3

FORGE

a good idea is to cut a piece of its original plastic case

(they will have the same size and thus fit tightly) and

use it as a bracket, glueing it to the enclosure.

The final step is to install all the external elements

on the front panel: switch, potentiometer, digital

LED voltmeter and banana plugs (to provide the

output voltage to the banana cables), as well as the

laptop adapter 220 VAC input on the back or on one

side of the case. As a finishing touch you can add

a potentiometer knob cap, so it’s easier to turn it to

select the desired output voltage and, why not, it

looks much nicer!

YOU’LL NEED

Plastic enclosure

(or your own hand

made case)

Laptop power

adapter

DC-to-DC voltage

reduction

module

Digital LED

voltmeter

10 kΩ

potentiometer

Potentiometer

knob cap

Switch

Banana plugs

Banana cables

Wires

Heat shrinkable

cable sleeves

Figure 3

Variable power supply schematic

Figure 2

Heat shrinkable cable sleeves are highly recommended to avoid

undesirable electrical contacts

limitation). You should first carefully desolder the tiny
potentiometer and then solder back a regular 10 kΩ
potentiometer, which can be handled easily from the
exterior of the power supply enclosure.
After removing the plastic case of the laptop power
adapter, solder its output wires to the input of the DC-
to-DC voltage reduction module through a switch, so
that the power supply can be turned on and off.
A digital LED voltmeter (again something that you
can get for £1–£2) is connected to the DC-to-DC
voltage reduction module and shows the selected
output voltage to the user. The voltmeter used in this
project is able to provide a readout of voltages from
2.5 to 30 VDC with 1% accuracy.
Now it’s necessary to fit everything into an
appropriate enclosure, to have all the components
safely connected and be able to transport the power
supply wherever you fancy. The DC-to-DC module can
just hang from the wires to which it’s soldered, but
be careful to isolate it properly if you use a metallic
enclosure. To fix the laptop adapter to the enclosure,

CONTENTS MAY BE HOT

Safety advice: be careful handling the DC-to-DC

voltage reduction module while it’s functioning, as

some of its components (especially the DC-to-DC step-

down converter) may become very hot. Make sure that

it says cool enough not to damage your enclosure, and

that there’s nothing that could catch fire.

8.8.8

+

-

AC IN DC OUT

(^100) 50v
RVT
220
SVK35v
470
LM2596
Vin-
Vout-
Laptop
Power
Adapter
Original
potentiometer
removed
Vin+ Vout+
Below
Everything wired up
and ready to power
your next project
Digital LED
voltmeter