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LM5026: Load issue for LM5026

Songzhen Guo
Intellectual 2840 points
Part Number: LM5026

Hi expert,

Now LM5026 was used on customer side. Now there is a issue when the load increase to 1W. Could you check it and give some suggestions? Thanks.

Vin: 400V (VDCBUS is the net name in the schematic)   ;  Vout: 24V; 

Issue description:

When there is no load on Vout, LM5026 can work well;

When we add a load on Vout, Iout = 0.05A, Vout drop to 0V;

When change the output to 17.V, Iout = 0.06A, Vout can work well.

 

Here is the schematic for this application. If you have any other question, please let me know. Thanks.

DC-DC -400V-24V Schematic.pdf

 

Best Regards

Songzhen Guo

  • 0
    TI__Mastermind 32775 points

    Hi Songzhen

    Please check COMP, CS at the LM5026. Also, please take measurements starting from the secondary +OUT and working your way through all the control components. Voltage at C38 is the reference - is the reference voltage what you expect? U4A is already set up as type  compensator which should be good for CMC stability in this converter. What is the purpose of C31, C30, R35 and R0615? I would start by removing all the circuitry from the COMP and just put the minimum required which is R37+R39 and R36 (C31 shorted, remove R35, R0615) to set the current gain and make sure the opto is biased correctly so that you see the voltage at U3-3 varying.

    Regards,

    Steve M