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connecting dc supplies in parallel for more current

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October 29th 03, 10:09 PM

Paul Keinanen

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On 29 Oct 2003 10:16:56 -0800, (clc) wrote:

For a regulator use a 7815 IC to drive several 2N3055's. ARRL
handbooks have a good example of 2N3055's in parallel. 5 2N3055's on
a decent heatsink will run nice and cool. Scrounge for heatsinks,
too. They tend to be cheap at hamfests because most people are
appliance operators.

A 7815 would give 15 volts, wouldnt that be alittle high? A 7812 would be a
little low, so i thought of a 723 ang just adjust the voltage to 13.8.

The Vbe for the 2N3055 is quite high, it might be well over 1 V at
some larger current. Thus, the output voltage would be under 14 V and
with some emitter resistors to share the load between the transistors
even less than that.

Nominally, the 7815 can only supply 1 A and assuming worst case hFE
for the 2N3055 of 20 at 4 A, the output current would only be 20 A, so
five 2N3055 devices would nicely give 20 A. If more current is needed,
more series pass transistors are needed, but the 7815 is not capable
of supplying the required amount of base current, so a driver
transistor is required between the 7815 and the series pass 2N3055
transistors. With two Vbe drops, the output voltage would be 13 V or
less.

Paul OH3LWR

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