Re: seeking apple IIc brick at 220V

["Luke Forat" <iceman@nospam.digidude.homeip.net>]

    Robert,

    there are several links on the net - here are a few:

    http://computer.howstuffworks.com/power-supply1.htm  (very basic, gives
you some concepts)
    http://www.rdrop.com/~cary/html/switching_power.html (contains several
links to more in depth analysis)

    In brief, the switching PSU used in a PC or electronics device is an AC
to DC converter. It is called so because the input is actually rectified
into DC straight away via a full bridge diode, then, via PWM control logic
is fed to a small transformer through transistors/FETs which work at high
frequency (1KHz or more) and this enables it to be very small and light.
There are 2 (or more depending on power) FETs or transistors that feed the
primary of this transformer switching the input on and off, reversing the
polarity thus creating (integrating) a sine wave in the transformer's
nucleus. This is the main reason they are called "switching" PSUs - because
the input is switched based on the output load on and off with a variable
duty cycle (PWM): the more power is needed on the output, the more the duty
cycle is extended until before saturation of nucleus and power (Amp) limits.
On the output of the transformer you have your AC voltages, depending on how
many secondaries you have (usually +5, +12, -12, -5 for logic and general
use) and this output is fed through high power diodes (especially for +5V
usually 30Amps at least) then through "chokes" or inductances to filter out
switching noise and then across ripple filter caps to the output. Some
designs use full bridge diodes, others only a single or couple of high power
diodes on the outputs. All this works thanks to a feedback circuit, which
monitors the output voltage (usually a single voltage, the +5V which must be
as stable as possible) and corrects the input duty cycle to keep it stable.
This means that the other voltages depend directly on the +5V in PC power
supplies.
    There are other designs using similar techniques (flyback for ex.) but
this goes beyond the brief synthesis of this post.

    Regards,

                Luke

"Robert C." <robc638killspam@sympatico.ca> ha scritto nel messaggio
news:zxFmf.10521$kt5.980875@news20.bellglobal.com...
> "Linards Ticmanis" <ticmanis@gmx.de> wrote in message
> news:439b0ce4$0$27884$9b4e6d93@newsread4.arcor-online.net...
>> Robert C. wrote:
>>
>>> I think Earth is right, if I am not mistaken it is only North America
>>> that uses 110/120 Volts, Every one else uses 220 Volt Mains.
>>
>> Some parts of Asia and South and Central America have 110 Volts too I
>> believe. Japan has 100 Volts I believe. Europe is now on 230V, as a
>> compromise between the old British 240V and the continental 220V.
>>
>> -- 
>> Linards Ticmanis
>
> Just another way of confusing everyone, especially those who must design
> international power supplies. I've often wondered how it's done; I only
> know how to build simple "transformer-rectifier-regulator" type supples.
> Switching supplies like those used on the Apple or PC's are beyond my
> knowledge. (But if anyone knows of a good website that explains switching
> supplies, I'd be willing to learn.)
>
> ~Robert.
>