LM5160: LM5160A CCM mode setting problem

udaykumar vangaveti

Part Number: LM5160

Hi,

I have designed isolated power supply (+15V and -8V outputs) using LM5160A shown below, the primary output at terminal 3 of the transformer is 7.5V. The FPWM pin is connected to Vcc to get CCM mode, but the IC output is always in DCM mode. The transformer inductance value is 10µH. It would be great if someone could help me to solve this problem.

over 5 years ago

0 Arief Hernadi over 5 years ago

TI__Mastermind 23825 points

Hi,

This looks like some kind of instability. Do you use the same value as webench recommend on R50 and C37?

You can also check the ripple injection circuit value here

http://www.ti.com/tool/lm5160dntfbk-calc

You can maybe try to lower the R50 and see if you can inject more current and the circuit will be stable

Thanks

-Arief

0 udaykumar vangaveti over 5 years ago in reply to Arief Hernadi

Prodigy 50 points

Hi Arief,

Thanks for the reply, I will adjust R50 value and will see If the output waveform of the IC stabilizes.

0 Arief Hernadi over 5 years ago in reply to udaykumar vangaveti

TI__Mastermind 23825 points

Hi,

Ok let me know if you still have any issue with the design. For now i will close this thread. Feel free to open it again if you still have an issue

Thanks

-Arief

0 udaykumar vangaveti over 5 years ago in reply to Arief Hernadi

Prodigy 50 points

Hi Arief,

I have adjusted the Ripple circuit now I am getting CCM mode but I have following questions

1. What if I select very low Rr in the ripple circuit (the design file suggest me 140k maximum but I selected 7kOhms resistor and my primary voltage is rising). Does this Rr value effect the secondary currents.

2. In the design calculator how can I select multiple secondary outputs, and I have two outputs (+15V and -8V).

0 Arief Hernadi over 5 years ago in reply to udaykumar vangaveti

TI__Mastermind 23825 points

Hi,

If you have a large Rr value then you will have large injection voltage, in this case you might have a higher output voltage when you have no load.

If you want to check a secondary output, maybe you can try to use this calculator

http://www.ti.com/tool/FLYBUCK-FLYBACK-DESIGN-CALC

Thanks

-Arief

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LM5160: LM5160A CCM mode setting problem