Question about SMPS output current

Discussion in 'The Projects Forum' started by hunterage2000, May 16, 2015.

  1. hunterage2000

    Thread Starter Active Member

    May 2, 2010
    I have built the attached Buck SMPS and put a resistive load on the output to see if it could source close to the max rated output current of 2A.

    The output voltage is 5.45V unloaded but starts to drop with a resistive load of 2k to 5.35V and pulling 27mA for some reason not 2.6mA.

    Looking at the estimates, it says output power is 5V x 2A. So should the voltage hold at 5V up to 2A before it starts to decrease with more than 2A being pulled.
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    have you measured the resistor load, your figures would suggest a 200 ohms load?
  3. hunterage2000

    Thread Starter Active Member

    May 2, 2010
    Yes, measured the load. reads 2k and checked the bands Red, Black, Red, Red. Rechecked the voltage at 5.5V and current is 28mA. I realized I used a 2.2uF electrolytic cap for C6 in the error amplifier so changed that to 20 x 0.1uF ceramic caps in series with hasn't changed anything.
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009

    If you build this on a white board, it will not work as advertized. It has to be on a PCB or at least hand-wired, soldered, using large, short conductors.
  5. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    You are reading the resistor backwards. Red-Red-Black is 220 ohms.