From: John Tserkezis 
Reply-To: Fidonet AVtech Echo 

Bob Lawrence wrote:

> JT> Last I heard, every 300W or higher switcher requires power
> JT> factor correction. Nothing wrong with that, they don't have to
> JT> generate as much at the source. 

>  It's crazy, John. SMPS don't take a simewave current, they take a
> short pulse on the peak of the voltage.

  No, they take a short pulse BEFORE and UP TO the peak,  It isn't symmetrical 
around the peak, so it somewhat can be called a capacitive load.

> Power factor correction has no
> meaning unless you filter the pulse with a ballast choke like a
> fluorescent light.

  Kinda, there are "passive" designs around that effectively
shift the pulse 
later, it isn't perfect, but plenty good enough to keep the power authorities 
happy.

> JT> It adds to the complexity, and somewhat adversely affects the
> JT> reliability, but hey, it's all in the interest of better
> JT> overall efficiency. -- 

>  Ask an engineer about it... if you can find one. Hint: the real one
> will laugh.

  I couldn't give a shit.  It's still something I have to fix when it blows up.

>  But it's not funny. At present they get away with it because the big
> users of power are still water heating and motors. If the *main* load
> on a generator ever becomes a short rectified pulse, you can kiss
> goodbye to our power stations...  

  Just repeating what I've heard, though, since then, there are still plenty of 
(current model) 500+W PC power supplies that aren't power factor corrected.

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