AN4077

Main characteristics and circuit description

Doc ID 022997 Rev 1

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Main characteristics and circuit description

SMPS main features are listed below:

This demonstration board implements a power factor correction (PFC) pre-regulator, 100 W

continuous power on a regulated 400 V rail from a wide-range mains voltage and provides

for the reduction of the mains harmonics, allowing the European EN61000-3-2 or the

Japanese JEITA-MITI standard to be met. The regulated output voltage is typically the input

for the cascaded isolated DC-DC converter that provides the output rails required by the

load.

The board is 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 D1. It is completed by the coil L2, the diode D3 and the capacitor C6. The

boost switch is represented by the Power MOSFET Q1. The NTC R1 limits the inrush

current at switch-on. It has been connected on the DC rail, in series to the output electrolytic

capacitor, in order to improve efficiency during low line operation because the RMS current

flowing into the output stage is lower than the current flowing into the input stage at the

same input voltage, therefore efficiency is increased. The board is equipped with an input

EMI filter necessary to filter the commutation noise coming from the boost stage.

voltage startup source, the L2 secondary winding and the charge pump circuit (C7, R4, D4

L2 secondary winding is also connected to the L6564H pin #11 (ZCD) through the resistor

R5. Its purpose is to supply the information that L2 has demagnetized, needed by the

internal logic for triggering a new switching cycle.

The divider R9, R12, R17 and R19 provides, to the L6564H multiplier, the information of the

instantaneous mains voltage that is used to modulate the peak current of the boost.

The resistors R2, R8, R10 with R13 and R14 are dedicated to sensing the output voltage

and feed the L6564H the feedback information necessary to maintain the output voltage

Table 1.

Main characteristics and circuit description

Parameter

Value

Line voltage range

Minimum line frequency (fL)

47Hz

Regulated output voltage

400 V

Rated output power

100 W

Maximum 2fL output voltage ripple

20V pk-pk

Hold-up time

Minimum switching frequency

40kHz

Minimum estimated efficiency

Maximum ambient temperature

50°C

PCB type and size

Single-side, 35 µm, CEM-1, 90x83 mm