12v speed control lamp dimmer
circuit can be used as a speed controller for a 12V motor rated up
to 5A (continuous) or as a dimmer for a 12V halogen or standard
incandescent lamp rated up to 50W. It varies the power to the load
(motor or lamp) using pulse width modulation (PWM) at a pulse
frequency of around 220Hz.
SILICON CHIP has produced a number of DC speed controllers over
the years, the most recent being our high-power 24V 40A design
featured in the March & April 2008 issues. Another very popular
design is our 12V/24V 20A design featured in the June 1997 issue and
we have also featured a number of reversible 12V designs.
Circuit looks like:
For many applications though, most of these designs are over-kill
and a much simpler circuit will suffice. Which is why we are
presenting this basic design which uses a 7555 timer IC, a Mosfet
and not much else. Being a simple design, it does not monitor motor
back-EMF to provide improved speed regulation and nor does it have
any fancy overload protection apart from a fuse. However, it is a
very efficient circuit and the kit cost is quite low.
There are many applications for this circuit which will all be based
on 12V motors, fans or lamps. You can use it in cars, boats, and
recreational vehicles, in model boats and model railways and so on.
Want to control a 12V fan in a car, caravan or computer? This
circuit will do it for you.
The circuit uses a 7555 timer (IC1) to generate variable width
pulses at about 210Hz. This drives Mosfet Q3 (via transistors Q1 &
Q2) to control the speed of a motor or to dim an incandescent lamp.
While the circuit can dim 12V halogen lamps, we should point out
that dimming halogen lamps is very wasteful. In situations where you
need dimmable 12V lamps, you will be much better off substituting
12V LED lamps which are now readily available in standard bayonet,
miniature Edison screw (MES) and MR16 halogen bases. Not only are
these LED replacement lamps much more efficient than halogen lamps,
they do not get anywhere near as hot and will also last a great deal
Silicon Chip 15 November 2008