current regulated DC-DC booster

Discussion in 'The Projects Forum' started by anselm, May 1, 2011.

  1. anselm

    Thread Starter New Member

    May 1, 2011
    I just registered.
    I am not specifically electronic trained, but I have some hobbyist notions.

    I am trying to create an adjustable current regulated power supply.
    Input: 3-4V DC (more specifically, a single LiIon cell, 18650)
    Output: 3-7V DC @ a maximum of 1.5~2 Amperes.
    constant current
    , Adjustable via potentiometer or selectable via jumpered resistor, for example.

    At first, breadboard sizes are OK, but if the design is sound, a small PCB version
    would be awesome.

    Can someone "shove" me in the right direction?
    I am still not even sure wether I should make one from scratch using diodes, transistors, caps and an inductor coil, or use one of the many boosting PWM switching ICs.:confused:

    Precise output voltage is not as important as a solid current regulation.

    Any help will be greatly appreciated.
  2. saikat36


    Jan 28, 2009
    I think voltage o/p is manageable but for current no way dude.Simple thing is that one can't go beyond from system i/p power.
    Total o/p power=total i/p power-power loss in system.
    If you somehow manage to get your desired o/p voltage then you have to compromise current. From 1 Li-ion batt. it is hardly possible.
  3. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    My electric RC model airplane was pulling more than 5A from two 18650 Li-Ion cells in series (from a laptop computer battery that had a couple of dead cells) for many flights. But Li-Ion is too heavy for an airplane. My new airplanes use lightweight Li-Po battery cells.
  4. anselm

    Thread Starter New Member

    May 1, 2011
    Yeah, thanks for your comments so far, I know for a fact that 18650s are perfectly
    capable of 2, 3 and even 5 Amps, if the batteries are good and have low internal resistance.

    I'd be happy with an output of 5V @ 1.5A, what I need is a little
    circuit to boost the voltage of the LiIon somewhat while providing a constant current,
    adjustable by the user of up to (ideally) ~2A.

    Has anyone here ever made such a power supply?
    Could it be done with a commercially available IC and some basic
    parts like caps and resistors, or is my requirement so specific that I'd better
    make something from scratch?
    I know there are lots of boost ICs, but most don't handle such high currents, and
    most are constant voltage, not constant current.

    I am not trying to power an RC plane, but a laser diode.;)
  5. anselm

    Thread Starter New Member

    May 1, 2011
    How about this one? MAX1703
    5.5V @ 1.5A output would be fine for me.

    It is not current regulated though, but it has adjustable voltage...
    Couldn't one cleverly trick the circuit into regulating current via regulation of voltage?

    Do I understand it correctly that, for this to work at all, one would still need at least an external inductor coil, besides
    some caps and resistors?
  6. ifixit

    Distinguished Member

    Nov 20, 2008
    Hi anselm,

    Base on your requirements in post #1 you need a design that can both, step-up, or step-down the voltage. A SEPIC power converter (goggle it) can do this.

    Here is a reference to a SEPIC battery charger design that may do the job for your application. It has current limiting that could be made adjustable.

    You may need more than hobby skills to, build, modify and test this design. Call Linear Technology and ask if they sell an evaluation board for this part... and maybe free samples of the part.

    anselm likes this.