Lab Power Supply w/ Op-Amps (CV and CC)

Discussion in 'The Projects Forum' started by TheLaw, Apr 23, 2012.

  1. TheLaw

    Thread Starter Member

    Sep 2, 2010

    I'm sure this is a pretty frequent topic...but here's my spin on it.

    Like a lot of people, I want to develop a power supply for my lab. Eventually I would like it to be a dual supply, but for now I just want to get the theory down for one.

    I would like to be adjustable constant voltage and if too much current is drawn for it to change to adjustable constant current. By adjustable, I mean potentiometers setting the CC point and the CV.

    The voltage regulation part is pretty bog standard. Non-iverting type op amp configuration. The constant current part I guess can be achieved through an op-amp current source.

    My main question is...What can I use to determine whether CC or CV should be enabled? And then how can it switch seemlessly between them. I've been trying to decipher the schematic of Agilent E361x Power Supply for ideas but I've very confused.

    Any ideas?

  2. #12


    Nov 30, 2010
    Study the datasheet for the LM723 chip.
    Seamless crossover is not a problem in that all you have to do is collapse the reference voltage when the voltage on a low side current sense resistor crosses a threshold. This can be done as simply as a 317 chip with a current sense resistor that turns on a single base emitter junction of an npn, and its collector dumps the reference voltage on the 317 feedback loop.

    More sophistocated is to develop a much more adjustable current limit by using an op-amp to compare the voltage across a current sense resistor to an adjustable voltage.

    Gotcha started?
  3. dataman19


    Dec 26, 2009
  4. MrChips


    Oct 2, 2009
    CC or CV doesn't really matter.

    For CV, you monitor the output voltage and feed this back into the inverting input of the op-amp driving the output.

    For CC, you monitor the voltage across a current sense resistor and feed this back into the same inverting input of the op-amp.

    The circuit will automatically switch into CV or CV depending on which threshold is reached first. The switch over is automatic and seamless.
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Here you go.