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 external components

After the circuit description, a short overview of the ballast performances is presented.

Fluorescent lamps are driven more and more by electronic, rather 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 therefore 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 - that, 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

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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		Mains	Lamp	Nom. Ignition	Lamp	Lamp
voltage [VAC]		freq. [Hz]	power [W]	voltage [V]	current [A]	voltage [V]
188 to 264		50	54	400	0.455	120

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	39 mH, EPCOS
			B82731M2601A 30
		F1	2 A fuse
		RT1	NTC, 16R
		D1	STTH1L06
		D2	1N4148
		D3	1N4148
		D4	1N4148
		D5	BZX84C15ZTX
		L1	ITACOIL, 1.3 mH
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