SSR for speaker protection?

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#362
LKA said:
A short circuit can damage the mosfets in the SSR. (depending on the magnitude and duration of the current).
I want to warn everyone to use some current limiter and overcurrent detector in conjunction with SSR3.
The limiter current should be greater than the detector threshold current (which then activates the load/short disconnection).
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Sorry, I'm confused. I thought short circuit or over-current protection is something which is built into the power amp itself, if it is present at all? I've seen VI limiters in Randy Slone's books.

So, are you suggesting that it's unsafe to use these DC detect boards with amps which do not have such VI limiters? Can an over-current protection circuit be added to an amp externally?
 
#364
LKA said:
If it works, then no, but we can try to reduce some resistances. Did you use my PCB design ?
Click to expand...

On this case no.
I use my own pcb according to this schematic.
 

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#368
mosfet current rating when used in ssr

rhythmsandy said:
I have a doubt about it that the mosfets are rated at 120Amps now consider the pins of the mosfet upto what current ratings will those pins work without any issues? I mean the die of the mosfet might be able to deliver instantaneous or pulse currents of 120A but when it comes to sinusoidal waves what will be its capacity even though Vds is lower like about 3V or 4V max so when we check the SOA the device is capable of delivering the current but will the pins be able to deliver the current?

are you able to drive amplifier like +/-85V 500W into 4 ohms endup approx worse case current about 25Amp at an instance so will the pins be able to carry soo much of current?
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i did not see any reply to this question.
considering the irf135 mosfet, what audio current can it pass in the ssr application?
how do we use the SOA chart data when the mosfet is used as an ssr?
is the current ultimately limited by the devices pins?


https://www.infineon.com/dgdl/Infin...N.pdf?fileId=5546d462533600a4015364c38ddf29b1
 
#377
Here is the overload detection circuit connected.
Amplifier power supply is +/-50v
Power transistors are 3xA2223,3xC6145.
Emitter resistors are 0,22ohm.
What is the recommended,RS1 value?
I have choose 22ohm .
This is the value that activate the overload protection when amplifier go into hard clip for a long time.
 

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#378
""Choose RS1=100R (current limiter for IR led)
PC817 has forward voltage approx 1V. If RE=0.22R then Ith=1V/0.22R=4.5Ap
If you need higher current threshold, add RS2 (voltage divider).
RS2=100R Ith=9Ap, etc""
My found is against this.
What is the right?
Why a hard clipping amplifier need to operate for a long?
 
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