AN2761 datasheet(28/36 Pages) STMICROELECTRONICS

28 / 36 page

EVL6562A-TM-80W demonstration board

AN2761

28/36

Doc ID 14690 Rev 2

for the reduction of the mains harmonics, which complies with the European norm

EN61000-3-2 or the Japanese norm JEIDA-MITI. This rail is the input for the cascaded

isolated DC-DC converter provides the output rails required by the load. The board has

been designed to allow full-load operation in still air.

The power stage of the PFC is a conventional boost converter, connected to the output of

the rectifier bridge D2. It includes the coil T1, the diode D1 and the capacitor C6. The boost

switch is represented by the power MOSFET Q1. The NTC limits the inrush current at plug-

in. It has been connected on the DC rail, in series to the output electrolytic capacitor, in

order to improve the efficiency during low line operation because the rectifier RMS current is

significantly lower than the AC input current at minimum input voltage and maximum load.

Even in this position the NTC limits the surge current due to the output electrolytic capacitor

as well.

At startup the L6562A is powered by the Vcc capacitor C29 that is charged via the resistors

R4 and R5. Then the T1 secondary winding and the charge pump circuit (R14, C5, D2 and

D8) generate the Vcc voltage powering the L6562A during normal operations. The divider

composed of R1 + R2 and R3 provides the L6562A multiplier with the information of the

instantaneous voltage that is used to modulate the boost current. The divider composed of

R11 + R12 and R13A in parallel with R13B is dedicated to sense the output voltage.

The board is not equipped with an input EMI filter. The filter must be added in the final

application circuit by the user.

AN2761 Datasheet(PDF) 28 Page - STMicroelectronics