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Requiring Variable Output Offline Power Supply Info

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barlz

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Hi all,

I'm trying to find information on how to build a variable output offline power supply which will provide an output of 0-20VDC up to 6A. I've found tons of information on constant voltage offline supplies (PC supplies etc) but nowhere can I find info on variable output voltage circuits. If anyone can help or would like to raise questions please do.

Thanks in advance.
 
Hi all,

I'm trying to find information on how to build a variable output offline power supply which will provide an output of 0-20VDC up to 6A. I've found tons of information on constant voltage offline supplies (PC supplies etc) but nowhere can I find info on variable output voltage circuits. If anyone can help or would like to raise questions please do.

Thanks in advance.
A Variac, diode bridge with heat sink and a 24,000 uF capacitor.
 
A Variac, diode bridge with heat sink and a 24,000 uF capacitor.

Thanks for your input but what you are suggesting is far different from what I require for the following reasons:

1) I'm requiring electronic regulation of the output voltage (ultimately I'll be needing a selectable constant volts or constant current regulation.

2) I require better load regulation than what a variac can offer.

3) One thing I should of mentioned earlier is that I need an isolated switch mode supply utilising a flyback transformer etc.
 
i build power supply for that also in canada!! We are manufacturing cathodic protection systems. for that kind of project we use variable dc dc converter with a plc that monitor volatge and current and reference electrodes
 
i build power supply for that also in canada!! We are manufacturing cathodic protection systems. for that kind of project we use variable dc dc converter with a plc that monitor volatge and current and reference electrodes

Hey Carmusic thats cool ! What are the odds of 2 of us on the same thread huh ?

We also offer DC-DC technology as either common positive or common negative configurations but not fully isolated outputs :( Alot of the specification we need to adhere to call for isolated outputs. At present we offer multiple output transformer rectifiers utilising phase angle control which work magnificently but efficiency isn't the best.. ..quite a bit of heat to dissipate.

I cant help but believe that offline switching is the way to go for a new design its just so hard to come across info on variable output circuit variations. All I can find is the typical contstant voltage supplies types.
 
Just incase anyone is interested in this sort of thing. I found a pretty good book to read that actually dedicates several pages on designing a variable isolated flyback power supply - including transformer design. :)
The name of the book is SWITCHMODE POWER SUPPLY HANDBOOK 2nd edition by Keith Billings. Unlike almost all of the designs out there - in this design he discusses the control & PWM circuit is completely isolated from the mains input thanks to the inclusion of a mains driven auxillary supply which the circuit must have anyway.
 
This isn't my field, so can you summarize for us why the voltage needs to be variable?
 
Last edited:
This isn't my field, so can you summarize for us why the voltage needs to be variable?

When it comes to cathodic protection the structure can be in under-protected or over-protected states if too little or too much voltage (or current) is supply to an anode. As time goes on structures will require an increasing amount of voltage (or current) to be supplied to the anode in order to provide a properly protected state - this is often due to deterioration of a protective coating on the structure being protected. Most of the controllers I use have an additional mode of control (auto control) which can vary the output in order to maintain a preset reference electrode potential. In summarizing, when it comes to cathodic protection a variable power supply is a must. And the range of control required can vary from tens of milliamps to several amps on some CP systems. (others can require several hundred amps).
I hope I've helped to answer your question.
 
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