3

Build a variable power supply

TUTORIAL

Get electrons into your circuits with the correct energy.

Build a variable

power supply

f you are tinkering with electronics, soon or

later you will need to power your projects

with different DC voltage levels. We show

you how to easily build your own variable

power supply.

When starting to play around with electronics,

many people power their prototypes directly from

controller boards, such as an Arduino. However, as

the prototypes become more complex (e.g. with the

addition of servos or motors), they soon require more

power than these controllers can safely deliver. At this

point, you’re going to need a variable power supply

that can provide different voltage levels. Of course

you can buy such a power supply, but it’s a piece of

cake to build one yourself.

A good starting point to build a variable power

supply is a laptop power adapter. These adapters

normally provide relatively high output voltage and

Ricardo

Caja Calleja

funwithcables.wordpress.com

An aerospace engineer

by profession, Ricardo

is deeply interested

in robotics and

automation. If there’s

nothing to repair at

home, he’ll make up

some plan to build

anything that includes

cables or screws.

ampage. So just rescue an old laptop adapter from

gathering dust at home, and you’re ready to go. The

adapter used in this project provides 19 VDC and

almost 2 A, more than enough to power most of the

prototypes you’ll ever work with.

ONE STEP BEYOND

As the laptop adapter provides a fixed amount of

output voltage (19 VDC in this case), you will need

some device that “does the magic” of reducing the

DC voltage to lower levels. The best option for this

purpose is an DC-to-DC voltage reduction module that

includes the LM2596 DC-to-DC step-down converter.

It costs about £2 and supports an input voltage of

up to 35 VDC and 3 A. This module comes with a

tiny 10 kΩ potentiometer for regulating the output

voltage, which can vary between 1.25 VDC and 35

VDC (19 VDC in this case, due to the laptop adapter

I

Figure 1

All the elements are

packed in a practical

case that can be

easily carried around

Depending on the

specifications of

your laptop power

adapter and the

DC-to-DC module,

the minimum amount

of output voltage will

vary. This means that

you won’t be able to

obtain voltages below

~1.25 VDC.

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