L6562A Ver la hoja de datos (PDF) - STMicroelectronics

Número de pieza

componentes Descripción

Fabricante

L6562A

Transition-mode PFC controller

STMicroelectronics 

L6562A

Application information

Figure 19. THD optimization: standard TM PFC controller (left side) and L6562A

(right side)

Input current

Input current

Rectified mains voltage

IInmpauitncsurrent

MOSFET's drainVvdorlatainge

Rectified mains voltage

IInmpauitncsurrent

MOSFET's drainVvdorlatainge

To overcome this issue the circuit embedded in the device forces the PFC pre-regulator to

process more energy near the line voltage zero-crossings as compared to that commanded

by the control loop. This will result in both minimizing the time interval where energy transfer

is lacking and fully discharging the high-frequency filter capacitor after the bridge. The effect

of the circuit is shown in figure 2, where the key waveforms of a standard TM PFC controller

are compared to those of the L6562A.

Essentially, the circuit artificially increases the ON-time of the power switch with a positive

offset added to the output of the multiplier in the proximity of the line voltage zero-crossings.

This offset is reduced as the instantaneous line voltage increases, so that it becomes

negligible as the line voltage moves toward the top of the sinusoid.

To maximally benefit from the THD optimizer circuit, the high-frequency filter capacitor after

the bridge rectifier should be minimized, compatibly with EMI filtering needs. A large

capacitance, in fact, introduces a conduction dead-angle of the AC input current in itself -

even with an ideal energy transfer by the PFC pre-regulator - thus making the action of the

optimizer circuit little effective.

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