current regulator using LM723

Discussion in 'General Electronics Chat' started by jishnup, Dec 28, 2012.

  1. jishnup

    Thread Starter New Member

    Dec 23, 2012
    I need to drive an LED (actually three parallel led arrays each array at 15V,150mA ) at 15V ,1.05A. Also need to adjust the current with maximum precision. Does it possible with LM723 together with series pass transister ?How would be the circuit diagram? (I had seen the LM723 configuration for high voltage regulation and low voltage regulator with current booster. But not confident with a high voltage ,high current configuration.)
    Is there any other better circuit for my requirement?
    Can i use LM723 as voltage regulator and LM317 as a precise current regulator along with it for better accurate controlling of current ?
    HELP me please...........
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    Please read something on Ohms law, you cannot control both voltage and current at the same time.
    I think that a simple LM317 current regulator should be accurate enough. Or what accuracy do you require?
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    LM317 current source info:

    If using an LM317 constant current source you need about 3 volts extra to make up for the CCS voltage drop.
    If your LED modules need 15vdc the 15vdc @1.05 amp supply would not provide the extra voltage needed.

    Do you have options on the LED configuration or the power supply voltage ?
    If the power supply is an un-regulated wall-wort they generally provide more voltage when operated at reduced current
    it may possibly (barely) work.
  4. Audioguru

    New Member

    Dec 20, 2007
    I already answered your questions but the current was higher. Maybe from another kid in your classroom.
    You DO NOT need a voltage regulator because LEDs set their own voltage. Instead you need a current regulator (an LM317 makes a good current regulator if you can find a suitable low ohms pot with a reverse logarithmic taper to adjust the current, or use switched resistors).

    You DO NOT need an ancient LM723 voltage regulator.
    abhaymv likes this.
  5. #12


    Nov 30, 2010
    A 723 will do the job but it's way more horsepower than you need. Nobody with good experience would bother wiring up such a complicated chip to do this simple job.
    abhaymv likes this.
  6. Audioguru

    New Member

    Dec 20, 2007
    Maybe the teacher doesn't know anything about electronics so told the students to use an ancient LM723 voltage regulator instead of using a current regulator?
    I think so.

    In university I had a couple of professors who could barely "speeky zee Engrish" and knew very little about electronics. Me and other students got them OUT OF THERE!
    jishnup likes this.
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    A teacher may now and then create projects that may seem awkward in order to educate the students. Also the LM723 do have a current limiting built in. With some tuning it can be quite accurate
  8. ScottWang


    Aug 23, 2012
    abhaymv likes this.
  9. Audioguru

    New Member

    Dec 20, 2007
    The old LM723 voltage regulator has very simple current limiting (not current regulation). The amount of limited current changes when the voltage changes (like a simple resistor)and when the temperature changes. It is not suitable for powering LEDs.

    An opamp, a power transistor and a current sensing resistor makes a much better current regulator.
    abhaymv likes this.
  10. Audioguru

    New Member

    Dec 20, 2007
    Thank you for your personal message to me.
    The other similar thread WAS from a classmate of yours!
  11. abhaymv


    Aug 6, 2011
    The PM was actually from me:D.
    Unless he PM'ed you too:confused: