LM5160: Secondary output is not stable, It is decreasing drastically with respect to Load current. Switching frequency is also not constant.

Harish acharya Kudure

Prodigy 50 points

Part Number: LM5160

---my circuit---

Input=6V at HV6, Output=5V at P5.0V

my schematic

Why is Output voltage as LM5160 weak and unstable in my circuit?

What modifications are needed to achieve the desired output with good voltage regulation?

Frequency is also unstable

Please give me advise.

Best regard

K. Harish

over 3 years ago

0 Marshall_Beck over 3 years ago

TI__Mastermind 29420 points

Hello Harrish,

Your embedded image isn't showing up in the post.

You are approaching dropout. The switching frequency may be changing to accomadate based on power conditions.

What is loading condition?

What is non iso output voltage?

0 Harish acharya Kudure over 3 years ago in reply to Marshall_Beck

Prodigy 50 points

This is my schematic. Both isolated and non isolated outputs are to be 5V. Loading condition is 5V at 1A load.

0 Marshall_Beck over 3 years ago in reply to Harish acharya Kudure

TI__Mastermind 29420 points

Hello Harrish,

I referenced the LM5160 quick start calc and stipulation is for VIN to be 2x that of VOUT. I believe that to be to ensure appropriate mag current and off time for the device to transfer output power to secondary side.

www.ti.com/.../LM5160

I may need to recommend alternative device for these power conditions.

Do you have any in mind?

0 Harish acharya Kudure over 3 years ago in reply to Marshall_Beck

Prodigy 50 points

Yes I think I have to modify my transformer specs (turns ratio) so to achieve 5V at iso o/p by getting lesser non iso o/p.

Thank you.

0 Denislav Petkov over 3 years ago in reply to Harish acharya Kudure

TI__Mastermind 18940 points

Hello Harish,

You are welcome. Let us know if you need additional help in the future.

Cheers,
Denislav

0 Harish acharya Kudure over 3 years ago in reply to Denislav Petkov

Prodigy 50 points

Actually we have a standard webench design with LM5160 for 6v to 5V flybuck converter. I have tried to simulate the circuit with TINA TI software and on hardware also. I'm not able to get proper simulation results on software and on hardware I'm getting poor voltage regulation on isolated output. I have attached the required files here.7713.5v lm5160.pdf 6507.LM5160 webench TI model.TSCThank you

0 Marshall_Beck over 3 years ago in reply to Harish acharya Kudure

TI__Mastermind 29420 points

Max duty cycle for fylbuck is 50%. 6V to 5V would not be recommended. Forward converter might be an option.

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LM5160: Secondary output is not stable, It is decreasing drastically with respect to Load current. Switching frequency is also not constant.