[Noisebridge-discuss] N00b question - changing power supply voltage

[jim]

   a dc-to-dc converter! great idea. given the 
description of the "pelt", probably no conditioning 
is needed other than possibly switching noise 
backing up into and possibly through the supply 
(i.e. the non-load side of the converter). 

   as to practicality, there's weird stuff and a 
variety of smallish electronics suppliers that 
usually specialize (audio, music, ham radio...) 
that might have a 12VDC transformer with sufficient 
current capability--that and a couple of diodes 
might be enough. for a transformer you might take 
a look at local electrical suppliers (e.g. b and k 
on division or maltby's on 7th near folsom). 





On Fri, 2010-07-02 at 10:08 -0700, davidfine wrote:
> 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-
> 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 http://en.wikipedia.org/wiki/Autotransformer  Using a
> transformer to convert DC involves more circuitry. 
> 
> 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. 
> The potentiometer or voltage divider solution is not so good because
> you'd need beefy parts and output varies based on load. 
> 
> A dc-to-dc converter is a switching converter as opposed to a linear
> regulator:
> http://en.wikipedia.org/wiki/DC-to-DC_converter
> A switching converter is the best choice for high current, here's the
> relevant paragraph from wikipedia:
>         In these DC to DC converters, energy is periodically stored
>         into and released from a magnetic field in an inductor or a
>         transformer, typically in the range from 300 kHz to 10 MHz. By
>         adjusting the duty cycle 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 switched-mode power supply. Many
>         topologies exist. This table shows the most common.
> 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. 
> --D
> 
> 
> On 7/1/10 1:57 PM, Sean Cusack wrote: 
> > Hey kids -
> > 
> > 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?
> > 
> > Sorry if this one is likely obvious - but everyone can blame Mitch
> > for getting me way to into electronics for my own good :).
> > 
> > Sean
> > 
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> >   
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