[Collins] Bench supply for MP-1

[Dr. Gerald N. Johnson, electrical engineer]

Connect one of the secondaries in series with the primary to buck the
voltage and get the output voltage down to something reasonable. 22
volts each side of center means about 31 volts unregulated. And that
means for every watt of load power you waste a watt in the pass
transistors. NOT EFFICIENT!!! Dropping the primary with the 44 volt
winding bucking gets the unregulated down under 21 volts. So you only
waste a half a watt for each watt of load.

You need a lot of voltage drop in the emitter equalizing resistors to
keep the pass transistors sharing properly. Probably a volt drop at full
load. 

I prefer to regulate in the negative lead with N type MOSFETs. They
don't need equalizing resistors and can regulate down to .02 volts drop. 

When using pass transistors I prefer to use NPN in the negative lead
with a LM320K-12 adjusted for a little higher voltage. I put the
LM320K-12 on the same heatsink as the pass transistors and arrange the
circuit so the LM320K-12 gets to supply much current at the power supply
limit so the LM320K-12 supplies current limiting and pass transistor
temperature protection.

I have scans of both schematics. The bipolar circuit has a couple
decades of use, the MOSFET on has run here for 3 or 4 years, 24/7
running my station and packet node. I use a 12 volt each side of center
power supply with the MOSFET, but that is a hair low. I need (even with
Schottky rectifiers) about another volt to allow for transformer and
diode drop at currents above 30 amps. I use a 750 VA 12/24 volt
buck/boost transformer.

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.