BOSOZ's PSU runs very very hot

[ruangrit]

The PSU seems to work fine with no connection to the Pre circuit.

Once I connected the PSU to the Pre circuit (no signal fed yet), the FET Q101 and Q102 started to run very very hot (could not touch after 5-6 minutes).

On the Pre circuit everything seemed to be OK, all FETs were warm, I got voltage at G, D, S accourding to the document (approx. +31 at Drain pin and 3.X at Source pin).

I have also noticed that the PSU voltage dropped to +58.XV (did not measure the -voltage as I had to switch the circuit off).

By the way, there are a couple of changes I have made (1) to the zener pack to obtain +-60V (2) 2200uF/100V and 100uF/100V instead of 1000uF and 10uF accordingly.

The transformers are 2 x 35-0-35/600VA but I do not think this will produce any problem.

Any thoughts on this heat problem...??

[audionut]

If I remember correctly...q101 and q102 are part of the regulator...I feed 4 channels of BOSOZ from these regulators and the Mosfets run very hot, and so I put them on large heat sinks. It took a lot of heat sink to get the temp to 50C

[SvErD]

You probably have 100v+ out off your rectifiers wich means you regulators have to drop 40v. You definately need some heat sinking.

[ruangrit]

You are right, I got 111V at the BR, although the PSU has to drop >40V I thought this is what each zener pack does though.

Correctme if I'm wrong.

By the way, I have tried with a bigger heatsink (considered big comparing to the size of the PSU.

Not sure if those who have posted their bosoz pictures with small heatsink would experience the PSU heat problem as such or not.

Thanks,
RR.

[eLarson]

The zener diodes will establish the Gate voltage, with the Source voltage being about 4 volts less than that. The Drain, though, is attached to the unregulated voltage (about 111, I think you said.)

So, yes, you will probably want to some hefty heatsinking to prolong the life of the MOSFETs.

Erik

[Charles BL]

I'm Running approx 90V into my PS and yes the Mosfets get warm. Would I be better off to increase the zener stack and regulate to more like 75-80V than 60? Can the bosoz take it?
Thanks
Charles BL

[ruangrit]

You are right Erik, I've really overlooked this...I better drop off the Drain voltage in stead of trying to adjust the heatsink size...

Any suggestion? if I maintain the 2 x 35-0-35 transformer.

One quick way is to replace the transformer to 2 x 24-0-24 where I can easily find "ready to use" product locally. This will supply Drain voltage less than 70V...However, I should be able to maintain the output at +-60V...

Thanks,
RR.

[eLarson]

I'd probably just intersperse some resistors among
your filter caps to drop the raw supply down some.

You could throw in a choke, too, if you're so inclined.
As long as the total resistance (including that of the
choke) is more than

2* sqrt ( L / C) where L is in henries and C is in Farads,

then you wouldn't have to worry about any nasty
peaks.

Erik

[ruangrit]

Thanks Erik, I'll try this coming weekend...

[jh6you]

Originally posted by ruangrit
One quick way is to replace the transformer to 2 x 24-0-24 where I can easily find "ready to use" product locally. This will supply Drain voltage less than 70V...However, I should be able to maintain the output at +-60V...

With 2 x 24V transformer, I would try to get +/-50V using 6 x 9.1V zeners.

JH