Hi, from Ken,
"rob34" wrote in message
...
Paul Burridge wrote:
On Mon, 20 Oct 2003 11:20:20 -0400, rob34 wrote:

2N3055 are great, but 2N3771 are better! Rob

2N3773 are better still ( check out current ).

If you want a power supply to deliver round about 40amps the the first thing
to remember is that you MUST have the correct amount of pass transistors to
handle the current.
If you use 2N3055's ( very good and cheap ) you will need at least 10 of
these, don't think for one minute becouse you see the current stated as
being 20amps that one transistor will be able to handle this amout of
current, it won't, it does not work like that.
The best you can hope for ( current wise ) from one 2N3055 is FIVE AMPS. So
for a forty amp supply you would need at least, eight and a couple for that
le-way we all try to allow.

One other thing you must have good heat sinks.

Regards the transformer, it should be able to handle the current and should
( ideally for a 13.8Volt supply ) be rated between 17.5 and 18.5 Volts of
load.
Once regulated this voltage will rise to about, 24 Volts + or - 1 or 2
Volts.

Regards regulation the most common way is to use the LM723 voltage regulator
chip complete with short circuit protection.

Smoothing caps should be another point of concern.
Try to find two large ripple handling units rated at about 40 Volts and
allow two thousand mfd
per one amp of current required.

One final point to remember when building your own power supply is to use
some form of ELECTRONIC OVER-VOLTAGE PROTECTION ( I.e., the MC3423 chip is
perfect ).
The number of cheap commercial power supplies on the market without
overvoltage protection fitted is a crime ( but they never tell you this in
the Ads..right..?. ).

Hope the above helps in some small way. Good luck, Ken, G4KIR.



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