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HiperLCS light load shut down

Posted by: satya123_999 on

Hi,

I am working on 110W (24V4.5A) LLC converter by using HiperLCS.

I am facing an issue at light load condition (<20% of rated load). The LCS IC shutting down due to overheat. The converter is working in burst mode (Approx 360KHz). I had adjusted soft start capacitor but no change.

I have observed, the LCS IC working in burst mode up to 120mA after that it is working normal mode, but i am facing issue( over heat) upto 250mA.

Please suggest any solution

Thanks,
Satya

Comments

Submitted by PI-Mallora on 07/27/2017

Hi Satya,

Thank you for using Power Integrations' part.
Regarding your question, I think your circuit is out of ZVS at light load condition. This will cause heating and eventually hitting the OTP point. To minimize bursting mode, you need to increase deadtime through the DT/BF resistor. What is your Bus Voltage? You can also minimize burst mode by reducing the Bus Voltage input. Those two parameters can reduce your minimum load before bursting or hopefully totally eliminate it. Adding acceptable preload is also an option to totally eliminate burst mode.
Can you share your PIXls design and schematic for my reference? Thank you and hopefully it helps.

I have changed dead time to 350nSec from 320nSec. little bit improved. please check attached design sheet.( I am using E25 core).

I have another issue, during no-load unit starting normally but with load (even 100mA) unit not starting(flickering). I have observed the frequency is above the burst mode limits (operating at Fmax ).

Please reply me

Thanks,
Satya

Attachment Size
ee25 llc - 1.pixls 49.5 KB

Hi Satya,

Can you share your schematic with your values so I can check possible cause of your problem.  If you can also show me the start-up waveforms with atleast output voltage and Vds, it would help me analyze your problem.  Thank you.