AN2644 datasheet(62/64 Pages) STMICROELECTRONICS

62 / 64 page

Input current in LLC resonant half-bridge with split resonant capacitors

AN2644

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Note that the input current is the same as in a full-bridge converter, where during each half

switching period there is a conducting path drawing current from the input source.

With the same DC value of Iin, then, the split capacitor configuration makes its peak and

squared rms values are cut in half. Unlike bridge converters, however, the currents I(Q1)

and I(Q2) keep the same value as in the single capacitor half-bridge version.

It is then advantageous to use the split capacitor configuration to reduce not only the ac

current requirements on the resonant capacitors but also the ac current in the input

capacitor and the differential-mode conducted noise. It is then easy to find this solution at

higher power levels but it is advisable to use it also when there is no front-end PFC pre-

regulator. In this case, in fact, the differential-mode noise that the input EMI filter is required

to mitigate is that generated by the resonant half-bridge converter (whereas, with a PFC

front-end the noise generated by this stage would be largely dominant), thus it is possible to

maximally benefit from the reduction of its differential-mode component.

AN2644 Datasheet(PDF) 62 Page - STMicroelectronics