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SSR for speaker protection?
SSR for speaker protection?
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Old 18th February 2018, 05:54 PM   #11
Mooly is offline Mooly  United Kingdom
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SSR for speaker protection?
This explains the operation of the FET's in one of my amps. (I know it will mean something to you )

First image is the FET relay with a floating voltage source between G and S.

Second image is the FET passing a small AC signal.

Third image is an even smaller signal. The red trace is the junction of the FET's

Forth image is showing the Vgs voltage under higher drive conditions.
Attached Images
File Type: jpg SSR1.JPG (161.6 KB, 674 views)
File Type: jpg SSR2.JPG (177.1 KB, 674 views)
File Type: jpg SSR2B.JPG (174.5 KB, 643 views)
File Type: jpg SSR3.JPG (179.7 KB, 623 views)
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Old 18th February 2018, 06:00 PM   #12
fvzeppelin is offline fvzeppelin  Germany
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Quote:
Originally Posted by Mooly View Post
This explains the operation of the FET's in one of my amps. (I know it will mean something to you )

First image is the FET relay with a floating voltage source between G and S.

Second image is the FET passing a small AC signal.

Third image is an even smaller signal. The red trace is the junction of the FET's

Forth image is showing the Vgs voltage under higher drive conditions.
Very impressive
Typical AB power stage
Interested in details of my strange project?
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Old 18th February 2018, 06:10 PM   #13
Mooly is offline Mooly  United Kingdom
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SSR for speaker protection?
Thanks The amp is kind of a work in progress... you know what its like

By all means post up your project if you want to.
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Old 19th February 2018, 11:22 AM   #14
hahfran is offline hahfran  Germany
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make it easy. Mains switched via relay or triac. E.g. by remote control. To avoid power on thumb a relay shorts output to ground via 10 ohms. The amp state control - dc control etc. then opens the relay and it is out of the signal path. In case of failure it turns off mains triac and shorts supply of amp via triac with a few ohms series resistor. Fast enough to protect speaker.
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Old 19th February 2018, 05:29 PM   #15
fvzeppelin is offline fvzeppelin  Germany
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Quote:
Originally Posted by hahfran View Post
make it easy. Mains switched via relay or triac. E.g. by remote control. To avoid power on thumb a relay shorts output to ground via 10 ohms. The amp state control - dc control etc. then opens the relay and it is out of the signal path. In case of failure it turns off mains triac and shorts supply of amp via triac with a few ohms series resistor. Fast enough to protect speaker.
Thank you for your suggestions!

Actually, I have a crowbar already in place But I intend to use the output switch for
- cases when I don't want to blow the fuses, e.g. overtemp
- avoidance of "plopps"
- (redundancy)
I assume that these cases can be handled either way, using mechanical or solid state relays - both having advantages and disadvantages. I personally prefer the SSRs for their better lifetime and silent switching.
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Old 11th November 2018, 02:11 AM   #16
cakyol is offline cakyol  United States
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Hi LKA, do you sell these protectors ? I would consider buying them :-)
I am building an amp abut 500 watts rms/channel at 8 ohms.
So, supply is about +/- 92 volts dc and speaker current can be up to 10 - 15 amps
peak.
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Old 11th November 2018, 10:33 AM   #17
LKA is online now LKA  Europe
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Quote:
Originally Posted by cakyol View Post
Hi LKA, do you sell these protectors ? I would consider buying them :-)
I am building an amp abut 500 watts rms/channel at 8 ohms.
So, supply is about +/- 92 volts dc and speaker current can be up to 10 - 15 amps
peak.

Hi, no, I do not have any board for selling. Also, my implementation is for maximum 200W. You will need better mosfets (or heatsink) and other detector circuit.
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Old 11th November 2018, 11:37 AM   #18
Trollet is online now Trollet  Sweden
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SSR for speaker protection?
I have tested with IRFP360 because I have a bunch of them.
It seems to work, but what are the importnant parameters for this application?

Low RDSon, enough VDS and ID ?
With lower RDSon there will be less heat produced to?

BR

Figge
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Old 11th November 2018, 05:11 PM   #19
Mooly is offline Mooly  United Kingdom
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SSR for speaker protection?
Low Rds is important for high current applications. The IRFP360 is 0.2 ohms which is pretty high when you compare it to other devices, but that FET scores on voltage and current ratings.

I used IRF2907's which have an Rds of just 4.5mΩ and a 75 amp Ids although they have a much lower voltage rating of 75 volts.
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Old 11th November 2018, 05:52 PM   #20
Trollet is online now Trollet  Sweden
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SSR for speaker protection?
Well, as I thougt then
As I've got plenty of the 360's for free they may be good enough för now.
Voltage and current ratings seems ok för a bigger amp, but needs a little more coling.

I also got IRF064 with 0.009 ohm RDSon, but only 55 volts VDS. May be good for smaller amps.

Tested with TLP591 as driver but VGS may be ~7 volts, so using two in series maybe garantees that they give maximum. Also use a Jfet to cut VGS faster, but don't know If it's really nessecary

Best Regards

Figge

Edited Swedish auto correction. It s***s....

Last edited by Trollet; 11th November 2018 at 05:56 PM.
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