ST AN2708 APPLICATION NOTE

AN2708

Application note

2X36 W digital dimmable ballast with L6574 and ST7FDALI

Introduction

This document describes a high-efficiency, high power factor, low THD and digital dimming electronic ballast designed to drive 2X36 W T8 tube lamps.

The system consists of three main blocks:

The high-frequency ballast includes an active power factor correction circuit based on the L6562 for universal input voltage as well as a ballast control circuit based on the L6574. The digital dimming is performed by interfacing the ST7FDALI microcontroller with the analog half-bridge driver.

The DALI control unit is dedicated to address the slaves, to display the lamp status and to send the dimming commands. This unit is provided with a keyboard which allows setting different dimming scenes over a wide range (5-100%) as well as putting in standby and restarting the ballast. The DALI communication protocol includes single and group mode, as well as broadcast mode to address the slaves.

The AC-DC adapter is based on the VIPer12A-E. This is an offline double-output isolated power supply in DCM flyback configuration. The outputs are set for 20 V to supply the communication bus and for 5 V to supply the MASTER microcontroller.

The three blocks are described in detail and their performances are shown. In addition some of DALI basics are explained.

March 2008

Rev 1

1/42

www.st.com

Contents	AN2708

Contents

1	Block diagram and system operating conditions . . . . . . . . . . . . . . . .		. 5
2	High-frequency ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
	2.1	PFC converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	2.2	Half-bridge inverter and ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14

2.2.1 Lamp dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2.2 Supply section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.3 Lamp turn-on and lamp turn-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.2.4 Verification of lamp status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.5 Ballast performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3	DALI master unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		24
	3.1	Master unit schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . .	26
4	Basics of DALI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		29
5	DALI master AC-DC adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		32
	5.1	Adapter description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	32
	5.2	Adapter bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	35
	5.3	Adapter performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	36

5.3.1 Steady state tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.3.2 Startup behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.3.3 Dynamic load tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.3.4 Line regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.3.5 Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.3.6 Efficiency variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 5.3.7 Conducted emissions test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

6	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	41
7	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	41

2/42

AN2708	List of tables

List of tables

Table 1. System operating conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Table 2. Ballast-slave communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 3. Ballast bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 4. PFC operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Table 5. Power stage design equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Table 6. L6562 biasing circuitry design equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table 7. Lamp parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Table 8. L6574 biasing circuitry design equations for operating conditions . . . . . . . . . . . . . . . . . . . 16 Table 9. Ballast performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 10. Master unit bill of material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Table 11. SMPS operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Table 12. Adapter bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Table 13. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3/42

List of figures	AN2708

List of figures

Figure 1. System block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 2. 2X36 W digital dimmable ballast with L6574 and ST7FDALI . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 3. Ballast schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 4. PFC performances at 230 Vac-50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 5. Lamp ballast model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 6. Ballast transfer functions (magnitude) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 7. DALI protocol brightness values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 8. Ballast controls timing chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 9. Idle state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 10. Turn-on procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 11. Turn-off procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 12. Forward frame timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 13. Backward frame timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 14. Ballast startup at 230 Vac-full power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 15. Lamps turn-on at 230 Vac-full power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 16. Lamps running at 230 Vac - full power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 17. Polling keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 18. Pressed button event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 19. Master unit schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 20. Cable wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 21. Master flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Figure 22. Slave flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 23. Adapter schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 24. Adapter PCB layout - top side -silkscreen (to scale). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 25. Adapter PCB layout - bottom side - copper tracks (to scale) . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 26. Flyback transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 27. VIPer12A-E steady state behavior at full load at 110 Vac - 60 Hz . . . . . . . . . . . . . . . . . . 36 Figure 28. VIPer12A-E steady state behavior at full load at 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . 36 Figure 29. VIPer12A-E steady state behavior at minimum load at 110 Vac - 60 Hz . . . . . . . . . . . . . . 36

Figure 30. VIPer12A-E steady state behavior at minimum load at 230 Vac - 50 Hz . . . . . . . . . . . . . . 36

Figure 31. Startup waveforms at full load at 110 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Figure 32. Startup waveforms at full load at 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Figure 33. Startup waveforms at minimum load at 110 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 34. Startup waveforms at minimum load at 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 35. Dynamic load waveforms at 110 Vac - 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 36. Dynamic load waveforms at 230 Vac - 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Figure 37. Line regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 38. Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Figure 39. Efficiency variations vs. input voltage at full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Figure 40. Conducted emissions at 110 Vac 60 Hz - full load - line 1 peak detector . . . . . . . . . . . . . . 40 Figure 41. Conducted emissions at 110 Vac 60 Hz - full load - line 2 peak detector . . . . . . . . . . . . . 40 Figure 42. Conducted emissions at 230 Vac 50 Hz - full load - line 1 peak detector . . . . . . . . . . . . . . 41 Figure 43. Conducted emissions at 230 Vac 50 Hz - full load - line 2 peak detector . . . . . . . . . . . . . 41

4/42

AN2708	Block diagram and system operating conditions

1 Block diagram and system operating conditions

Figure 1 shows the block diagram of the system.

Figure 1. System block diagram

HIGH
FREQUENCY
BALLAST
ACíDC ADAPTER	MASTER UNIT	SCI
		Communication
		Option

SCI communication is considered as an option.

5/42

Block diagram and system operating conditions	AN2708

The present system has been designed according to the following specifications:

Table 1.	System operating conditions
	Parameter	Value
	Input voltage range	176-265 Vac/50 Hz; 90-140 Vac/60 Hz
	Lamp type	2X36 W T8 tube lamps
	Circuit power (max)	80 W
	Lamp power (max)	72 W
	Dimming range	5% to 100%
	Power factor	> 0.99
	Current THD	< 10%
	Warm start	< 1.5 sec
	Standby mode power	< 0. 6 W

In addition to the previous specs, the DALI communications are optically isolated, the digital dimming is performed with high precision, and the lamp filament preheating time is programmable as well as the ignition time.

Figure 2. 2X36 W digital dimmable ballast with L6574 and ST7FDALI

HIGH FREQUENCY BALLAST

MASTER UNIT

ACíDC

ADAPTER

6/42

J1

FUSE 4A/250V

3	Line
2	Neutral
1

CON3

7/42

	4
	+
1
NTC	-
	2

15E@25° 3A

BRIDGE

W08G

3

D2

4T1

1

STTH1L06

R14

R17

R1

R4

R9

On Air

10E

On Air

22E 1W C11

5

8

750K

180K

750K

1%

1%

C10

1nF

TRANSFORMER

D3

DZ1

4.7nF

Rs= max 5 ohm @100kHz

R6

1N4148

15V

630V

R2

R5

68K

R10

0.5W

C14

8

1

750K

180K

750K

1%

1%

100nF

L2

1.8mH

C19

C5

C7

100nF

8

L1

1

C17

C21

100n

+

C4

R8

4.7uF

1.8mH R30_1

100nF

R30_2

100nF

1000n

12K

50V

12

16

100K

250V

100K

250V

PB2

IC_GND

IC_GND

1W

1W

IC_GND

IC_GND

VS

VBOOT

Q2

C1

10E

2

R26_1

R26_2A

R12

STP8NM50

100nF

R21

U1

2

C3

1

120K

2

15

1

750K

5

330n

RPRE

HVG

R26_2

8

VCC ZCD

COMP

INV

33E

2

+ C6

IC_GND

R15

7

3

750K

180K

1

2

1

10K

SIGN

2

R7

U1

GD

7

1

Q1

47uF

OPIN+

U2

14

R27_1

STP8NM50

400V

3

MULT

L6562

GND

3

L6574

OUT

750K

CS

OPIN-

Q3

2

Lamp1

Lamp2

C9

6

R22

R27_2

C18

C20

R3

C2

STP8NM50

T8 36W

6

4

100nF

11

10E

750K

T8 36W

8.2nF

8.2nF

10K

10nF

1600V

1600V

1%

5

LVG

1

OPOUT

3

4

3

4

D4

8

EN1

3

D5

BAT46

R13

RS1

RS2

R11

1N4148

EN1

D11

R23

47K

0.82E

0.82E

9.53K

1W

1W

1%

R16 68K

4

9

EN2

1N4148

330E

D7

BAT46

RING

CPRE

EN2

CF

GND

R20

R28_2

IC_GND

R18

3

1

10

C15

+

1K

R28_1

R29_1

R29_2

68K

4.7K

4.7K

15K

15K

330uF 25V

RS_1

RS_2

IC_GND

C12

C13

IC_GND

1E

1E

T1: Boost Inductor Spec (ITACOIL E2543/E)

IC_GND

470pF

0.6W

0.6W

- E25x13x7 core, 3C85 f errite

1000nF 25V

IC_GND

- 1.5mm gap f or 0.7mH primary inductance

IC_GND

IC_GND

R24_1

R24_2

- Primary : 105 turns (20 x 0.1mm)

680K

680K

- Secondary : 11 turns (0.1mm)

D14

Rup

Rf

R19 10K

STTH1L06

120K

15K

D8

D6

BAT46

600V 1A

C8

PWM0

1N4148

DZ2

100nF

Rlow

Cf

+

D9

BAT46

4.7K

4.7uF

15V 0.5W

+ CVdd

50V

R25

L4

Cf b

10uF 25V

IC_GND

IC_GND

IC_GND

J2

C16

D10

470E

680uH

4

3

22nF 25V

L3

U7

LE50CZ

1

10nF 25V

BAT46

L1&L2: Choke Inductor

D15

240mA

5

1

1.8mH 95mA

3

1

EN1

2

- E25x13x7 core

D

Vdd

FB

S

GND

VOUT

5VDD

EN2

3

68K

- 2.62mm gap f or 1.8mH inductance

6

D

2

VIN

5VDD

4

R100

D61

1N4007 1A 1000V

7

D

S

5

BAT46

- 267 turns (AWG 40)

8

D

Cout

PB2

6

IC_GND

PB1

SIGN

+

+

+

2

7

D12

+

C42

SIGN

1%

Cin1

Cin2

D13

3.3uF 450V

3.3uF 450V U8

Viper12A

STTH1L06

10uF 25V

18V 0.5W

2.2uF16V

C73

C72

600V

CON7

68pF

33nF

1A

Vss_STDALI IC_GND

50V

50V

Vss_ST7DALI

IC_GND

IC_GND

5VDD

5VDD

J3

1

J4

5VDD

1

LD1

LD2

PWM0

2

RED

GREEN

CON2

1

4 +

D16

- 3

EN1

3

+

HSMS-C670HE

HSMG-C670

2

MB2S

EN2

4

C43

C44

DALI Bus

5VDD

5

1uF

100nF

5VDD

R60

PB2

6

16V

50V

2

SIGN

7

0

IC_GND

IC_GND

5VDD

D17

IC_GND

CON7

R63

R64

U9

BAS16

R61

U10

U11

2K49 2K49

1

1

4

1

4

Reset

1%

1%

4

11K

1

4

IC_GND

1

VSS

OSC1/CLKIN

20

R62

2

19

2

2

3

1%

2

3

5VDD

3

VDD

OSC2

18

3

2

3

4K7

4

RESET

PA0(HS)/LTIC

17

5VDD

SFH6156-2

SFH6156-2

C45

PB1

5

SS/AIN0/PB0

PA1(HS)/ATIC

16

1%

SCK/AIN1/PB1

PA2(HS)/ATPWM0

100nF

6

15

R65

R66

PIN3 SFH6156-2

50V

PB2

7

MISO/AIN2/PB2

PA3(HS)/ATPWM1

14

PWM0

J5

332R

4R7

IC_GND

EN1

8

MOSI/AIN3/PB3

PA4(HS)/ATPWM2

13

10

9

1%

1%

EN2

9

CLKIN/AIN4/PB4PA5(HS)/ATPWM3/ICCDATA

12

Reset

8

+

+

7

10

AIN5/PB5

PA6/MC0/ICCCLK/BREAK

11

6

+

+

5

3

DALIIN/AIN6/PB6

PA7/DALIOUT

+

+

D18

R67

R68

4

3

+

1

Q4

2

+

+

1

C46

BC817-25

BZX284C 2V7

0

R69

R70

ST7FDALIF2M6

+

+

22uF

2

0.5W

1k 1%

1k 1%

ICP Connector

R71

20V

R72

IC_GND 10K

IC_GND

IC_GND

1K21

3K16

1%

1%

1%

PIN3 SFH6156-2

IC_GND

schematic Ballast .3 Figure	the and stage output the circuitry, driving inverter bridge-half the stage, correction .3 Figure in shown is board the of schematic The .unit slave	power the includes which board ballast frequency-high the describes section This
	DALI	factor

2

ballast frequency-High

AN2708

ballast frequency-High

High-frequency ballast	AN2708

This block is essentially a "double board" as the DALI slave board and its external circuitry are mounted on a small separated board which is connected to the bottom side by means of a 7-pin connector. Table 2 shows the ballast-slave communication.

Table 2.	Ballast-slave communication
Pin ref.	Description	Analog stage							Microcontroller
1	PWM0 (ref op-amp)
2	Disable L6574 EN1 & disconnected lamp
3	Enable L6574 EN2 & not ignited lamp
4	GND
5	5 VDD
6	PB2 disable PFC
7	SIGN (lamp failure)

Table 3.	Ballast bill of material
Reference		Value	Description
Bridge		W08G 1.5 A 800 V	Bridge rectifier
Cout, CVdd		10 µF 25 V	Electrolytic cap
C7,Cf		4.7 µF 50 V	Electrolytic cap
Cfb		22 nF 25 V	Ceramic cap
Cin1,Cin2		3.3 µF 450 V	Electrolytic cap
C1		100 nF 400 V	Polyester cap
C2		10 nF 50 V	Ceramic cap
C3		330 nF 50 V	Ceramic cap
C4		1000 nF 50 V	Ceramic cap
C5,C8,C9,C1		100 nF 50 V	Ceramic cap
9
C6		47 µF 450 V	Electrolytic cap
C14		100 nF 100 V	Ceramic cap
C10		4.7 nF 100 V	Ceramic cap
C11		1 nF 630 V	Evox Rifa polypropylene cap Rsmax = 5 Ω at 100 kHz
C12		470 pF 50 V	Ceramic cap
C13		1 µF 50 V	Ceramic cap
C15		330 µF 25 V	Electrolytic cap
C16		10 nF 25 V	Ceramic cap
C17, C21		100 nF 250 V	Polyester cap
C18,C20		8.2 nF 1600 V	Polyester cap
C42		2.2 µF16 V	Electrolytic cap

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AN2708				High-frequency ballast
	Table 3.	Ballast bill of material (continued)
	Reference		Value	Description
	C43		1 µF 20 V	SMD tantalum cap
	C44,C45		100 nF 50 V	0805 SMD cap
	C46		22 µF 20 V	SMD tantalum cap
	C72		33 nF 50 V	0805 SMD cap
	C73		68 pF 50 V	0805 SMD cap
	DZ1,DZ2		15 V 0.5 W	Zener diode
	D2,D13,D14		STTH1L06	STMicroelectronics ultrafast high voltage rectifier 1 A 600
				V
	D3,D4,D8,D1		1N4148	Small signal rectifier 200 mA 100 V
	1
	D5,D6,D7,D9		BAT46 DO 35	STMicroelectronics small signal Schottky diode
	, D10,D61
	D12		18 V 0.5 W	Zener diode
	D15		1N4007 1 A 1000 V	General purpose rectifier
	D16		MB2S 0.5 A 200 V	SMD bridge rectifier
	D17		BAS16	Small signal diode
	D18		BZX284C 2V7	0.5 W Zener diode
	FUSE		4 A 250 V	Radial fuse
	J1		Input 250 V connector	3-way PCB screw terminal, 5.08 mm
	J2		Ballast-slave connector	7-way strip line socket
	J3		Dali Bus	2-way vertical PCB header, 3.81 mm pitch
	J4		Ballast-slave connector	7-way strip line connector
	J5		ICP connector	10-way 2-row vertical through-hole boxed header
	J13			4-way strip line socket
	J14			4-way strip line connector
	Lamp 1		Lamp connector	4-way PCB screw terminal, 5.08 mm
	Lamp 2		Lamp connector	4-way PCB screw terminal, 5.08 mm
	LD1		LS M67K-H2L1-1	2 mA red LED SMD 0805
	LD2		LG M67K-G1J2-24	2 mA green LED SMD 0805
	L1,L2		1.8 mH	Choke inductor 2.62 mm gap, 267 turns (AWG40);
				E25x13x7
	L3		1.8 mH 95 mA	Epcos BC series Axial inductor
	L4		680 µH 240 mA	Epcos LBC series Axial inductor
	NTC		15 Ω at 25 °C 3 A	Inrush current suppressor
	Q1,Q2,Q3		STP8NM50 TO220	STMicroelectronics N-CHANNEL 550 V 0.7 Ω - 8 A
				MDmesh MOSFET

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High-frequency ballast					AN2708
	Table 3.	Ballast bill of material (continued)
	Reference		Value		Description
	Q4		BC817-25		NPN small signal bipolar
	RS_1,RS_2		1 Ω		0.6 W 1% metal film resistor
	RS1,RS2		0.82 Ω		1 W resistor
	R29_1,		15 kΩ		Resistor
	R29_2,Rf
	R28_1,		4.7 kΩ		Resistor
	R28_2,Rlow
	R12,Rup		120 kΩ		Resistor
	R1,R2,R9,
	R10, R26_1,		750 kΩ
	R26_2,				0.6 W 1% resistor
	R27_1,
	R27_2
	R15,R19		10 kΩ		Resistor
	R3		10 kΩ		0.6 W 1% resistor
	R4,R5,		180 kΩ		Resistor
	R26_2A
	R6,R16,R18		68 kΩ		Resistor
	R7		33 Ω		Resistor
	R8		12 kΩ		Resistor
	R11		9.53 kΩ		1% Resistor
	R13		47 kΩ		Resistor
	R14,R21,R22		10 Ω		Resistor
	R17		22 Ω		1 W resistor
	R20		1 kΩ		Resistor
	R23		330 Ω		Resistor
	R25		470 Ω		Resistor
	R60,R68		0 Ω		SMD resistor 0805
	R61		11 kΩ		1% SMD resistor 0805
	R62		4.7 kΩ		1% SMD resistor 0805
	R63,R64		1 kΩ		1% SMD resistor 0805
	R65		330 Ω		1% SMD resistor 0805
	R66		4.7 Ω		1% SMD resistor 0805
	R67		10 kΩ		1% SMD resistor 0805
	R69,R70		1 kΩ		1% SMD resistor 0805
	R71		1.2 kΩ		1% SMD resistor 0805
	R72		3 kΩ		1% SMD resistor 0805

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AN2708				High-frequency ballast
	Table 3.	Ballast bill of material (continued)
	Reference		Value	Description
	R100		68 kΩ	1% SMD resistor 0805
	R24_1,R24_		680 kΩ	Resistor
	2
	R30_1,R30_		100 kΩ	2 W resistor
	2
	T1		Transformer	Choke boost inductor (ITACOIL E2543/E)
	U1		L6562N	STMicroelectronics transition-mode PFC controller
	U2		L6574	STMicroelectronics ballast driver
	U7		LE50CZ TO-92	STMicroelectronics very low drop voltage regulators
	U8		VIPer12A-E DIP8	STMicroelectronics offline SMPS primary IC 730 V 0.4 A
				27R
	U9,U10		SFH6156-2	Optocoupler
				STMicroelectronics
	U11		ST7FDALIF2M6 SO20	8-bit MCU with single voltage Flash memory, data
				EEPROM, ADC, timers, SPI, DALI
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.

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High-frequency ballast	AN2708

The basic design specifications are listed in Table 4.

Table 4.	PFC operating conditions
	Parameter	Value
Mains voltage range: Virms(min) - Virms(max)		90 – 265 Vac
Regulated DC output voltage: Vo		400 Vdc
	Rated output power: Po	75 W
Minimum switching frequency: fsw		35 kHz
Maximum output voltage ripple: ∆Vo		< ± 10 V
Maximum overvoltage admitted: ∆VOVP		60 V
	Expected efficiency: η	> 90 V
	PFC

For reference, it is useful to define also the following quantities:

●Input power: Pi (= Po / η ) ≈ 80 W

●Maximum mains RMS current: Iirms (= Pi/Virms(min)) ≈ 1 A

● Rated output current: Io (= Po/Vo) ≈ 0.2 A

The design guidelines are deeply explained in AN966 ("L6561, enhanced transition mode power factor corrector"), AN1757 ("Switching from the L6561 to the L6562) and AN1089 ("control loop model of L6561-based TM PFC"). The main design formulas are summarized as follows inTable 5.

Table 5.

Power stage design equations

Input capacitor (C1)

Boost inductor

Power MOSFET (Q1)

Boost diode (D1)

C1 = 2π fsw

Irms

Volume ≥ 4K

L

2

VDSS = Vo + ∆ VOVP + Vm argin

r Vinrmsmin-

I

irms

where

Pon = I2Qrms R

r = 0.01 0.1

L =

V2irms

( Vo –

2 Virms)

DS( on)

VRRM = 1.2 Vo

-----------------------------------------------------------------------------2

fsw

Pi

Vo -

where

where

Output capacitor (C6)

K

14

10

–3

Ie

I

=

2 2

Iirms

1

4 2

Virms

IF =

3 Io

Igap------------

Qrms

-- – ----------

----------------

6

9π

Vo

Po

4

I

2

Rcu

Pcu = --

irms

-------------------------------------------------

3

Pcross = Vo

Iirms tfall

fsw

Plosses = VT

IDC + Rd

2

C6 ≥ 4π f

Vo ∆ Vo

I rms

Pcap =

3.3Coss V

1.5

1

2

drain

f

drain + --Cd V

sw

2

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AN2708

High-frequency ballast

Table 6.

L6562 biasing circuitry design equations

Pin 1 (INV)

Pin 2 (COMP)

Pin 3 MULT

Pin 4 (CS)

A RC-C network is

VMULTpkx

2.5

placed between this

2.5

∆OVP = R

40 10–6

Rlow = -------------------------------

–6-=

250-----------------------------10

–6-

1.65

--------------------------------Vinrmsmin

high

pin and pin 1, leading

250

10

Rsense ≤

2

Vinrmsmax

to a low crossover

2

Iinrms

-

(Rhigh + Rlow)

frequency (some tens

Rlow

= 2

2.5

V

= 2.5

of hertz) as well as to

R-------------------------------------low + Rhigh

V

inrmsmax

out

Rlow

an adequate phase

A small capacitor of 10 nF

Pd = Rs

I2Qrms

margin.

filters the signal on MULT pin.

Pin 5 (ZCD)

Pin 6 (GND)

Pin 7 (GD)

Pin 8 Vcc

IC ground. As a layout

Gate driver.

The supply voltage is

(Vout –

2

Vinrmsmax)

provided by a capacitive

m =

hint, this pin has to be

A "bleeder" resistor between

power supply connected to

2.1

1.15

kept separated from

the gate and the source is

the half-bridge inverter.

power ground. All the

used to avoid undesired

R6 ≥

(Vout –

2

Vinrmsmin)

IC signals have to be

switch-on, without affecting

V

inrmsmin

2

----------------------------------------------------------------------

m

3

–3

referred to this pin.

the power consumption.

Rstart =

10

Istartup

The PFC preregulator performances are shown in the following graphs:

Figure 4. PFC performances at 230 Vac-50 Hz

CH1 (yellow): rectified input voltage

CH2 (blue): input current

13/42