Please check my LM317T schematic for errors.

Discussion in 'The Projects Forum' started by tracecom, Jan 12, 2012.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Attached is a schematic for an adjustable regulator using an LM317T. I would be grateful for comments and corrections before I lay out the PCB.

  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    I don't see anything wrong.
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    how you design or it's layout might be the one u must be concerned abt
  4. SgtWookie


    Jul 17, 2007
    My concern is there is no specifications given for desired performance.

    It looks like you are expecting to get about 1.2v to ~22v out, but you didn't mention at what currents.

    Keep in mind that this will work OK for moderate currents at 15v-22v, but you will have too much heat to get rid of in the regulator at low voltage out.
  5. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    Thanks Sgt. Get well soon.
  6. Wendy


    Mar 24, 2008
    I would get rid of D6 and C3, you want the fastest response you can get out of this chip, and they would only slow things down regulation wise.

    If C4 is an electrolytic (which is what is shown) it needs replaced with a non-electrolytic, this is because it is there to suppress possible oscillations. It is basically very similar in function to the sticky Decoupling or Bypass Capacitors, Why? You need a cap that can high frequency transients, which electrolytics can't.

    C1 may be a bit small. I say may because without knowing the upper current limits it is impossible to tell. It fills in the gaps caused by the pulsating DC created by the diode bridge. The more current drawn from this circuit, the deeper the valley between the DC pulses. As long as these pulses are greater than the LM317 set point, the LM317 regulator will compensate.

    Hope it helps.

    20 years ago Radio Shack sold a PCB for the LM317. I used it and made a power supply that is virtually identical to yours. I did include a simple analog voltmeter, with a switch to add a X2 measured voltage function. If I were to do it again I would also add a ammeter.

    Basic Bench Top Power Supplies

    Power supplies are one of the few projects that are practical to DIY for a hobbiest. If you take good pictures you could even post it in the completed projects forum. Pictures aren't that necessary, but they are nice.
    Last edited: Jan 14, 2012
    tracecom likes this.
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I don't know what it does to response time, but this circuit is recommended by TI/National. See fig. 3 in the datasheet.