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Hi all

Requirement: 5V-5V isoltaed and load regulated power supply, load current-0-500mA

I am getting 5V output at no load, but when load increases output voltage decrease rapidly and at 500 mA load output voltage become 0.235 volt.I tried changing compensation resistor so as to increase gain, but it dint work. Can anyone suggest what should be done to keep the output voltage stable at 5V in 0 to 500mA load.

  • \$\begingroup\$ If you ground pin 2 when you have 500 mA load what happens? ie doing that runs converter at full output IF you do not get >= 5V in that condition then problem is at least partly with ability of converter to supply power. T1 then is suspect assuming IC can handle power level. Link to specs and datasheet for U1 and T1 are needed. \$\endgroup\$
    – Russell McMahon
    Commented Jul 24, 2015 at 6:54
  • \$\begingroup\$ It's very important to exactly follow the dot notation used on the transformer winding - have you done this? \$\endgroup\$
    – Andy aka
    Commented Jul 24, 2015 at 8:52
  • \$\begingroup\$ There's a problem with impedance on the output of the transformer (no feedback from output). There could also be problems with poles created by having the feedback path through a transformer, such as instability or oscillation. Personally, I'd get simpler, with a 555-based PWM controller feeding fluctuating current into the transformer and a linear 5V regulator on the output side. \$\endgroup\$ Commented Sep 19, 2015 at 9:24

1 Answer 1


You must supply the input with about 800ma, then the output will be 500 mA. Your source only has ~24mA available, so you only have 20mA output available. You cannot create power with this part, only move it from one side to the other.


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