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Old 30th August 2011, 09:48 PM   #1
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Default Determining current limit

If you have 2 pairs of 16A, 250W TO-3 Lateral FET's with a SOA curve showing a maximum DC current of around 6A at 42V Drain-source what would a reasonable current limit be set to?

There is no 100ms or 10ms SOA plot for the Semelab BUZ line of FETs that I'm planning to use.

I know they are Laterals so they have their own "built in" current limiter due to their negative temp co but in my case I am using flying catch diodes to limit the maximum Vgs. Which of cource means that I also have a current limit.

Double the amount of flying catch didoes in the diode string from 1 to 2 which gives me a current limit of around 12-13A so that is very close to their specified DC current in the SOA plot.

However, for music would it not be reasonable to set the current limit a little higher, say 20A instead? Just needs another pair of diodes and I'm at 20A. 20A with a music signal should be well within the limit of 2 pairs of 16A, 250W, TO-3 Laterals.

Any thoughts and/or suggestions?

Last edited by Neutrality; 30th August 2011 at 09:51 PM.
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Old 31st August 2011, 07:12 AM   #2
djk is offline djk
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Most laterals are about 1A per volt of gate voltage. Clamp the gates at 10V and use a thermal cut-out at 85C, that should be enough.
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