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On 10/25/2010 7:17 AM, Invisible wrote:
> 1. Why do you need several different voltages?
Different components require different voltages. Sometimes you get lucky
and everything will run all one a single voltage. You may have high
intensity LED's that have a voltage forward of more than 3.3 volts, so 5
volts is a logical choice to power the backlight circuitry allowing the
LED's to function, but pumping 5 volts into a chip requiring 3.3 volts,
would possibly overheat at best or fry at worse, etc...
>
> 2. I'm not aware of any way to change the voltage of a DC circuit. You
> can use a resistor to limit current, but AFAIK there's no way to
> actually change voltages.
>
You're kidding, right?
You can affect voltage by either using a regulator (true, it does this
by altering current) or if you need more voltage than is supplied by the
source you can use a charge pump, which will increase voltage by
alternately charging and discharging a bank of capacitors configured in
a very specific way (lots of caps for that one)
>
> Mmm, interesting. (And ridiculously complicated.) I wonder how much of
> this stuff is to do with electromagnetic radiation? (You don't want EM
> interference stopping your motherboard working, and you don't want the
> board to radiate EM either...)
Filtering probably helps that. But at those timings every little thing
in the design becomes critically important. You can literally have a
parasitic capacitance completely filter out the signal.
--
~Mike
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