On 8/14/06, William Chops Westfield <westfw@mac.com> wrote:
>
> I've always been curious why there aren't offline supplies that
> use a triac-clipper (ie lamp-dimmer) as an input stage.  Wouldn't
> that provide a very cheap step of voltage reduction that would make
> the following stages much easier?
>

I think that this is not necessay. Off-line PWM switching converter has
been cheap and good enough to avoid using those phase controlled
rectifier. Those Triac/SCR phase controlled rectifiers might not
so good to meet EMC requirement and they are not necessarily
cheaper. They are very bad in terms of power factor --> very high
THD (total harmonic distortion).

Regards,
Xiaofan
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