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UCC28180: Vin is 230Vac/50Hz, Vout is set to 408V/850W, Vout has jitter

Part Number: UCC28180

Dear Expert

Vin is 230Vac/50Hz, Vout is set to 408V/850W, Vout has jitter: 380V to 430V,Pin6(Vsense):4.46V to 5.4V. When Pin6(Vsense) rises to 5.0V, the duty cycle slowly decreases, and the Gate will close when Pin6(Vsense) rises to 5.4V. When Pin6(Vsense) drops to 5V, Gate starts to drive, duty cycle slowly increases, Pin6(Vsense) slowly drops to about 4.4V, and Vout also drops. (The above is the 230Vac/50Hz on-load (850W) startup or directly with 850W after startup)

When the input Vin is reduced to 180, this phenomenon does not appear, or when the 230Vac input frequency is changed from 50Hz to 60Hz, this phenomenon does not appear. Or Vout with half load 400W and then cut full load, this phenomenon will not appear.

Abnormal Vcomp waveform for 230V/50Hz input:

Normal Vcomp waveform for 230V/60Hz input:

This is Sch.

  • Hi Gabriel,

    Thank you for the query on UCC28180.

    I went over the schematic and require the following clarifications as they were not shown in the schematic:

    1. The boost inductor value.

    2. Input bulk capacitance.

    3. There is a 450uF cap. shown in the output but the top portion is cut. Can you confirm the total output capacitance?

    4. The upper resistor of the resistive divider which connects to Vsense.

    5. There is a 10nF C10 capacitor connected to Vsense. Can you please reduce this to 820pf?

    7. The full input voltage range?

    There are two level OVP of UCC28180. The OVP_L threshold is 5.35V, if OVP_L is triggered, VCOMP will be discharge to limit Duty. The OVP_H threshold is 5.45V, if OVP_H is triggered, PWM will shundown immidiately. Please share the above information so that I can check the compensation network further.



  • Dear Harish

    1. Inductance: 580uH±20%

    2. 1.55 uF capacitance

    3. Output capacitance: 680uF±20%

    4. Complete line parameters are provided, Q2 is the on-transfer state;

    5. Can be reduced, but no effect;


  • Hi Gabriel,

    Thanks for sharing the inputs. 

    I see that their compensation for the current and voltage loop are off from the recommended calculator values. Please refer the attached excel calculator for the values to be updated in the schematic. The current sense resistor also could be reduced slightly as the ICOMP voltage is close to 5.7V and can cause amplifier to operate in the non linear range. Please let us know your observations after running the tests.