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LM5155-Q1: How to Design a Boost Converter Using LM5155

Bruce Link
Prodigy 30 points
Part Number: LM5155-Q1
Other Parts Discussed in Thread: LM5155

For the LM5155 Application Report "SNVA824 ",I need your help.

1.Why maximum ripple ratio occurs at a duty cycle of 33%?if booster output 12V,is this duty cycle “33%” will changed?

2.A maximum ripple ratio is between 30% and 70% ,The following Equation use the ripple ratio is 60%,How do you decide the value to use,why not 30%?

  • 0
    TI__Genius 17175 points

    Hi Bruce,

    1. You can find the result by knowing that ripple ratio means ripple current / inductor current. Maximum ripple ratio occurs at a duty cycle of 33% independent of output voltage.

    2.As described in this section: A maximum ripple ratio between 30% and 70% results in a good balance between the power loss of the inductor, the down slope of the inductor current and the right-half plane zero frequency. It is a tradeoff for the designer to meet the application requirements.

    Best Regards,

    Feng Ji