ST AN3159 APPLICATION NOTE

AN3159

Application note

STEVAL-ILH005V2: 150 W HID electronic ballast

Introduction

This application note describes a two-stage electronic ballast for 150 W HID metal halide lamps. The ballast is made up of a boost converter (power factor controller - PFC) working in transition mode and an inverter made up of a full bridge that drives the lamp at low frequency square wave.

The ballast was developed for 185÷265 VAC 50/60 Hz input mains and is able to drive 150 W metal halide and high pressure sodium lamps.

All lamp phases have been analyzed and some design criteria are given with the test results.

Figure 1. STEVAL-ILH005V2 image

April 2011

Doc ID 17125 Rev 1

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www.st.com

Contents	AN3159

Contents

1	General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 4
2	Lamp power calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 6
3	Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		8
	3.1	Electrical schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
	3.2	Board layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	3.3	Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12
4	PFC section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		16
	4.1	Input specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	4.2	Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	4.3	Power components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	4.4	L6562A biasing circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
5	ST7 microcontroller application pins utilization . . . . . . . . . . . . . . . . .		23
6	Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		27
7	Lamp data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		28
8	Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		29
	8.1	Lamp ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
	8.2	Warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	30
	8.3	Burn phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31
	8.4	PFC section measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31
	8.5	Ballast efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	32
	8.6	Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	32
	8.7	Conducted emission pre-compliant tests . . . . . . . . . . . . . . . . . . . . . . . . .	33
9	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		34
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		35

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AN3159	List of figures

List of figures

Figure 1. STEVAL-ILH005V2 image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. 150 W HID ballast block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Figure 3. Inductor current during charge phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Figure 4. Inductor current during discharge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 5. PFC and auxiliary power supply electrical schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 6. Full bridge electrical schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 7. STEVAL-ILH005V1: control section electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 8. Board layout: top view (not to scale). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 9. Board layout: bottom view (not to scale). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 10. ST7FLITE39F2 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 11. MCU reference voltage circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 12. Pin utilization and reset circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 13. VBUS measurement circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 14. VLAMP measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 15. Rsense circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 16. Current regulation circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 17. Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 18. Lamp ignition voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 19. Lamp current and voltage during warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Figure 20. Steady-state phase: lamp current, voltage, and lamp power . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 21. STEVAL-ILH005V1 efficiency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 22. Peak measurement: line wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 23. Peak measurement: neutral wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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General circuit description	AN3159

1 General circuit description

The block diagram of the ballast is shown in Figure 2. The complete circuit is made up of two stages:

●The boost converter which regulates the DC bus voltage and corrects the power factor

●The inverter stage made up of a full bridge that converts the DC current coming from the PFC stage into an AC current for the lamp.

The operation mode of the full bridge realizes a buck converter. The full bridge also supplies the igniter block to generate the high-voltage pulses.

Figure 2. 150 W HID ballast block diagram

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To generate a square wave current in the lamp, the circuit is driven in the following way (see

Figure 3):

1.When low side device L2 is switched ON, the high side power MOSFET H1 operates with a high-frequency pulse width modulation (PWM). The duty cycle D is established by a constant-current control circuit.

Figure 3. Inductor current during charge phase

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4/36	Doc ID 17125 Rev 1

AN3159	General circuit description

In this condition the inductor current increases linearly and the voltage across the inductor L is:

Equation 1

VL = Vdc – VLAMP

where:

●VL= lamp voltage

●VDC = DC bus voltage

●VLAMP = lamp voltage

2.When the high side device H1 is switched OFF, the current flows in the low side devices (see Figure 4 below).

Figure 4. Inductor current during discharge phase

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The voltage across the inductor L is:

Equation 2

VL = –VLAMP

The current through L decreases linearly. In this way the circuit works as a rectifier buck converter.

The circuit operates in mode A and B complementary in low frequency supplying the lamp with low frequency square wave alternate current.

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Lamp power calculation	AN3159

2 Lamp power calculation

The lamp power is obtained by multiplying the lamp voltage signal for the lamp current.

The lamp voltage is sensed directly across the lamp. The lamp current is obtained by means of the relations reported below.

In continuous mode the lamp current is coincident with average inductor current. Starting from peak inductor current the average value is:

Equation 3

ILAMP	= IAV= Ipeak	I
		– -----
		2

where:

●ILAMP = lamp current

●IAV = inductor average current

●Ipeak = inductor peak current

●I = inductor current ripple

The ripple current in a buck converter in continuous mode is expressed as:

Equation 4

I = Vbus ×δ×(1−δ)

f L

where:

●Vbus = DC bus voltage

●L = inductance value

●ƒ = switching frequency

●δ = duty cycle

For the buck converter in continuous mode the duty cycle relation is:

Equation 5

δ	VLAMP
	= -----------------
	VBUS

In the relation (Equation 4) substituting (Equation 5) it is possible to obtain:

Equation 6

I =	1		×V	×(V	−V	)
2 2 f L			LAMP	BUS	LAMP
		VBUS

Assuming VBUS and f are constant it is possible to write:

Equation 7

K =	1
	2 f L V
	bus

6/36	Doc ID 17125 Rev 1

AN3159	Lamp power calculation

The equation (Equation 3) can be written as:

Equation 8

ILAMP =Ipeak −K×VLAMP ×(VBUS −VLAMP)

This relation is valid because the average current is equal to the lamp current.

This formula is implemented in the ST7 microcontroller in order to calculate the lamp current and regulate the lamp power.

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AN3159	Board description

3.2Board layouts

Figure 8. Board layout: top view (not to scale)

Figure 9. Board layout: bottom view (not to scale)

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