Variable Power Supply
Variable Power Supply
(OP)
I need to create a power supply that will provide 18-36VDC from a variable 0-5VDC input. The output load will not exceed 600mA. The supply does not have to be precise or finely filtered.
Any tips?
Any tips?





RE: Variable Power Supply
RE: Variable Power Supply
RE: Variable Power Supply
RE: Variable Power Supply
Do you want more voltage than the input voltage? If so, you need a switcher or converter.
If the supply voltage is more than the voltage you need, this is the easiest. You could use a standard 3 pin regulator (likely with a heat sink) if the input voltage is 30V or less (might go higher, dont know).
RE: Variable Power Supply
Input: 1 to 5 volts, variable.
Output: 18 to 36 volts.
When I mentioned the ~48V power supply, I should have used the word "reference" instead of "source".
I'm thinking that with a constant DC source that's above the output I'm looking for, I can take the power supply's output as the input to a custom control circuit, where a 1 to 5 volt control signal will create a new output of 18 to 36 volts (or thereabouts).
RE: Variable Power Supply
This could be done with a simple op amp (zero and span)fed to the common pin of a three terminal regulator like a 317. Open collector like a LM339 would work best with maybe a 10V zener to keep it away from the high end limit of the device.
RE: Variable Power Supply
The adjustable regulator method should work. I have not attempted this circuit in the past (may Operahouse has) but this involves changing the normal ref voltage of the 317 from 1.25V. Not sure this is ok with the manufactured part. I do know they have resistance limitations on this part of the circuit. In any case, it is definately worth checking out.
http://www.fairchildsemi.com/ds/LM/LM317.pdf
RE: Variable Power Supply
It is impossible to use the usual LM317X and 78XX series because they require input voltages which is greater than the required output voltage (usually 2.5V higher). If you want to produce an output voltage from a 1-5V dc source, you may have two options:
Option 1: Design a circuit which involves the help of an pulse train, usually from a 555 chip.
Option 2: Look for an special integrated circuit (e.g. Maxim http://www.maxim-ic.com ) where you can find chips for such applications.
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Emmanuel A. Gonzalez, E.C.E.
ECE Department
De La Salle University - Manila
RE: Variable Power Supply
RE: Variable Power Supply
For further clarification of my requirements: I will be using a National Instruments DAQ board that has an analog output of 0-5VDC. A board I need to test is a DC/DC converter that takes an input from 19 to 36 volts. To test the thing, I need to provide both the lower and upper rated input voltages, and measure the stability of the output under 50% and 100% loads. This will be in a production test environment, with a LabVIEW GUI driving the DAQ card (again, the source of the controllable 0-5VDC).
I'll dig around the Maxim site, they do have many voltage conditioning devices to choose from.
Thanks for everyone's input, if anybody has any further suggestions, I'd enjoy reading them.
-SC
RE: Variable Power Supply
If going the DAQ route, just a note that output of analog out is limited to about 10ma, I think. Another concern is electrical isolation- What if the UUT is defective, can it take out the DAQ card and the PC? Think production test environment.
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
RE: Variable Power Supply
RE: Variable Power Supply
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Emmanuel A. Gonzalez, E.C.E.
ECE Department
De La Salle University - Manila
RE: Variable Power Supply
SantaCruZin,
It sounds like you only need the low and high voltages, why not two supplies and a digital selection between them? Use foldback supplies so bad product doesn't even blow a fuse.
If you must have the variable voltage there are many PS with analog input control that will provide output current displays, fault current limiting, etc, that your LM137 type solution will not provide without extra effort.
RE: Variable Power Supply
Thanks again, this forum is a great resource!
RE: Variable Power Supply
-Pete
Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.
RE: Variable Power Supply
It also prevents you from being the fireman for the test jig everytime a bad product toasts it. Good call.