You should check the unregulated /loaded/ voltage first.  Draw five amps
from it and see what the voltage is.

Chances are good that the voltage will drop significantly when loaded
with 500mA or so, and your regulators will be able to handle the large
voltage drop (suitably heatsinked, of course).  As the current
consumption goes up, the transformer voltage will drop and the regulator
will not have to drop so much voltage (though it will still be
dissipating more power).

-Adam

Ed Edmondson wrote:

>Hello,
>
>I was going to build an adjustable power supply with an output of 1.25 to 26
>volts at 5 amps maximum. The transformers I ordered came in and the rectified
>and filtered output is 39.5 volts and I had calculated for 28 volts.
>
>I was going to go ahead and use the transformers as the are as I am only
>building two power supplies. I was wondering if a preregulator with a 2N3055
>transistor, a 27 volt 1 watt zener diode and 1N4750A (27 volt, 1 watt, Izt =
>9.5 mA nominal and 34 mA maximum) and a 1200 ohm half watt resistor (between
>the collector and base) would drop the extra 11 volts I have?
>
>I calculated this from a web site tutorial on zener diodes and pass
>transistors. Since the problem with the transformer I don't want to have the
>same problem with this preregulator circuit.
>
>Aside from the heatsink I will require are these assumptions correct? If
>someone would double check this I would be grateful.
>
>Thanks,
>Ed
>
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>
>
>
>
>
>
>

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