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 V

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 V
Figure 15. Lamps turn-on at 230 V
Figure 16. Lamps running at 230 V

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 V
Figure 28. VIPer12A-E steady state behavior at full load at 230 V
Figure 29. VIPer12A-E steady state behavior at minimum load at 110 V
Figure 30. VIPer12A-E steady state behavior at minimum load at 230 V
Figure 31. Startup waveforms at full load at 110 V
Figure 32. Startup waveforms at full load at 230 V
Figure 33. Startup waveforms at minimum load at 110 V
Figure 34. Startup waveforms at minimum load at 230 V
Figure 35. Dynamic load waveforms at 110 V
Figure 36. Dynamic load waveforms at 230 V

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 V
Figure 41. Conducted emissions at 110 V
Figure 42. Conducted emissions at 230 V
Figure 43. Conducted emissions at 230 V

-50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

ac

-full power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

ac

-full power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

ac

- full power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

ac

- 60 Hz . . . . . . . . . . . . . . . . . . 36

ac

- 50 Hz . . . . . . . . . . . . . . . . . . . 36

ac

- 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

ac

- 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

ac

- 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

ac

- 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

ac

60 Hz - full load - line 1 peak detector . . . . . . . . . . . . . . 40

ac

60 Hz - full load - line 2 peak detector . . . . . . . . . . . . . 40

ac

50 Hz - full load - line 1 peak detector . . . . . . . . . . . . . . 41

ac

50 Hz - full load - line 2 peak detector . . . . . . . . . . . . . 41

ac

- 60 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 38

ac

- 50 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . 38

ac

- 60 Hz . . . . . . . . . . . . . . 36

ac

- 50 Hz . . . . . . . . . . . . . . 36

ac

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

SCI communication is considered as an option.

MASTER UNIT

SCI

Communication

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

MASTER UNIT

ACíDC

ACíDC

ADAPTE R

ADAPTE R

6/42

AN2708 High-frequency ballast

2 High-frequency ballast

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

Figure 3. Ballast schematic

5VDD

9

+1+3+5+7+

IC_GND

+2+4+6+8+

SIGN

IC_GND

IC_GND

0

R64

R63

CON7

IC_GND

5VDD

D17

2K49

1%

1%

2K49

19

20

OSC1/CLKIN

U11

VSS1VDD2RESET3SS/AIN0/PB04SCK/AIN1/ PB15MISO/AIN2/PB26MOSI/AIN3/PB37CLKIN/AIN4/PB48AIN5/PB59DALIIN/AIN6/PB6

IC_GND

Reset

R62

4

U10

112

R61

11K

BAS16

4

U9

112

J5

ICP Connector

10

Reset

PWM0

IC_GND

13

12

14

16

11

17

18

OSC2

PA0(HS)/LTIC

PA7/DALIOUT

PA1(HS)/ATIC

ST7FDALIF2M6

PA4(HS)/ATPWM2

PA3(HS)/ATPWM115PA2(HS)/ATPWM0

PA6/MC0/ICCCLK/BREAK

PA5(HS)/ATPWM3/ICCDATA

10

R70

1k 1%

R69

1k 1%

PB1

C45

100nF

4K7

1%

5VDD

334

SFH6156-2

2

1%

334

SFH6156-2

2

IC_GND

PB2

EN2

EN1

0

R68

50V

IC_GND

PIN3 SFH6156-2

R67

10K

1%

IC_GND

PIN3 SFH6156-2

D18

BZX284C 2V7

0.5W

Q4

BC817-25

312

R66

4R7

1%

R65

+

R72

3K16

1%

1%

332R

C46

22uF

20V

R71

1K21

1%

1600V

C20

8.2nF

C21

100nF

250V

1
23

Lamp2

T8 36W

1W

R30_2

100K

250V

C17

100nF

18

18

R30_1

100K

1W

L1

L2

1.8mH

1.8mH

213

Q2

16

C14

100nF

630V

C11

1nF

R17

22E 1W

Rs= max 5 ohm @100kHz

C10

4.7nF

R14

10E

DZ1

15V

On Air On Air

D3

1N4148

R9

750K

1%1%

D2

STTH1L 06

8 1

T1

5 4

TRANSFORMER

R6

R4

180K

R1

750KR2750K

VS

12

IC_GND

C19

100nF

0.5W

IC_GND

+

IC_GND

50V

C7

4.7uF

R10

750K

1%

IC_GND

C5

100n

R8

12K

C4

1000n

68K

PB2

R5

180K

1%

C1

R26_2A

R26_1

750K

STP8NM50

R21

10E

15

HVG

VBOOT

RPRE2OPIN+

R12

120K

1

C3

2

5

U1

100nF

BRIDGE

432

180K

R26_2

750K

R15

10K

IC_GND

23

R7

INV

330n

W08G

1

FUSE

4A/250V

Line

J1

1
23

SIGN

7

C6

+

33E

COMP

ZCD

VCC

8

C18

8.2nF

Lamp1

T8 36W

R27_2

750K

R27_1

750K

213

Q3

STP8NM50

R22

10E

14

OUT

U2

L6574

OPIN-6OPOUT5RING

C9

400V

47uF

Q1

STP8NM50

1

7

CS

GD

GND

U1

L6562

MULT

3

C2

R3

-+

NTC

15E@25° 3A

Neutral

123

CON3

4

1600V

4

LVG11EN18EN2

100nF

4

6

10nF

10K

1%

R29_2

15K

R29_1

15K

R24_2

680K

R28_2

4.7K

L1&L2: Choke Induc t or

- E25x13x7 core

- 2.62mm gap f or 1.8mH indu ct a nce

- 267 turns (AWG 40)

R24_1

680K

4.7K

R28_1

IC_GND

D5 BAT46

D7 BAT46

R23

330E

R20

D11

1N4148

EN1

EN2

9

GND

CPRE

CF

4

R1668K

D4

1N4148

R11

1%

9.53K

RS2

0.82E

1W

RS1

0.82E

1W

R13

47K

D6 BAT46

RS_2

1E

0.6W 0.6W

RS_1

1E

1K

+

IC_GND

C15

D8

1N4148

330uF 25V

IC_GND

10

R1910K

IC_GND

C13

PWM0

1000nF 25V

1

3

Rf

15K

C12

470pF

IC_GND

R18

68K

IC_GND

Rup

120K

C8

IC_GND

600V 1A

D14

STTH1L06

T1: Boost Inductor Spec (ITACOIL E2543/E)

- E25x13x7 core, 3C 85 f errite

- 1.5mm gap f or 0.7mH prim ar y inductanc e

- Primary: 105 turns (20 x 0.1mm)

- Secondary: 11 t ur ns (0 . 1m m )

SIGN

D61

BAT46

D9 BAT46

68K

1%

R100

D10

BAT46

PB1

R25

470E

IC_GND

C16

10nF 25V

J2

1234567

EN2

EN1

5VDD

PB2

+

Cf

Rlow

100nF

SIGN

50V

4.7uF

IC_GND

4.7K

5VDD

IC_GND

1

IC_GND

VOUT

GND

2

VIN

U7 LE50CZ

3

Cout

+

95mA

L3

1.8mH

CVdd

10uF 25V

+

2

Cfb

S1S

DZ2

15V 0.5W

22nF 25V

FB

3

Vdd

4

D5D6D7D

8

+

L4

680uH

240mA

+

D15

1N4007 1A 1000V

HSMG-C670

GREEN

LD2

5VDD5VDD

LD1

RED

HSMS-C670HE

C44

100nF

50V

C43

1uF

16V

+

5VDD

IC_GND

C72

33nF

50V

IC_GND

C73

50V

68pF

J4

1234567

PB2

EN1

EN2

5VDD

PWM0

CON7

3

-+

IC_GND

142

D16

MB2S

Vss_STDALI

C42

2.2uF16V

+

D12

18V 0.5W

10uF 25V

D13

STTH1L 06

600V

1A

U8 Viper12A

Cin2

3.3uF 450V

Cin1

3.3uF 450V

R60

1

2

J3

DALI Bus

CON2

Vss_ST7DALI

5VDD

7/42

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. Ta bl e 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

4GND

55 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

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 Rs

C12 470 pF 50 V Ceramic cap

C13 1 µF 50 V Ceramic cap

C15 330 µF 25 V Electrolytic cap

100 nF 50 V Ceramic cap

= 5 Ω at 100 kHz

max

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

8/42

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

D3,D4,D8,D1

1

1N4148 Small signal rectifier 200 mA 100 V

STMicroelectronics ultrafast high voltage rectifier 1 A 600

V

D5,D6,D7,D9

, 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

L3 1.8 mH 95 mA Epcos BC series Axial inductor

L4 680 µH 240 mA Epcos LBC series Axial inductor

BAT46 DO 35 STMicroelectronics small signal Schottky diode

Choke inductor 2.62 mm gap, 267 turns (AWG40);

E25x13x7

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

9/42

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,

R29_2,Rf

R28_1,

R28_2,Rlow

R12,Rup 120 kΩ Resistor

R1,R2,R9,

R10, R26_1,

R26_2,
R27_1,

R27_2

R15,R19 10 kΩ Resistor

R3 10 kΩ 0.6 W 1% resistor

15 kΩ Resistor

4.7 kΩ Resistor

750 kΩ 0.6 W 1% resistor

R4,R5,

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

180 kΩ Resistor

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

10/42

AN2708 High-frequency ballast

Table 3. Ballast bill of material (continued)

Reference Value Description

R100 68 kΩ 1% SMD resistor 0805

R24_1,R24_

2

R30_1,R30_

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

U9,U10 SFH6156-2 Optocoupler

U11 ST7FDALIF2M6 SO20

680 kΩ Resistor

100 kΩ 2 W resistor

STMicroelectronics offline SMPS primary IC 730 V 0.4 A

27R

STMicroelectronics

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.

11/42

High-frequency ballast AN2708

The basic design specifications are listed in Tab le 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: f

sw

Maximum output voltage ripple: ∆Vo < ± 10 V

35 kHz

Maximum overvoltage admitted: ∆V

Expected efficiency: η

PFC

OVP

60 V

> 90 V

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 inTab le 5.

Table 5. Power stage design equations

Input capacitor (C1) Boost inductor Power MOSFET (Q1) Boost diode (D1)

C1

Irms

------------------------------- ---------------------------------------- -=

2π fsw r Vinrmsmin⋅⋅⋅

where

r 0.01 0.1÷=

Output capacitor (C6)

Volume 4K L I2irms⋅⋅≥

V2irms Vo 2 Virms⋅–()⋅

L

-------------------------------- --------------------------------------------- -=

where

2fswPi Vo⋅⋅⋅

K1410

⋅⋅≅

V

Vo ∆V

DSS

2

Pon I

Qrms

where

3–

Ie

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

Igap

I

Qrms

2 2 Iirms

OVP

⋅=

R

Vm inarg++=

DS on()

42

1

---------- -

---

9π

6

⋅–⋅⋅=

Virms

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

Vo

V

RRM

IF3Io⋅=

1.2 Vo⋅=

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

C6

≥

4π fVo∆Vo⋅⋅ ⋅

Po

Pcu

I2irms Rcu⋅⋅=

3

Pcross Vo Iirms t

⎛⎞

Pcap 3.3Coss V

⎝⎠

4

---

12/42

⋅⋅⋅=

fallfsw

1.5
drain

1

-- -

Cd V2drain⋅+⋅

2

P

lossesVTIDC

fsw⋅=

Rd I2rms⋅+⋅=

AN2708 High-frequency ballast

Table 6. L6562 biasing circuitry design equations

Pin 1 (INV) Pin 2 (COMP) Pin 3 MULT Pin 4 (CS)

∆OVP R

V

out

high

R

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

2.5

⋅=

6–

40 10

⋅⋅=

+()

highRlow

R

low

A RC-C network is
placed between this
pin and pin 1, leading
to a low crossover
frequency (some tens
of hertz) as well as to
an adequate phase
margin.

A small capacitor of 10 nF
filters the signal on MULT pin.

V

MULTpkx

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

Rlow

250 106–⋅

R

low

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

R

+

lowRhigh

-------------------------------- --------------- -=

2V

⋅

2.5

----------------------------- -==

250 106–⋅

2.5

inrmsmax

R

sense

Pin 5 (ZCD) Pin 6 (GND) Pin 7 (GD) Pin 8 Vcc

The supply voltage is
provided by a capacitive
power supply connected to
the half-bridge inverter.

R

start

Vout 2 V

m

--------------------------------- ---------------------------------------=

R6

≥

⋅–()

2.1 1.15⋅

Vout 2 V

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

⋅–()

m310

⋅⋅

inrmsmax

inrmsmin

3–

IC ground. As a layout
hint, this pin has to be
kept separated from
power ground. All the
IC signals have to be
referred to this pin.

Gate driver.
A "bleeder" resistor between

the gate and the source is
used to avoid undesired
switch-on, without affecting
the power consumption.

The PFC preregulator performances are shown in the following graphs:

Figure 4. PFC performances at 230 Vac-50 Hz

V

⎛⎞

inrmsmin

1.65 2.5

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

≤

Pd Rs I

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

⋅

⋅

⎜⎟

V

⎝⎠

inrmsmax

22I

⋅⋅

inrms

2

⋅=

Qrms

V

inrmsmin

-------------------------------- --------------=

I

2⋅

startup

CH1 (yellow): rectified input voltage
CH2 (blue): input current

13/42