13.8V/40A Stabilized Power Supply
provided by: John - wat69 (EA3KE) - wat69arsystel.com
This power supply was designed for ham-radio use and has been in
operation for over 10 years.
Its design is very simple and practically immune to RF. It is assembled
from discrete components, being the most costly element a 600VA toroidal
transformer, which can be replaced by another with different
characteristics, provided it has a voltage of between 17~20V and the
right power for our needs.
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The reference voltage is obtained from a 7.5V Zenner diode (6V8 ~ 8V2)
applied to Q2 which compares the voltage output by the resistive divider
formed by R5, VR2 and R6, controlling the Darlington amplifier Q3 which
is responsible for driving the output stage consisting of driver Q4 and
4 NPN power transistors 2N3771, which can be mounted directly to the
heatsink without being isolated, because its collector is connected to
The source has maximum current limiter (Q1) adjustable via VR1 and
overload indicator LED (DL2) and total protection against short circuit,
with zero consumption in case of short circuit, can be maintained in
this state indefinitely without danger.
(Keep in mind that due to the high power of the PSU a occasional short
with a high length or small section cable that has sufficient strength
not to exceed the maximum current of 40A. Might not be considered a
short circuit and cause the PSU supplying a high amount of power).
The power rectifier diodes (D1, D2) are recommended metallic threaded
type with the cathode grounded, mounted on a large enough heatsink
isolated from the chassis. For the power transistors using a heatsink as
big as possible, without being isolated as discussed above, may be part
of the aluminum chassis of the box. We also recommend the use forced
ventilation with a thermostat.
I wish you every success.