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Power Factor Correction

The power factor correction section consists of the Motorola Semiconductor MC34262 Power Factor

Controller IC (IC1), MOSFET M1, inductor L2, diode D2, capacitor C8 and additional biasing, sens-

ing and compensation components (see schematic diagram). The IC was chosen for its minimal

component count, low start-up supply current and robust error amplifier. This is a boost topology

designed to step-up and regulate the output DC bus voltage while drawing sinusoidal current from

the line (low THD) which is “in phase” with the AC input line voltage (HPF). The design of the power

factor correction section was taken from the Motorola Semiconductor MC34262 data sheet and

information on the operation and design considerations for the MC34262 are contained therein.

Ballast Control

The ballast control section is built around the IR21571 Ballast Control IC, IC2 of the Demo board.

The IR21571 contains an oscillator, a high voltage half-bridge gate driver and lamp fault protection

circuitry. A block diagram of the IR21571 IC is shown in figure 1 and a state diagram of the IR21571

is shown in figure 2. Following is a breakdown of the operation of the ballast in all of the different

modes of operation.

OVER-

TEMP

DETECT

LEVEL

SHIFT

PULSE

FILTER &

LATCH

2

4.0V

5.1V

3

5

7.6V

3.0V

5.1V

1

1.0uA

4

2.0V

I

RT

6

I

7

4.0V

2.0V

CPH

RPH

RT

RUN

CT

DT

VDC

Q

S

R2 Q

R1

Q

T

RQ

16

14

15

VS

HO

VB

13

11

12

COM

LO

VCC

15.6V

9

SD

10

0.2V

CS

Q

S

RQ

QD

R

Q

CLK

QS

R

Q

UNDER-

VOLTAGE

DETECT

2.0V

8

OC

50uA

7.6V

7.6V

7.6V

Figure 1: IR21571 Block Diagram