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G 30th October 2002 11:15 AM

Using a dropping resistor in Zen V4 unregulated supply.
Hello all,

I have a power transformer that has two 43 volt windings on the secondary and each winding is rated at 1kva. Would there be a problem with adding a 5 ohm 50 watt dropping resistor in the unregulated supply for a Zen V4, or can I just use the 60 volts and change the biasing of the circuit?


Mad_K 30th October 2002 01:22 PM

as long as you have enough heatsinking, you could have higher rail voltage and bias with more power output of the circuit. Watch the dissipation for the mosfets though. paralell fets if you want to go really high on the bias.

I would recommend to use one secondary winding for each channel, add a zener in the regulator, and use 2A bias.

G 30th October 2002 02:52 PM

Thanks mads!


miguel2 30th October 2002 04:17 PM

Hi G,

I am using 45V on secondaries and I am burning all the voltage in the PSU MOSFET. So I am using a IRFP240 there. It works OK as long as you have heatsinks.

Do not let the higher unregulated voltage reach the regulated rail. I burned one chanel this way (around 65V on the drain of Q2).

I wonder if a zener of about 45 - 50 V on the regulated rail does any good preventing this.

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