Power Supplies

Discussion in 'General Electronics Chat' started by mlkcampion, Jan 3, 2007.

  1. mlkcampion

    Thread Starter Active Member

    Nov 16, 2006
    59
    0
    Is it possible to limit how much a power supply can supply to a load. For example i have a 250w power supply where under normal running the load draws about 150w at 24vDc. However on start up the current draw overshoots and can draw upto the maximum the power supply can give for about 2 minutes. What i'd like to do is limit the power supply to give say 160watts at any time?
    How do i go about this?

    Thanks
    Michael
     
  2. Papabravo

    Expert

    Feb 24, 2006
    9,898
    1,722
    Yes, I believe it is possible. Most lab supplies have both a constant voltage and a constant current setting. The constant current mode allows any amount of current at the voltage setpoint upto and including some maximum. When the maximum current is reached the regulation circuit keeps the current constant and drops the voltage. That's not quite what you asked for; it is not constant power.

    To do a multimode supply with your own circuitry is a bit more complicated, but still doable. You have to make sure the cost of building, what is mass produced in Asia, is worth it to you for some reason.
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    You could use on of these.
    http://www.ametherm.com/Inrush_Current/inrush_current_faq.html

    It's at a very high resistance at first then reduces resistance as it gets warmer. You'd have to check if this would be compatible with your circuit.

    Another variant that would need scaled up to your currnet limit.
    http://www.discovercircuits.com/DJ-Circuits/lampcurrentlimit.htm

    Nice article on inrush limiting with a circuit.
    http://www.edn.com/article/CA244147.html

    More
    http://www.st.com/stonline/products/literature/ta/9115.pdf
     
  4. KrisKizlyk

    New Member

    Jan 6, 2007
    8
    0
    What you can do is create a current supply by using a simple Lm117 or Lm317. Just check out the Data Sheet, it will give you a whole shwack load of current limited circuits for battery chargers. I think the one that your looking for is on page 17 of 26 on that data sheet.

    http://www.national.com/ds/LM/LM117.pdf

    You could always try to design a soft start power supply.

    http://sound.westhost.com/project39.htm
     
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