Hi power supply users,
Here is an old trick which should be in use in the series pass regulated
supplies or could be added with little effort. Actually, I will list two
modifications for supplies.
The output filter capacitor if you detect by measurement is not acting as a
big enough current reservoir, can have another cap of same or higher voltage
rating paralleled with it.
But in a series pass regulator, when you have a zerner circuit in the base of
the pass transistor, there is supposed to be a filter cap there also. Its
capacitance will be effectively multiplied by the Beta of the Pass transistor,
and thus, you could increase the base filter and do wonders for the output as
well. In the old Atlas radios, they had a three terminal regulator for the
VFO that did not include the base capacitor. That resulted in Atlas drift if
the mobile voltage sagged as was the case with old battery and car not
running. Adding the capacitor improved the regulation. Even 10 MF was a good
improvement at the base of the regulator. Observe proper polarity, and don't
be confused by the cathode of the zener, which is opposite to the circuit
polarity needed.
The above info on Beta multiplying the cap value is found in the old Motorola
Zener diode handbook, a very useful theory book and practical info on power
supply regulation.
73, Stuart K5KVH
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