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UCC28710: Troubleshooting Low Output Current

ALI ABDELGHAFOUR
Prodigy 10 points
Part Number: UCC28710

Tool/software:

HELLO

I am trying to build a 12V 5A 60W power supply using the UCC28710. As shown in my schematic, I calculated all component values based on the datasheet recommendations. However, I’m facing an issue: the output voltage is only 10V, and the output current is limited to 0.5A when measured with a multimeter in series with the load.

I experimented by changing the current sense resistor (Rcs) to 0.15Ω, which allowed the current to increase to 1.5A. However, based on the equations from the datasheet, I calculated that for a 5A output, I should be using an Rcs of 0.35Ω.

here is vdd of the ic

V aux before diode

VS PIN 

MOSFT GATE 

  • 0
    TI__Guru* 85676 points

    Hello,

     

    I reviewed your aux winding voltage is being controlled to roughly 20 V through the VS pin at the sample point. 

     

    I reviewed your schematic and R5 and R6 are set to control the output aux winding voltage to 19.75 V.  What this means is most likely your transformer turns ratio is not correct.

     

    The following link will bring you to an excel tool that you can use to calculate the correct turns ratio and magnetizing inductance that you should use for the flyback of your transformer.

    https://www.ti.com/tool/download/SLUC590

     

    Regards,