On 9/11/06, Lee McLaren <piclist@lrm.com.au> wrote:
>
> I remember once seeing a circuit for a triac or SCR preregulator for a
> DC power supply but can no longer find the circuit. It was in the form
> of the bridge rectifier and used and error feedback from the output of
> the final regulator so that the final regulator had a pre-set voltage
> drop to keep power dissipation down.


I did that in a printer design, wasn't hard.  Basically, take a "light
dimmer" sort of circuit, and apply the output of a voltage comparator, so
that if your voltage is high enough, you skip the next half-cycle.  Bridge
rectifier on the front end, and SCR between that and the filter cap.
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