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The practical thing to do is to buy a big 12V supply for $5 on ebay.
But that's less fun to think about so-<br>
It's actually easier to transform AC voltages (with a transformer) and
then put the output through a DC rectifier. Then you could use
something like <a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/Autotransformer">http://en.wikipedia.org/wiki/Autotransformer</a> Using a
transformer to convert DC involves more circuitry. <br>
<br>
For a high current operation like this (12v x 4.5a = 54 watt), you
don't really want to use a linear converter (something that dissipates
excess energy as heat) You *could* use a battery of linear rectifiers,
or you can buy a dc-to-dc converter on an IC which is actually a
different beast. <br>
The potentiometer or voltage divider solution is not so good because
you'd need beefy parts and output varies based on load. <br>
<br>
A dc-to-dc converter is a switching converter as opposed to a linear
regulator:<br>
<a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/DC-to-DC_converter">http://en.wikipedia.org/wiki/DC-to-DC_converter</a><br>
A switching converter is the best choice for high current, here's the
relevant paragraph from wikipedia:<br>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
<blockquote>In these DC to DC converters, energy is periodically stored
into and released from a <a
href="http://en.wikipedia.org/wiki/Magnetic_field"
title="Magnetic field">magnetic field</a> in an <a
href="http://en.wikipedia.org/wiki/Inductor" title="Inductor">inductor</a>
or a <a href="http://en.wikipedia.org/wiki/Transformer"
title="Transformer">transformer</a>, typically in the range from 300
kHz to 10 MHz. By adjusting the <a
href="http://en.wikipedia.org/wiki/Duty_cycle" title="Duty cycle">duty
cycle</a> of the charging voltage (that is, the ratio of on/off time),
the amount of power transferred can be controlled. Usually, this is
done to control the output voltage, though it could be done to control
the input current, the output current, or maintain a constant power.
Transformer-based converters may provide isolation between the input
and the output. In general, the term "DC to DC converter" refers to one
of these switching converters. These circuits are the heart of a <a
href="http://en.wikipedia.org/wiki/Switched-mode_power_supply"
title="Switched-mode power supply">switched-mode power supply</a>.
Many topologies exist. This table shows the most common.<br>
</blockquote>
So yah, you need a circuit to control the duty cycle of the input
voltage, a transformer, and perhaps some circuitry to smooth the
output. <br>
--D<br>
<br>
<br>
On 7/1/10 1:57 PM, Sean Cusack wrote:
<blockquote
cite="mid:AANLkTikNP6Fz5zCKN1YB0XJvnKw9cgbjlN4jgomkL929@mail.gmail.com"
type="cite">Hey kids -<br>
<br>
So, I've got a relatively simple dilemma that I sure pops up all the
time for those of you that are way better at electronics than me. I've
got a power supply providing a fixed 24V @ 4.5A, but I only want to use
12V of that for my circuit. I originally thought I could lower the
voltage using a potentiometer, but because the power is so high, they
all cost some serious bank. Is there another (not necessarily analog)
solution to changing voltage and/or amperage through a circuit that is
cheap to build?<br>
<br>
Sorry if this one is likely obvious - but everyone can blame Mitch for
getting me way to into electronics for my own good :).<br>
<br>
Sean<br>
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