AN2708 datasheet(11/42 Pages) STMICROELECTRONICS

11 / 42 page

AN2708

High-frequency ballast

11/42

Note:

Resistors are 0.25 W unless specified. Q1, Q2 &Q3 are mounted with 8 °C/W heatsink.

2.1

PFC converter

This block allows drawing a quasi-sinusoidal current from the mains, in phase with the line

voltage in order to get a PF very close to 1 (more than 0.99).

To achieve such high PF the boost topology is implemented because of the advantages it

offers:

●

Minimum number of external components, thus making it a low-cost solution

●

Low input di/dt thus minimizing the noise generated at the input and, therefore, the

requirements on the input EMI filter

●

The switch is source-grounded, therefore is easy to drive

However, boost topology requires the DC output voltage (400 Vdc) to be higher than the

maximum expected line peak voltage.

ST's L6562 has been used as the driver. It implements a transition mode control (fixed ON

time, variable frequency), that, for such output power, is preferred to the fixed frequency

average current mode being simpler and cheaper. The circuit operates on the boundary

between continuous and discontinuous current mode.

Besides providing good results in terms of power factor, this IC considerably reduces the

Total Harmonic Distortion (THD) as it reduces the conduction dead-angle that occurs to the

AC input current near the zero-crossings of the line voltage.

R100

68 k

Ω

1% SMD resistor 0805

R24_1,R24_

680 k

Ω

Resistor

R30_1,R30_

100 k

Ω

2 W resistor

Transformer

Choke boost inductor (ITACOIL E2543/E)

L6562N

STMicroelectronics transition-mode PFC controller

L6574

STMicroelectronics ballast driver

LE50CZ TO-92

STMicroelectronics very low drop voltage regulators

VIPer12A-E DIP8

STMicroelectronics offline SMPS primary IC 730 V 0.4 A

27R

U9,U10

SFH6156-2

Optocoupler

U11

ST7FDALIF2M6 SO20

STMicroelectronics

8-bit MCU with single voltage Flash memory, data

EEPROM, ADC, timers, SPI, DALI

Table 3.

Ballast bill of material (continued)

Reference

Value

Description

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