AN4213 datasheet(9/42 Pages) STMICROELECTRONICS

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AN4213

Designing a TM PFC

3.1

Input specification

The first consideration for designing a new boost PFC converter is a detailed specification of

the operating conditions of the circuit that is needed for the calculation.

In this example a 116 W, single-input range mains PFC circuit has been considered.

The L6562A integrates an OVP in order to prevent excessive output voltage that can

overstress the output components and the load.

•

Maximum output overvoltage:

The PFC minimum switching frequency is one of the main parameters used to dimension

the boost inductor. The switching frequency at low mains on the top of the sinusoid and at

full load conditions has been considered. It must be higher than the audio bandwidth in

order to avoid audible noise and it must not interfere with the L6562A minimum internal

starter period. On the other hand, if the minimum frequency is set too high, the circuit shows

excessive losses at a higher input voltage. The typical minimum frequency range is 20 - 50

kHz.

•

Minimum switching frequency (kHz):

In order to properly select the power components of the PFC, the maximum operating

ambient temperature around the PFC circuitry must be known. The designer must take into

consideration that it is the temperature at which the PFC components are working and not

the maximum external operating temperature of the entire equipment.

•

Maximum ambient temperature (°C):

Table 1. Specified parameters

Converter specification data and fixed parameters

Symbol

Description

Values

AC(min)

Mains voltage range

185 V

AC(max)

265 V

Minimum mains frequency

47 Hz

OUT

Rated output power

116 W

OUT

Regulated DC output voltage

400 V

OUT

Expected efficiency

90%

Expected power factor

0.99

OVP

kHz

min

ambx

= 50

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