Problem with AC - DC Power Supply

Discussion in 'General Electronics Chat' started by aussa, Apr 17, 2011.

  1. aussa

    Thread Starter Member

    Apr 27, 2009
    Hi, I am currently designing a Power supply with a transformer 220V to 30VAC then using a full bridge rectifier (10A).
    The peak DC voltage (after adding 4700uF with no load) is 30 x 1.414= 42.4V
    I am using two LM338 voltage regulators to step down the voltage to 36Volts.

    The required capacitor to reduce the ripple (Vpp) is around 50,000 uF?? this should tie the Vpp to 1.2 Volts @50Hz, 6Ampere load

    My problem is that I cant find any giant capacitors to reach 50,000uF with rated voltage 50V

    Are there any solutions to that case?

    What would be an acceptable Vpp voltage that wouldn't heat up my regulators and maintain my required regulated voltage?
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
    Dude on eBay has a used set of 5 .01F/50v caps for $137. I found another site that had a new .05F/50 cap for $150.

    How about a capacitance multiplier? Instead of stringing 2 338's together you could use a multiplier and one 338.
  3. aussa

    Thread Starter Member

    Apr 27, 2009
    Thanks JaguarJoe, I found the capacitor multiplier very interesting, I tried a sample circuit on spice and it worked well under 6 amps load, I managed to reduce the ripple to 2 volts. I will build the circuit and check it on the scope and let you know. My concern is: the 2 volts ripple is ok? Or shall I try to reduce it? What is the acceptable Vpp. My circuit is basically a micrcontroller controlling two dc motors.