Re: Building computer - power supplies
On 09/29/2013 06:02 AM, Joel Rees wrote:
> On Sun, Sep 29, 2013 at 5:18 AM, Doug <dmcgarrett@optonline.net> wrote:
/snip/
>>
>> Do I understand correctly that there are two switching power supply
>> chips at the input to the CPU to produce 3.3Volts? Obviously, a linera
>> regulator cannot produce and gain in current. Iin = Iout for linear
>> regulators.
>
> I7m confused. Did you mean can't produce a gain in current or power?
>
> --
> Joel Rees
There's a type there. The word "and" should read "any."
A linear regulator can only output as much current as goes in to it--
it functions as a variable resistance witha regulated voltage output.
A switching regulator takes an available amount of _power_, that is,
voltage times current, and converts it into another voltage times
current, of the _same_ power, so you can see that 12V * 1A input
can be translated into 2.4V * 5A = 12W either way. (That assumes
100% efficiency, which is impossible, but is used for illustration.)
So a linear regulator is a lossy device; a switching regulator
_approaches_ lossless translation of power from one voltage to
another.
This discussion assumes DC voltage, of course. For AC, there's
a transformer. Modern power supplies do not use the transformer at the
line frequency, because it would take far too much iron, and be large
and heavy. They rectify the line voltage into DC, and then use a
switching regulator, operating at frequencies in the Kilohertz range,
which does have a transformer, but it is small and light, due to the
frequency of the switched AC voltage. The output of this high frequency
transformer is again rectified to produce the DC needed in the
device it supplies.
For switching regulators that do not require isolation, as the
line-frequency supplies do, the transformer may be replaced by an
inductor.
Hope this clears the air--doug
--
Blessed are the peacemakers..for they shall be shot at from both sides.
--A.M.Greeley
Reply to: