Problem with LM317 and digital pot

Discussion in 'General Electronics Chat' started by Jan Rune, Apr 27, 2008.

Thread Status:
Not open for further replies.
  1. jvjtech

    Member

    Jan 26, 2008
    23
    0
    I am sorry I cannot offer more than a concept here but I will try. Many microcontrollers have a PWM output and for those that do not one can create a PWM output with an IO pin that is toggled High or Low in the control loop in a controlled fashion, i.e. to adjust the duty cycle. Integrating the PWM output through an RC will give you a voltage relative to the duty cycle. Taking that voltage as a control voltage to the base of a transistor one can vary the current through the transistor. Bring this transistor into the circuit driving the control pin of the LM317 should give you a circuit that has control of the output of the regulator based on the PWM duty cycle. Regards. JJ
     
  2. Wendy

    Moderator

    Mar 24, 2008
    21,838
    3,047
    I doubt the OP will ever see this post. You really need to limit responding to about 3 months or less since the last post. All that has happened here is a very old thread has been dragged up.

    I was guilty too, for what it's worth.
     
  3. megajc1

    New Member

    Jan 29, 2010
    2
    0
    I kind of know what you are trying to do, you are trying to control the voltage trough a darlington transistor, if that is the case you may better use an op-amp, you have already the digital potenciometer just amplify the output voltage with the op-amp, and it is easier to add both ofset and amplifying adjust and it is more lineal than a transistor.
     
  4. megajc1

    New Member

    Jan 29, 2010
    2
    0
    Why dont you use an op-amp to amplify the voltage that comes from the digital potenciometer, in my experience the op-amps are easier to use than transistors, at least for this kind of aplications
     
  5. Wendy

    Moderator

    Mar 24, 2008
    21,838
    3,047
    Check the dates, except for old hands on this site these folks are gone, long gone.

    Welcome to AAC!

    Sit back and chat a while while the soldering iron heats!
     
  6. hp1729

    Well-Known Member

    Nov 23, 2015
    2,304
    284
    I realize this is am old post but for those who might follow ...
    If you want to keep with the same family there is an MCP41HV... that works on resistor voltages outside VDD and VSS.
    If you replace the 220 ohm resistor with a 3K you can use the 50K pot directly.
    As a thought, if you want the power supply to go all the way down to 0 V return the bottom of the pot to -1.2 V.
     
  7. Bordodynov

    Well-Known Member

    May 20, 2015
    2,344
    727
    See

    Stabilizator3.png
     
    hp1729 likes this.
  8. ScottWang

    Moderator

    Aug 23, 2012
    6,762
    1,047
    Please don't reply to the old thread, specially it had 5 years old, because it may bring the alerts to the members who joined the discussion, but the members maybe already leave this site or don't want to get that alert.
     
Loading...
Thread Status:
Not open for further replies.