digital power supply

Discussion in 'The Projects Forum' started by onlyvinod56, Sep 8, 2010.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    hello all,

    I want to design a digital power supply....(I dont know whether the name suits my circuit)
    Here is my idea

    A power supply which can give a wide range of voltage 0-30v.
    The required output voltage can be selected with a button switch.
    If the button is keep on pressed, the output voltage should go 1v 2v 3v 4v ....
    if the button is pressed once, the voltage should go from 0v to 1v. again if pressed 1v to 2v. so, i need two modes. continuous pressing and single step pressing.
    one more button switch required to do the reverse operation.


    what my idea is....
    a button switch - 555(mono) - 4017(10 outputs) - 4066 (analog switches which connects different resistors to adj of LM317)


    Is it clear? or shall i put an attachment. it takes some time to draw in paint.
     
  2. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
    362
    1
    see the attachment
     
    • ps.jpg
      ps.jpg
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It might work. I would want to experiment with the 4066 first. It's hard to get fixed resistors to give the exact voltage desired, too, so incorporating some trimmers for a fine adjustment might help. If you can generate a -1.25 volts reference in place of ground to the regulator, it's also possible to have the 317 output 0 volts.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    I agree.

    A -1.25v ref would give you a 0v.

    I have heard of digitally controlled variable resistors, but have never used them.
    http://www.intersil.com/dcps-dccs/

    That will allow you to use a simple microcontroller to handle the button pressing, voltage display, and the digital-resistor adjustment for the LM317.

    That should help make things a little neater than a bunch of discrete resistors and trimmers.
     
  5. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    Isnt there a passive resistor circuit that somwhat mitigates the diferences in resistor values and allows, by gronding or opening legs, the overall resistance to be varied.

    I cant remember what its called..
    '2:2 ladder' or '2:1 ladder' something like that.

    Anyone have any idea what I am talking about --- clerarly I dont :)

    Al
     
  6. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    Found It .....
    Its called an R-2R Ladder Network :-
    http://en.wikipedia.org/wiki/Resistor_ladder

    I think you may find this useful
    If nothing else it means you could buy just one value of tight tolerance resistors which would probably be cheaper / easer

    Hope it helps
    Al
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Tek used a switching scheme that used values in the order - 1, 2, 2, 5. You can make up all your values from 1 - 9 with fewer values of resistor.
     
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