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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