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Old 19th May 2013, 08:08 AM   #21
dadod is offline dadod  Croatia
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Originally Posted by michaelkiwanuka View Post
Dadod, I think you use a regulated power supply? There is no need for a regulated power supply for power amps.

The idea I proposed is to have solid state switches in the unregulated supplies of the amp. to disconnect them from the amp. in the event of SOA violation or DC offset.
Yes it is a regulated but not with fix output voltage. It is more similar to capacitance multiplier, output follows slow input voltage changes. Capacitance multiplier doesn't need big capacitance bank and semicondactors are cheaper then big capacitors. Power dissipation lost on the regular is relatively small(needs no more then 5 V of voltage drop for proper funtion). Then it was quite easy to integrate all needed protection(it is not current limiter but current dependent current delayed fuse).
BR Damir
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Old 19th May 2013, 08:20 AM   #22
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Has anyone considered SOA protection in which the protection transistors are removed from the forward path of the amplifier and, instead, opto-coupled to a bistable which drops out the output relay?

The protection locus would have to be conservative as it would have to accomodate the fact that it may take up to ten milliseconds to drop out the relay.
This is what I use; the actual activation of the relay is done through a uP7331 (IIRC the number).

jan
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Old 19th May 2013, 11:52 AM   #23
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Originally Posted by michaelkiwanuka View Post
Can those relays be used to turn off the supply rails instead of having them in series with the output?
I proposed to use opto-coupled trench FETs to isolate the power rails to the amp after I saw Andrew's solid state speaker relay.
Seems like an excellent idea for home audio.
- Protect the speaker and the amp with one circuit.
- No relays to fail or weld shut.
- No fuses to fail or replace.
- Eliminate any possibility of tedious debate about the effect of the FET in series with the speaker.
Didn't have much response, most people just reproduce the old speaker relay idea.
I plan to use this in my next amp.

Best wishes
David

Last edited by Dave Zan; 19th May 2013 at 11:57 AM.
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Old 19th May 2013, 11:58 AM   #24
AndrewT is online now AndrewT  Scotland
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I have already "tested" a prototype for the -ve supply rail. It uses Nchannel and is easily triggered with a two transistor Thyristor to latch it "OFF".

I have not worked up a +ve rail version that can use the same Nchannel device without a higher voltage +ve supply rail to give the Vgs across the switching N mosFET.
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Old 19th May 2013, 12:21 PM   #25
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I have already "tested" a prototype for the -ve supply rail. It uses Nchannel and is easily triggered with a two transistor Thyristor to latch it "OFF".

I have not worked up a +ve rail version that can use the same Nchannel device without a higher voltage +ve supply rail to give the Vgs across the switching N mosFET.
Use photo-voltaic couplers to drive the FETS. Then you can use the better FETs in both rails.

Best wishes
David
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Old 19th May 2013, 12:30 PM   #26
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Another option would be to use a small floating DC-DC converter like in this example. Makes for a truly floating switch which can be used anywhere.


jan
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File Type: pdf ss switch-1.pdf (19.0 KB, 77 views)
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Old 19th May 2013, 04:04 PM   #27
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Originally Posted by jan.didden View Post
This is what I use; the actual activation of the relay is done through a uP7331 (IIRC the number).

jan

Jan, you'll recall I simulated your triple slope protection arrangement and showed that it doesn't work as you intended.

Is the uP7331 latching? If it's not it will turn the relay on and off instead of dropping it out permanently untill power is cycled.
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Old 19th May 2013, 05:37 PM   #28
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Originally Posted by michaelkiwanuka View Post
Jan, you'll recall I simulated your triple slope protection arrangement and showed that it doesn't work as you intended.

Is the uP7331 latching? If it's not it will turn the relay on and off instead of dropping it out permanently untill power is cycled.
Yeah I never was able to reconcile your sims with my build unit, which seems to follow the intended curve as far as I could measure.

That uP chip can be set to switch off and only switch on again as power is recycled (it has an AC power sensing also) or (with a jumper) to make it close the relay when the overload is no longer there, after a setable delay. That is the setting I normally use; I have it 're-try' every 2 secs or so.

jan
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Old 25th May 2013, 06:15 PM   #29
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These MOSFET drivers look promising:

Data Sheet - ASSR-V621 and ASSR-V622, Dual Channel Photovoltaic MOSFET Driver (6.5V/15μA) (95 KB)
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Old 27th May 2013, 02:03 PM   #30
JPV is offline JPV  Belgium
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I have implemented and tested open circuit on full power 50V on 4 ohms with a short circuit on the 4 ohms, only a small spark on the shorting wire; Works great.

two circuits on switch (with pnp or npn logic and dc or ac capabilities) and one short circuit detector with latch
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