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5513 Views 3 Replies Latest reply: Sep 1, 2014 9:09 PM by JohnDavis
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# Power Supply with Constant Voltage and Current

I have a friend who is a new hobbyist and had a question about power supply he is looking for that I'm not quite sure about as well. He is looking for a power supply that is able to provide 12V with varying Current from 1A to 20A. He also said that the current must remain constant at a certain level, ie. if at 12V 5A, it should remain 5A regardless of load, and this should be the case for all settings for current. The question I have is, is this even possible?

From what I know, you can regulate either voltage or current, but not both. Ofcourse I'm no expert, so if there is anything remotely close to what he is looking for, do let me know. Thanks!

• 6 posts since
Jul 19, 2011
Currently Being Moderated
Aug 13, 2014 8:51 PM (in response to Riley)
Power Supply with Constant Voltage and Current

Well in a CC/CV power supply one of the paramters is set as a compliance.

So, a CC power supply with a compliance of 100V will provide up to 100V to make the constant current.

With a CV poweer supply, the current is set as a compliance.  e.g, Do not supply more than 10 Amps.

CC is not the same as current limit.  With current limit, you usually lack current regulation.

What he may not know about is an "electronic load".  This device can operate at constant current, constant voltage, constant resistance and constant power.

Another aspect of power supplies is the qudrants of operation.  Most supplies can source a voltage and source or sink a current.

4 quadrant power suppplies or amplifiers can source say a positive voltage and a negative current, so they operate in all 4 quadrants.  V-I+,V-I-, V+I- and V-I+.

Most supplies operate in the first two.  An electronic load operates in all 4.

• 1 posts since
Aug 28, 2014
Currently Being Moderated
Aug 28, 2014 10:43 PM (in response to Riley)
Re: Power Supply with Constant Voltage and Current

If you have a constant current then you cannot hold a constant voltage with variations in the load, If, for example, the current is 5A and 12V then the load is V/I=12/5 (2.4) Ohms. If the load changes to 3 Ohms then the voltage must change to R*I=3*5 (15V).

What your friend proposes will not work.

• 202 posts since
Apr 4, 2014
Currently Being Moderated
Sep 1, 2014 9:09 PM (in response to Riley)
Power Supply with Constant Voltage and Current

simply put, you cannot have both things constant because they affect each other based on the load resistance. As one changes, the other changes as well, you can only keep one of them constant, while the others in a certain range.

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