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Questions about TPS92310 design fomula

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Genius 4220 points
Other Parts Discussed in Thread: TPS92310

Hi,

I'd like ask about the defference of formulae between TPS92310 Datasheet and App note(SLVA511) as follows,

1. the formula for calculating Lp value on Datasheet P12 is using 85V for VAC_RMS(MIN), 

  but  the formula (11) on App note P12, Vin_min represents 1.3 times of Vac_min.

  These two formulae are same, but the Vin_min values are different.

  Which is correct ?

2. Compared with the formula (9) on App note P12 (IP=2*Iav/（DMAX)) and formula (1)

 (Io=Ip-pk*N*Toff/(2*(Ton+Toff+2*Tdly) on App note P4 ,

 I think that Io and Iav are same, and Toff/(Ton+Toff+2Tdly) replesents (1-Duty),

 So, they become N*(1-Duty)=D.  Is it correct?

and I'd also like to ask about TPS92310 calculator rev1.3,

How to calculate the Recommended turn Ration N (AUX:SEC)

and how to decide the actual turn Ration N (AUX:SEC)?

Now costomer is designing the LED driver circuit with TPS92310 as following conditions,

Vin_RMS 110VAC or 230VAC

ILED=0.29A

VF_LED=3.6V

No. of LED =10

Does someone have calculator or Reference Design with using TPS92310 for those conditions? 

Thanks

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  • 0
    TI__Prodigy 10 points

    Your two questions:

    1. the min Vin is represented as 1.414*Vac_min, pls see ton formula on page 12 of datasheet, this value is only the DC peak of min Vac, for a single stage application with PFC funtion, the max ton time is at the top point of ripple voltage in min Vac, but APP note is for GU10 design with large bulk capactior, because DC Vin has a large ripple valtage, so max ton time must be in the valley of ripple voltage. 1.3 times of Vac_min on App note is a simple and approximate formula which calclulates lowest DC voltage, so two formulas are for two different applications,  you can also find precise formula from other information to calculate the valley voltage of DC input for GU10 design.

    2. Ip=2*Iav/Dmax, represents primary average input current, but formula (1) is output average current Io, so they are not same.

    for single stage application, you can use excel form to calculate  transformer turn ratio. pls send me email, i'll send you this excel form.

    my email: david-dou@ti.com