ST AN2524 Application note

AN2524

Application note

54 W / T5 ballast driven by the L6585D

Introduction

This application note describes a demo board able to drive a 54 W linear T5 fluorescent
lamp.

The ballast control is done by the L6585D that integrates PFC and half-bridge control
circuits, the relevant drivers, and the circuitry able to manage all lamp operating phases
(pre-heating, ignition and run mode).

Protections against main failures (lamp disconnection, anti-capacitive mode, PFC over­voltage) are guaranteed and obtained with a minimum number of exte rnal components

After the circuit description, a short overview of the ballast performances is presented.
Fluorescent lamps are driven more and more by electronic, rat her than electromagnetic

ballast primarily because fluorescent lamps can produce around 10% more light for the
same input power when driven above 20 KHz instead of 50/60 Hz. Operation at this
frequency also eliminates both light flickering (the response time of the discharge is too slow
for the lamp to have a chance to extinguish during each cycle) and audible noise.

An electronic ballast consumes less power and th erefore dissipates less heat than an
electromagnetic ballast. The energy saved can be estimated in the range of 20-25% for a
certain lamp power.

Finally the electronic solution allows better control of the filament current and lamp voltage
during pre-heating with the unquestionable benefit of increasing the mean lamp life.

Among electronic solutions for ballasts, ST proposes a new IC - the L6585D - t hat,
embedding both the PFC and half-bridge control sections, allows designing a compact and
reliable ballast with a minimum number of external components.

Figure 1. Evaluation board

May 2007 Rev 1 1/11

www.st.com

Contents AN2524

Contents

1 Application specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Board performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 3.1 PFC over-voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2 PFC open loop (feedback disconnection) . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3 Choke saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.4 Ignition voltage increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.5 Lamp power increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.6 Lamp disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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AN2524 Application specifications

1 Application specifications

This board has been designed in order to drive a T5 54W lamp with the following
characteristics:

Table 1. T5 – 54 W lamp characteristics

Input

voltage [V

188 to 264 50 54 400 0.455 120

AC

]

Mains

freq. [Hz]

Lamp

power [W]

Nom. Ignition

voltage [V]

Lamp

current [A]

Lamp

voltage [V]

The board performs the lamp control in all operating phases as well as a PF pre-regulator
stage. It also provides the following protections:

● PFC over voltage;

● PFC feedback disconnection;

● PFC choke saturation

● Lamp disconnection;

● Half-bridge anti-capacitive mode;

● High filament detection

Table 2. Schematic and part list

Ref. Value

BR1 DF06S
R1, R2 3.6 M
R3, R4 910 K

R6 42.2 K
R9 13.3 K

R10, R11 820 K

R12 1.2 M

R13 47

R14 47 K

R15 62 k

R16 56 k

R17, R18 47

R19 0.82, 1 W

R20 10

R22 0.82, 1/2 W

R23 330

R26, R27 680 K
R30, R33 240 K

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Application specifications AN2524

Table 2. Schematic and part list (continued)

Ref. Value

R35 1 Mohm

R36, R37 510 K

R38 12 K

R5, R8, R24, R25, R34 n.c.

R7, R21, R28, R29 short

C1 22 µF, 450 V, EPCOS B43888A5226M9

C2, C19, C23 10 nF

C3 n.c.
C4 470 nF
C5 680 nF

C6, C7 1 nF, 1 KV

C8 330 nF

C9 470 nF, 630 V, EPCOS B32652
C10 4.7 nF, 2 kV EPCOS B32653
C11 1 nF, 630 V
C12 470 pF
C13 100 nF, 250 V

C13b short
C14, C15 100 nF, X2, 275 Vac, EPCOS
C16, C17 100 nF

C18 10 µF, 35 V
C20 1 nF
C24 330 nF

C21, C22 n.c.

T1 E25, 2.1 mH, EPCOS B78313P7580A005 (T2363 51-03)

T2

F1 2 A fuse

RT1 NTC, 16R

D1 STTH1L06
D2 1N4148
D3 1N4148
D4 1N4148
D5 BZX84C15ZTX

L1 ITACOIL, 1.3 mH

39 mH, EPCOS

B82731M2601A 30

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