Low Voltage High Power Supply


2008-01-29 4:27 pm
I am looking to build a decent size DC power supply for a personal test bench for several types of amplifiers(audio and other).

I have seen a design but cannot find it and am hoping some of you guys can help with the design and/or point me in the right direction. The design consist of using SCRs to convert AC/DC.

I have a transformer that will produce and easy 150A at 30V and want to use it in a variable DC supply. The lowest voltage would be 12-13V and highest would be around 28V.

I have done a DC-DC power supply for a vehicle that charged at 12V when activated switched to 24V(reconfiguring the supply configuration of the batteries via relays i.e. 12V lead acid batteries in parallel) this allowed the voltage to be variable from 12V-18V @ X amperage which depended on how many pass transistors were used. This particular one could do 200A using 25-2N3055’s driven by a 2N3055 regulated by a LM317.

I am trying to achieve similar results with out all of the pass transistors and go to 24V. I seem to remember this being done several ways one is using the SCR’s in a full wave form, using the 2 SCR’s on the output of the transformer, and lastly using the scr on the dc side to regulate current flow I believe.

Any help will be appreciated.


2007-03-21 7:42 am
For rectification of big currents scr's are very usefull .
At my work we use scr's for that purpose up to 200 Amperes .
Regulating with the scr's is in itself not that hard ,just think of the principia of the light dimmer .
(the link shows the idea what i mean)
This can be fairly simple done with scr's of which you control the point of triggering with for instance the moc 3021 .
Basicly it boils down to this ,a scr works opened as a diode .
You just have the luxury of control .
For transfomers this big it might be wise to include a softstart in your setup .
(just to limit the inrush current of your transformer)

Good luck .


2008-01-29 4:27 pm
Yes that is what I was thinking.

My problem is coming up with a scr firing board to control the SCR's. Any recomendations or info on building one?

I have seen one work before and it did beautiful but it was a comercial unit and not schematics and a while ago that I saw it.

I know I will need to mat a RC snubber for it and a few other things just not sure on how to get or go about the firing board.
I have a couple of high current Farnell variable lab DC supplies that use the SCR technique as a way of reducing the dissipation in the series regulator. The biggest of these is 0-30 vdc at upto 100 amps !!! It's a superb unit , weighs 90 KG and has more reservoir capacitance than I've ever seen !!!

I have the manuals which include circuit diagrams and descriptions. If thats of interest I could scan and email to you next week ?