The one I remember had 2 diodes and 2 scr's in the bridge rectifier,
very simple circuit, probably not a very regulated output but suitable
to feed into a series regulator to lower dissipation.

I will try to track down some of the articles  mentioned, I may have
some of the magazines mentioned.

The output from the final reg will be 80v 20-30 amps momentarily  and
15-20 amp average.


regards

Lee McLaren




Vasile Surducan wrote:
> On 9/11/06, David VanHorn <dvanhorn@microbrix.com> wrote:
>   
>> 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.
>>     
>
> Maybe the SCR in front of the bridge on the AC path, or two thyristors
> as half bridge and two diodes as other half bridge. Else how you fired
> off the SCR as long there is no zero cross (or lower than sustaining
> current of the SCR) current on the filter capacitor ?
>
> Vasile
>   
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