UC2825: What is switching frequency of UC2825 with RT=6040R and CT = 560pF?

Andrew Massey

Part Number: UC2825

Hi,

I calculate an oscillator frequency of 470kHz with RT=6040R and CT = 560pF with UC2825.

So does this mean that each diagonal pair of the Full Bridge switches at 235kHz?.....and that the switching ripple frequency seen in the output inductor is 470kHz?

over 2 years ago

0 Sean Xu over 2 years ago

TI__Genius 14580 points

Hello,

Did you get the formulator from Datasheet? I didn't see it, can you share it? I can verify it.

Thanks,

0 Andrew Massey over 2 years ago in reply to Sean Xu

Prodigy 120 points

Thanks,

There is no formula.

You have the CT capacitor. This is charged by 3V/RT amps.

It has to charge from 1v to 2.8v......so find the dt for that. as in dt = (C.dv)/i

Then you look at the table to see what dead time the CT value gives.

Then T(sw) = t(charge) + t(deadtime)

...thats how i got it...is this correct?

And supposing it comes to 470kHz.

Does that then mean that each full bridge fet gets switched at 235 khz.?

0 Sean Xu over 2 years ago in reply to Andrew Massey

TI__Genius 14580 points

It is right. Like full bridge, the clock frequency doubles full bridge switching frequency.

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UC2825: What is switching frequency of UC2825 with RT=6040R and CT = 560pF?