In-Rush Current for power supply

Discussion in 'The Projects Forum' started by chimera, Mar 17, 2012.

  1. chimera

    Thread Starter Member

    Oct 21, 2010
    hello! Recently I decided to build a power supply. The one I have right now is big and really just gives fixed out put voltages.

    Sure, I can add an LM317s or LT3080 to give me the variable voltages, but the output range is limited and then there is matter of the heat just a heap of mess to deal with if I want to modify my current power supply.

    I have read up sufficiently on power supplies

    I have a transformer with 50VA @ 24V secondary. I am using the 1n5408 diodes for the rectification (full wave) and 30,000uF filter caps. The output power of my intended power supply is 40W (20V @ 2A).
    There are more elements present but for the sake of simplicity, I haven't included them here.

    So this is what i need help with:

    1- How do I calcuate the inrush current?

    2- Do I really need to be worried of inrush current for a 40W power supply?

    3- What are my options of implementing a in rush currrent limiting circuit---i.e soft start or an NTC thermistor.

    Any suggestions?
  2. chimera

    Thread Starter Member

    Oct 21, 2010
    wow...guys really? no one to help me out??..
  3. wayneh


    Sep 9, 2010
    Usually NO. Your average wall wart works fine without concern about start-up. You haven't said whether your supply is SMPS or traditional transformer.