WEBENCH® Tools/LM5022: Modified Webench DC-DC circuit not working

Tsvetan Ginin

Part Number: LM5022

Tool/software: WEBENCH® Design Tools

Hi,

I used the WEBENCH tool to generate the appropriate values for my design(LM5022 Flyback), with the exception of the TR1 transformer, expecting compensation problems, but it turned out that the design didn't work at all. At a power supply of 20 volts, the output transistor T1 is driven by IC1 with narrow pulses (80ns / 8V) with a frequency of about 100kHz and heats up strongly. The output voltages are around zero (0.5 and 0.84 volts) without output load. What could be the reason for this? The data of the transformer are plotted in the diagram.

Regards,

Tsvetan

PowerBoard_V2.0_SH1.pdf

over 4 years ago

0 Yinsong Cai1 over 4 years ago

TI__Expert 7450 points

Hi Tsvetan,

Thank you for selecting LM5022. You may need to check the feedback loop. Do you have the waveform of COMP?

Thanks,

Yinsong

0 Tsvetan Ginin over 4 years ago in reply to Yinsong Cai1

Intellectual 470 points

Hi Yinsong,

Unfortunately, the COMP pin has a constant voltage of 5.26 volts, because the optocoupler is not activated at 0.84 volts of the converter output.

Thanks,

Tsvetan

0 Brigitte over 4 years ago in reply to Tsvetan Ginin

TI__Guru 65880 points

Hello Tsvetan,

Sorry for the late response. Would you please share the Webench design as well? What happens if you connect FB to GND?

0 Tsvetan Ginin over 4 years ago in reply to Brigitte

Intellectual 470 points

Hello Brigitte,

I lost some time to find a burned component on the board, but unfortunately it was not the reason it did not work. I shot a timing diagram of the "OUT" and "COMP" pins of the IC and applied them send. I do not see anything abnormal, but the output voltage is double: 25 volt output for 12 volts and 10 outputs 5. Input voltage is 18 volts. The voltage of the "COMP" pin is 1.86 volts.

WEBENCH Link: https://webench.ti.com/power-designer/switching-regulator/customize/37?noparams=0

Thanks,

TsvetanLM5022 signals.zip

0 Brigitte over 4 years ago in reply to Tsvetan Ginin

TI__Guru 65880 points

Hello Tsvetan,

Would you please do me a favor and share your design with me? The link above is not personalized and therefore does not point me to your design. Please open your design in Webench, press on the 3 dots top right in the window and press on the text Share Design. Please share the public link.

Do I understand correct that now your design is switching (at least the signals you are showing look ok), but the output voltage is not at the desired level?

Would you please share your actual schematic?

0 Tsvetan Ginin over 4 years ago in reply to Brigitte

Intellectual 470 points

Hello Brigitte,

That's right, the circuit is correct, but the output voltages are double and the drain voltage rebound reaches 80-100 volts at input 20. In addition, the idle power consumption is high, I do not even dare to run the board without a current limit above 0.5A.

Thanks,

Tsvetan

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=6826F3C501F8DE4D

PowerBoard_V2.1_SCH.pdf

0 Yinsong Cai1 over 4 years ago in reply to Tsvetan Ginin

TI__Expert 7450 points

Hi Tsvetan,

When the output voltage is doubled, what is the voltage at the IC2 reference? It's supposed to be 2.495V.

Thanks,

Yinsong

0 Tsvetan Ginin over 4 years ago in reply to Yinsong Cai1

Intellectual 470 points

Hi Yinsong,

Yes, that's right, I hadn't noticed that the original circuit was for 1.24 volts instead of 2.495. This is where the whole problem came from. Is it correct that the circuit cannot be regulated if the consumption is less than 15-20 mA?

Thanks,

Tsvetan

0 Yinsong Cai1 over 4 years ago in reply to Tsvetan Ginin

TI__Expert 7450 points

Hi Tsvetan,

Yes but remember that you can always add the dummy load to get around this condition.

Please let me know if you have any questions.

Thanks,

Yinsong

Power management

Power management forum

WEBENCH® Tools/LM5022: Modified Webench DC-DC circuit not working