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Computer controlled power supply

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House91320:
My friend and I are building a computer variable power supply and were wandering if there is a way to input 0-5 and out put 0-30.

scrat:
Can you be a little more clear?
If you mean input voltage < output voltage, there are switching topologies making it possible (under certain limits, of course).

stl:

--- Quote from: House91320 on May 25, 2011, 11:08:10 pm --- My friend and I are building a computer variable power supply and were wandering if there is a way to input 0-5 and out put 0-30.

--- End quote ---

You're making a variable power supply from an ATX power supply? How much current will you need?

You can see here how you can do it:
http://www.wikihow.com/Build-Your-Own-Variable-Bench-Power-Supply-Using-an-ATX-Power-Supply

It's fairly easy to make one variable between 1.3~22V, but up to 30V it's more tricky, I've done one recently that I can adjust between 1.33-33V but didn't tested properly yet with a "heavy" load.

You will read some opinions advising you not to do it and just buy a proper bench power supply, witch I also recommend, but if the cost is a issue there are other solutions. It all depends of what you need it for, how much current you will you need. Using a computer power supply may not be the best solution for you...

House91320:
I should have specified my friend and i would like to make it a liner supply. the control of the supply has to be 5 volts not the vi.

Bored@Work:

--- Quote from: House91320 on May 25, 2011, 11:08:10 pm --- My friend and I are building a computer variable power supply and were wandering if there is a way to input 0-5 and out put 0-30.

--- End quote ---

Let me ask if you are clear on the concept that you can't make 30 V out of 0V? You are aware of the concept that you need to put more power in than you will get out? A 5V 100mA source will not give you more then 17mA at 30 V, in practice you'll be lucky if you get more than 10mA.

As for the rest, yes, there are SMPS topologies where the input voltage can be within the range of the output voltage. E.g. SEPIC, the similar Zeta converter, Cuk converter, or buck-boost.

An SMPS with variable output is tricky, regulating it continuously down to 0V is even more tricky. Using a SMPS as a tracking pre-regulator to a linear regulator, might be an option. The linear regulator then still needs to be specially designed to regulate down to 0 V.