LM5085: I have prepared one schematic with LM5085 for converting 42Vdc to 24Vdc@3 Amps. Please help me to understand whether I have missed anything or any component has to be modified.

Arkaprava ,

You could have used single stage flyback for this application . The two stage solution is both bulky and inefficient .
www.ti.com/.../PMP10416

Nevertheless below is my recommendations on LM5085 based design .

1. Use Electrolytic cap with ESR in parallel with C8 to dampen out the input filter L2 .
2. Increase the output inductor to 82uH from 22uH .
3. Add another 33uH /50V output capacitor .

--_Ambreesh

Hi Ambreesh,

Thanks for providing feedback.

I have one doubt. As per my calculation (referring Lm5085 datasheet) the L1 value is coming as 22uH. Can you please tell me for what reason you are suggesting 82uH. Because with 22uH I am getting proper output.

One more thing is after simulating in TINA, the starting input current is coming as 14.59A.

I have attached the simulation graph( take a look at AM1 value in legend, this is coming for initial stage). Will it be a major concern in my design?

Thanks&Regards,

Arkaprava Sinha

Arkaprava ,

The inductor should be chosen such that the ripple current though inductor is limited to 20-30% of the Vout . Based on your Schematic the device is switchign at 175KHz and the outptu inductor needs to be increased .

Further you can still see the AC voltage variation at the input of the device . My recommendation here will be to add a bulk cap in parallel with C7 .

--Ambreesh

Hi Ambreesh,

Actually I have made the schematic after considering switching frequency as 500 kHz. after considering formulas mentioned in the LM5085 datasheet, I derived at 22uH inductance value.
Please tell me if I am going in wrong way.

Thanks&Regards,
Arkaprava