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UCC25600: When the output is loaded, the inductor current and operating frequency vary significantly, and the operating frequency is higher than the resonant frequency.

user4891990
Prodigy 40 points
Part Number: UCC25600

Tool/software:

As stated in the title, the inductor current fluctuates significantly at full load output. What is the cause of this?

Can be referenced by the following two figures.

input voltage:405V,output voltage:580V,output power:2400W，topology:full bridge LLC

K=7,Lm=175uH,Lr=25uH,Cr=0.06uF

  • 0
    TI__Guru* 86266 points

    Hello,

    Your inquiry is under review and I will get back with you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

    In your scope plot it looks like the oscillator frequency and load current is changing.  Your voltage loop looks like it is not stable.

    I would recommend checking the voltage loop with a network analyzer to check and reset your phase an gain margin.

    You need more than 45 degrees of phase margin to ensure stability and greater than 3 dB of gain margin.  Once you re-compensate your voltage loop this issue should go away.

    Regards,