Constant DC current driver from AC?

Discussion in 'The Projects Forum' started by tguarriello, Oct 10, 2006.

  1. tguarriello

    Thread Starter New Member

    Oct 10, 2006
    2
    0
    I'd like to build a driver circuit that, as simply and economically as possible, takes 120VAC input and drives a variable DC load at a relatively constant .85 to 1.0 Amps peak. The output voltage would have to vary from 20 to 90 volts to deal the load changes and maintain the ~1 amp current flow. Ripple and a little noise is not a problem. Load is resistive (not inductive) and changes very slowly. I'm picturing a basic bridge-capacitor supply feeding a power MOSFET or IGBT circuit that is biased using a shunt (sensing?) resistor. I'm an industrial electrician and haven't done this kinda thing in about 15 years. I was hoping to find some example schematics that might help, but I'm coming up empty handed after about 2 hours of googling. Can anyone help?
     
  2. Chris Wright

    Well-Known Member

    Jul 26, 2006
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  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I don't think an LM317 would be up to the task, since max Vi is only 40v.

    MOSFETs and IGBTs are swithces - can't really bias them the way we can with BJTs.

    Might look into a power BJT, something like the MJL1302A.

    Good refresher material can be found here: http://www.national.com/appinfo/power/files/f4.pdf
     
  4. tguarriello

    Thread Starter New Member

    Oct 10, 2006
    2
    0
    Got it! Thanks guys. Good information - After reading through some of this stuff and pulling my old TopSpice program out of the closet (on 5-1/2" disks, so you know how long it's been). I've got a working circuit using a BJT (on paper, anyway).
     
  5. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Ahemmm... Linear audio amplifiers with MOSFET output stages is a myth then ? ;)
    And MOSFET (resistive) dimmers can't be done... Hmmm, one of us needs to read up on the subject I'm afraid :)
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    As I have often said, the universe is full of things I've not heard of.

    That's what makes it such a fun place to live in!;)
     
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