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TL103W: TL103W operation review request

Grady Lee
Genius 3255 points
Part Number: TL103W

Hi, TI expert.

The client company is testing the LLC block by applying TL103WAIDR.

Spec is shown in the table below.

However, although the output specification is 250Vdc~361.5Vdc and it is fixed at 3A, the phenomenon that the current varies depending on the load during actual operation occurs.

During the test, 250Vdc → 3.7A is output and 360Vdc → 2.6A is output, resulting in an error of about 1A.

I wonder why this is happening.

Below is the current circuit diagram.

Q1) What part of the circuit went wrong?
Q2) Are there any parts to be modified or reviewed?

[Schematic]_Charger_LLC.pdf

Please confirm.
Thank you.

  • 0
    TI__Guru*** 147696 points

    Hello Grady,

    First try removing C354 (lower right side of schematic).  This node is the voltage divider tap between VREF and Current sense voltage that is the input for the op amp. If that is not sufficient, check TL103 pin 7 to see if it is limiting the current (going lower) and check for oscillation (instability).

  • 0 in reply to Ron Michallick
    Prodigy 60 points

    Hello Ron,

    Firstly, I tried the method you said, but the current is not controlled.

    Secondly, when I measured TL103 pin 7, the PWM waveform was observed, and the duty width increased as the load (increased output voltage) increased.

    Q1)  Should the duty of the TL103 pin 7 PWM signal be constant in order for the output current to be fixed when the load changes?

    Q2)  If Q1) is correct, how do I modify the circuit to fix the PWM signal?

    For input/output specifications and circuit diagram, please refer to the file attached by Grady.

    Please confirm.


    Thank you.

  • +1 in reply to Eunseok Kang
    TI__Guru*** 147696 points

    Eunseok,

    The output should be constant when in current limiting for an accurate current limit based on the PWM Duty Cycle and resistors chosen.
    What is the peak to peak voltage on C355?  If a DC voltage was applied to C355, does that solve the problem? If yes, then the C355 ripple should be reduced. What is the frequency of the PWM? Higher would be helpful. Increasing C355 and or all R, 372-376 will help.