AN3339 datasheet(18/44 Pages) STMICROELECTRONICS

18 / 44 page

Functional check

AN3339

18/44

Doc ID 18449 Rev 2

Power factor corrector stage

Figure 25 and 26 show some waveforms of the PFC stage under full load operation. THD is

considerably reduced due to the L6564 highly linear multiplier, along with a special

correction circuit that reduces crossover distortion of the mains current. Figure 25 shows

waveforms along a line half-period at 115 Vac. Current shaping is achieved as both CS

signal and peak inductor current are modulated according to the MULT signal, which is

proportional to the input voltage.

Figure 26 represents a detail of the signals in Figure 25; the MOSFET is turned on as the

inductor current reaches zero, obtaining transition mode (TM) operation. As the input

voltage is lower than voltage across inductor, ZVS (zero voltage switching) is achieved.

Figure 27 and 28 show PFC waveforms at full load at 230 Vac. It is possible to observe that

the boost inductor resonance with the total drain capacitance, with an amplitude of twice the

inductor voltage, on the offset of input voltage. Contrary to operation at 115 Vac, the

MOSFET is turned on when there is still voltage on its drain but TM operation assures valley

switching, minimizing switching losses.

Figure 25.

PFC Vds and inductor current at

115 Vac - 60 Hz, full load

Figure 26.

PFC Vds and inductor current at

115 Vac, full load - detail

CH3: CS (pin #4)

CH1: Q1 drain voltage

CH2: MULT (pin #3)

CH4: L1 inductor current

CH3: CS (pin #4)

CH1: Q1 drain voltage

CH2: MULT (pin #3)

CH4: L1 inductor current

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