuit:the first I built is in 1984 and it work today:never i have made any substitution

4th September 2006, 10:44 AM	#22
selfservice diyAudio Member Join Date: Jul 2004 Location: italy	what about using mosfets instead relay? unuseful? unreliable? unnecessary?

4th September 2006, 02:34 PM	#23
Fritzell diyAudio Member Join Date: Jul 2004 Location: Sweden	I'm building a mosfet-circuit that brakes DC-supply voltage from the poweramp when protectioncircuit sends a protect signal (V+) Schematic: The good thing is that mosfets are faster and more reliable than relays because there is no mechanical function. Also Relays for big DC-currents are expensive and takes a lot of space.. http://files.upl.silentwhisper.net/upload6/Amp_PSU.pdf I'm gonna etch the PCB for this circuit today and someday this week the components will come so I can't tell yet if it works good or not though.

4th September 2006, 08:04 PM	#30
latala diyAudio Member Join Date: Feb 2006 Location: staffordshire	I dont like the power fet protection at all We are after spk protection if a fet fails for whatever we have DC No good !!! I prefer the crowbar but I have found that end users will try to defeat these (bigger fuses) I have used the crowbar a few times To me the best method is to bite the bullet and use a high power Relay/Contactor. I normally use a circuit the gives me a time delay before connecting the spk (no switch on thump). I then use a circuit to monitor the dc offset so that above a few volts and a time of no more than 0,2 sec the contactor is forced off. The advantage here is that if there is a dc offset(thump) on switch on the spk is not connected !! So virtually any device can fail and the spk is safe! I know this may seem primitive but to be honest I have seen many devices fail in the feild despite sophisticated protection ideas As for the Mosfet ideas there,s nearly enough parts to build a spare amp. best regards Trev

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