STMicroelectronics AN2747 250 w hid metal halide electronic ballast Datasheet

AN2747
Application note
250 W HID metal halide electronic ballast
Introduction
This application note describes the two stages of electronic ballast for a 250 W HID metal
halide lamp. The ballast is composed of a boost converter (power factor controller PFC)
working in fixed OFF time and an inverter composed of a full bridge that drives the lamp at
low frequency square wave.
This design was realized thanks to the very large STMicroelectronics product portfolio. The
components include a PFC driver, half-bridge drivers, a microcontroller, an auxiliary power
supply, a voltage reference, logic parts, an amplifier, comparators, power devices as Power
MOSFETs, IGBTs, and fast diodes.
In the present note special attention has been given to the full bridge stage. The tests have
been conducted using a 250 W metal halide lamp HQI - T (OSRAM) and some design
criteria are given with test results. In the full bridge section all lamp phases have been
analyzed.
Figure 1.
May 2008
STEVAL-ILH001V1
Rev 1
1/44
www.st.com
Contents
AN2747
Contents
1
Lamp description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
2
3
Lamp phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.1
Ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.2
Warm-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.3
Burn phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2
Lamp power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1
Electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4
L6385 high-voltage high and low side driver . . . . . . . . . . . . . . . . . . . . 20
5
ST7LITE39 microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1
Application pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6
Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7
TS272 high-performance CMOS dual operational amplifiers . . . . . . . 28
8
LM119 high-speed dual comparators . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9
74AC00 QUAD2-input NAND gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
10
Lamp data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
11
PFC section design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12
Full bridge design criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.0.1
2/44
Inductor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.1
Filter capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.2
Igniter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
AN2747
13
Contents
12.3
Power MOSFET selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
12.4
IGBT selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
13.1
Init phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
13.2
Lamp ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
13.3
Warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
13.4
Burn phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
13.5
PFC run phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
13.6
Thermal measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
14
Firmware flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
15
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
16
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3/44
List of figures
AN2747
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
4/44
STEVAL-ILH001V1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Lamp families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Luminous efficiency of various lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
HID lamps operation frequency: high pressure sodium lamps - acoustic resonance duty
frequency map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
HID lamps operation frequency: metal halide lamps - acoustic resonance duty frequency
map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Instantaneous lamp power with sinusoidal and square waveforms . . . . . . . . . . . . . . . . . . . 7
HID warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
250 W HID lamp ballast - block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Inductor current during charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Inductor current during discharge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
PFC electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Full bridge electrical schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Control board electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Power board layout (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Control board layout (not to scale) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
L6385 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
ST7FLIT3xB general block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
ST7FLITE39 pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
MU reference voltage circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Pin usage and reset circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Vbus measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Lamp voltage sensing circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Lamp voltage measurement circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Constant current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Rsense circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Current regulation circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Auxiliary power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
LM119 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
74AC00 pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Eye sensitivity versus frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Igniter circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Full bridge init phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Lamp ignition voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Lamp current and voltage during warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Warm-up phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Steady state phase: lamp current, voltage and lamp power . . . . . . . . . . . . . . . . . . . . . . . . 39
Steady state phase: lamp current, voltage and lamp power . . . . . . . . . . . . . . . . . . . . . . . . 39
Ballast efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Firmware flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
AN2747
1
Lamp description
Lamp description
New products and devices are being launched in lighting applications and new solutions for
these applications are required. High intensity discharge (HID) lamps have become
attractive lighting sources for their luminous efficacy and their long life. Figure 2 illustrates
the families of electric lighting for which HID lamps are intended.
Figure 2.
Lamp families
LAMPS
INCANDESCENT
CONVENTIONAL
HALOGEN
GAS-DISCHARGE
SODIUM
MERCURY
LOW
PRESSURE
HB LEDs
HIGH
PRESSURE
CFL/TL
HID
In this document we will refer to high pressure sodium and mercury lamps as HID lamps.
Figure 3 shows the luminous efficiency for each lamp type.
Figure 3.
Luminous efficiency of various lamps
5/44
Lamp description
AN2747
Referring to Figure 3 we can see that HID lamps have higher luminous efficacy, but some
negative aspects must be considered.
When comparing HID and fluorescent lamps, two important issues should be considered: a
greater starting voltage and the presence of acoustic resonance.
To solve the issue of higher HID ignition voltage, a sort of starting aid, called igniters, are
used to ignite the lamp.
The problem of acoustic resonance is more complex. Acoustic resonance is characteristic of
HID lamps operating at frequencies greater than 1 kHz and appears when lamp power
fluctuation exceeds a threshold value.
The current/voltage lamp waveforms and the operating frequency cannot be chosen freely,
but they are dependent on lamp type, condition and temperature. A wrong choice of
frequency and/or waveform can have a very negative effect on lamp performance and/or
lifetime and sometimes the discharge tube may be mechanically damaged.
Figure 4.
Figure 5.
HID lamps operation frequency:
high pressure sodium lamps acoustic resonance duty frequency
map
~1MHz
~1kHz
Frequency
Stable
Unstable
HID lamps operation frequency:
metal halide lamps - acoustic
resonance duty frequency map
~1MHz
~1kHz
Frequency
Stable
Unstable
As shown in Figure 4 and 5 for different lamps the free bands are completely different.
●
For HID lamps the solution proposed to avoid acoustic resonance uses the same
principle. The designer must avoid a combination of power fluctuation and operating
frequency . Another parameter that must be taken into account is flickering. For this
reason, the frequency used in the application is higher than 100 Hz and below 1 kHz.
For sinusoidal waveforms the instant lamp power is variable and it has twice the frequency
of the voltage and current frequency. In Figure 6 a diagram of instantaneous power for
different waveforms is shown.
6/44
AN2747
Lamp description
Figure 6.
Instantaneous lamp power with sinusoidal and square waveforms
Instantaneous Power
Current
Voltage
Instantaneous Power
Voltage
Current
For ideal square waveforms, the instant power delivered to the lamp is constant and not
modulated by any frequency. This driving plus the low frequency driving allows obtaining a
system that is immune to the problem of acoustic resonance.
For this reason HID lamp applications using square wave current techniques are the best
solution.
1.1
Lamp phases
1.1.1
Ignition phase
The ignition voltage for HID lamps is higher with respect to the mains voltage. The peak
voltage value to initiate the discharge is very high. Typically this is about 3 kV ÷ 5 kV.
The voltage level at which an HID lamp ignites is called "ignition voltage". This voltage level
is referred to the lamp when it is cold but this value increases with lamp temperature.
To ensure immediate HID lamp restart, called “hot restrike”, very high re-ignition peaks are
necessary (about 20 kV).
Standard luminaries are not designed for hot restrike voltages. For this reason in order to
obtain hot lamp re-ignition, several minutes must elapse for the lamp to cool. The restart
time depends on lamp temperature.
1.1.2
Warm-up
When the discharge has been initiated by the starting gas and the lamp still does not burn
properly, a warm-up time is required.
During the warm-up time the gas temperature increases, increasing the light output. The
lamp voltage starts approximately from a quarter of Vlamp and increases up to Vlamp.
7/44
Lamp description
AN2747
During this phase the maximum current must be limited and maintained at a value higher
than 30% of the nominal value. The time to reach 80% of full light/power is called “warm-up
time”. HID lamps have a warm-up time of approximately 2-5 minutes.
In Figure 7 typical behaviors of lamp voltage and current during warm-up is shown.
Figure 7.
1.1.3
HID warm-up phase
Burn phase
After the warm-up phase when the lamp reaches nominal power, the lamp current must be
regulated taking into account the lamp voltage to ensure fixed rated power.
8/44
AN2747
General circuit description
2
General circuit description
2.1
Block diagram
The block diagram of the ballast is shown in Figure 8. The complete circuit is composed of
two stages:
●
The boost converter which regulates the output voltage and performs the power factor
correction.
●
The inverter stage composed 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 synchronous buck converter. The full bridge
moreover drives the igniter block to generate the high-voltage pulses.
Figure 8.
Main
250 W HID lamp ballast - block diagram
STTH8R06DIRG
Filter
+
Bridge
STP20NM50FD
IGNITER
L6385
L6385
STF12NM50N
L6562
Lamp
STGF10NB60SD
VIPER12
ST7FLITE39
74AC00
LM119
TS272I
LE50AB
To generate a square wave current in the lamp, the circuit is driven in the following way:
a)
Figure 9.
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.
Inductor current during charge phase
DC Bus
ON
I
H2
H1
Lamp
L
L1
ON
L2
In this condition the current increases linearly and the voltage across the inductor L is:
9/44
General circuit description
AN2747
Equation 1
V L = V dc – V lamp
where
●
VL= lamp voltage
●
Vdc = DC bus voltage
●
Vlamp = lamp voltage
b)
When the high side device H1 is switched OFF, the current flows in the low side
devices. The freewheeling diode integrated in the low side device IGBT L1
operates at high frequency with duty cycle 1-D (see Figure 10).
Figure 10. Inductor current during discharge phase
DC Bus
OFF
I
H2
H1
L
Lamp
ON
L2
L1
The voltage across the inductor is:
Equation 2
V L = – V lamp
The current through L decreases linearly. This circuit is actually a synchronous rectifier buck
converter. To minimize the current ripple through the lamp, the circuit operates in continuous
conduction mode (CCM) with fixed frequency.
The circuit operates in mode A and B complementarily in low frequency supplying the lamp
with square wave alternate current.
2.2
Lamp power management
The lamp power is obtained by multiplying the lamp voltage signal and the lamp current.
The lamp voltage is sensed directly across the lamp while the lamp current is obtained using
the relation given below. In continuous mode the lamp current is coincident with average
buck coil current. Starting from peak inductor current the average value is:
Equation 3
∆I
I lamp = I AV = I peak – ----2
10/44
AN2747
General circuit description
where
●
Ilamp = lamp current
●
IAV = average current
●
Ipeak = inductor peak current
●
∆I = inductor current ripple
The ripple current in a buck converter working in continuous mode is expressed as:
Equation 4
V bus
∆I = ------------ ⋅ δ ⋅ ( 1 – δ )
f⋅L
where
●
Vbus= DC bus voltage
●
L= inductance value
●
f= switching frequency
●
ζ= duty cycle
For the buck in continuous mode the duty cycle relation is:
Equation 5
V lamp
δ = -------------V bus
Using the relation (Equation 4) in the equation (5) we obtain:
Equation 6
1
∆
-----I = ---------------------------------- ⋅ V lamp ⋅ ( V bus – V lamp )
2 ⋅ f ⋅ L ⋅ V bus
2
Assuming Vbus and f constant it is possible to write:
Equation 7
1
K = --------------------------------2 ⋅ f ⋅ L ⋅ V bus
The relation (Equation 3) can be written as:
Equation 8
I lamp = I peak – K ⋅ V lamp ⋅ ( V bus – V lamp )
This relation is valid because the average current is equal to the lamp current. This formula
is implemented in the microcontroller in order to calculate the lamp current.
11/44
Board description
3
Board description
The detailed electrical schematics are given in the following figures.
3.1
Electrical schematic
Figure 11. PFC electrical schematic
12/44
AN2747
AN2747
Board description
Figure 12. Full bridge electrical schematic
13/44
Board description
Figure 13. Control board electrical schematic
14/44
AN2747
AN2747
Board description
Figure 14. Power board layout (not to scale)
Figure 15. Control board layout (not to scale)
15/44
Board description
3.2
AN2747
Bill of material
Table 1.
16/44
PFC bill of material
Name
Value
Rated
Type
C1
1 µF
400 V
polyester capacitor
C2
10 nF
50 V
ceramic
C5
1 µF
50 V
ceramic
C6
330 pF
50 V
ceramic
C7
560 pF
50 V
ceramic
C8
470 nF
630 V
EPCOS B32523Q8474K
C9
220 µF
450 V
EPCOS electrolytic capacitor
B43504-B5227-M7
C10
330 pF
50 V
ceramic
C11
22 nF
50 V
ceramic
C12
47 µF
35 V
Electrolytic
C13
100 nF
50 V
ceramic
C14
10 µF
50 V
Electrolytic
CX1, CX2
330 nF
275 V
EPCOS X2 capacitor
B32922A2334K
D2, D3, D4, D13
200 mA
100 V
Signal diode
D5A
3 A, 600 V
General purpose rectifier
D6
STTH8R06DIRG
STMicroelectronics
D8
8 A 1000 V
Bridge rectifiers
D9
Zener diode
15 V 1/2 W
D10
STTH1L06
1 A, 600 V
STMicroelectronics
D11
STTH1L06
1 A, 600 V
STMicroelectronics
D13
1N4148
F1
FUSE
250 V 8 A
L1
2 x 6.8 mH
4 A 250 V
L2
550 µH 4 A
L3
2.2 mH
M1,M2
STF12NM50N
STMicroelectronics
NTC1
S237
EPCOS B57237S0259M
R1
330 Ω
1% 1/4 W
R2A R2B
680 kΩ
1% 1/4 W
R3
10 kΩ
1% 1/4 W
EPCOS Common mode chokes
B82725-J2402-N20
Magnetica part number
1555.0009
AN2747
Board description
Table 1.
PFC bill of material (continued)
Name
Value
Rated
R5
6.8 kΩ
1% 1/4 W
R6
6.8 Ω
1% 1/4 W
R7A,R7B,R7C,R7D
0.68 Ω
1% 1/4 W
R8
1.5 kΩ
1% 1/4 W
R9
12 kΩ
1% 1/4 W
R10A
470 kΩ
1% 1/4 W
R10B
560 kΩ
1% 1/4 W
R11
6.8 kΩ
1% 1/4W
R12
12 kΩ
1% 1/4 W
R13
6.8 Ω
1% 1/4 W
TR1
BC557
TO92
U1
L6562
STMicroelectronics
U2
VIPer12AS-E
STMicroelectronics
Table 2.
Type
Full bridge bill of material
Name
Value
Rated
Type
C100,C101
100 pF
630 V
C102, C103
10 µF
25 V
C104, C106
3.3 µF
50 V
EPCOS polyester capacitor
B32529-D5335-K000
C105, C107
33 pF
50 V
ceramic
C108,C109
68 pF
50 V
ceramic
C110
100 nF
400 V
EPCOS B32652A6104K
C111
680 nF
630 V
EPCOS B32523Q8684K
C112
220 pF
6 KV
Murata DECB33J221KC4B
C113,C114,C115
68 pF
50 V
ceramic
D100,D101,D102,D103
200 mA
100 V
Signal diode
D104,D105
STTH1L06
L100
800 µH
Q100,Q102
STP20NM50FD
STMicroelectronics
Q101, Q104
STGF10NB60SD
STMicroelectronics
R102
470 mΩ
1% 2 W
R103
820 kΩ
1% 1/4 W
R104,R106,R108,
R110
100 Ω
1% 1/4 W
STMicroelectronics
3.5 A
Magnetica part number 1775.0001,
VOGT: SL0607112101
17/44
Board description
AN2747
Table 2.
Full bridge bill of material (continued)
Name
Value
Rated
R105, R109
22 Ω
1% 1/4 W
R111
820 kΩ
1% 1/4 W
R112, R115
10 kΩ
1% 1/4 W
R113
15 kΩ
3W
R114, R116
47 kΩ
1% 1/4 W
R117, R118
1 MΩ
1% 1/4 W
T100
High voltage
Transformer
N1/N2=55/3
VOGT part number SL0607111102
U100
SPARK GAP
235 V
EPCOS B88069X4290T502
U101, U102
L6385
Z1,Z2
Zener diode
Table 3.
18/44
Type
STMicroelectronics
16 V 1/2 W
Control board bill of material
Name
POS
Rated
Type
C2
100 nF
C3
10 µF
C4
100 nF
SMD 1206
C5,C8,C9
0.1 µF
SMD 1206
C6
0.47 µF
SMD 1206
C7
2.2 µF
SMD 1206
C11
22 pF
SMD 1206
C17, C18
1 nF
SMD 1206
C19,C20
1 µF
SMD 1206
D1,D2
BAT42
STMicroelectronics
LD2
Green LED
SMD 1206
LD3
Red LED
SMD 1206
R2
47 kΩ
SMD 1206
R5,R6
100 kΩ
SMD 1206
R7
5.6 kΩ
SMD 1206
R9
4.7 kΩ
SMD 1206
R10,R15,R20
1 kΩ
SMD 1206
R11,R12
10 Ω
SMD 1206
R3,R4,R8,R14,R17,
R18,R19,R21,R22, R26
10 kΩ
SMD 1206
R23,R27
470 Ω
SMD 1206
SMD 1206
15V
through hole
AN2747
Board description
Table 3.
Control board bill of material (continued)
Name
POS
Rated
Type
R24
R25
U1,U2
74AC00
STMicroelectronics
U3
LM119
STMicroelectronics
U4
TS272
STMicroelectronics
U5
STF7LITE39B
STMicroelectronics
U6
LE50-CD
V1
100 kΩ
5 V 100 mA
STMicroelectronics
19/44
L6385 high-voltage high and low side driver
4
AN2747
L6385 high-voltage high and low side driver
Figure 16. L6385 block diagram
The L6385 is a high-voltage device, manufactured with BCD "OFF-LINE" technology. It has
a driver structure that enables to drive independently referenced N-Channel Power
MOSFETs or IGBTs. The upper (floating) section is enabled to work with voltage rail up to
600 V. The logic inputs are CMOS/TTL compatible for easy interfacing with controlling
devices.
The main characteristic of this driver are:
20/44
●
high-voltage rail up to 600 V
●
dV/dt immunity ± 50 V/nsec in full temperature range
●
driver current capability: 400 mA source, 650 mA sink
●
switching times 50/30 nsec rise/fall
●
with 1 nF load
●
CMOS/TTL Schmitt trigger inputs with hysteresis and pull-down
●
undervoltage lockout on lower and upper driving sections
●
internal bootstrap diode
●
outputs in phase with inputs
AN2747
5
ST7LITE39 microcontroller
ST7LITE39 microcontroller
The ST7LITE3 is a member of the ST7 microcontroller family of products. All ST7s are
based on a common 8-bit core, able to run up to 8 MHz clock frequency. Enhanced
instructions like an 8x8-bit unsigned multiplication and indirect addressing allow good
efficiency and a compact application code.
Figure 17. ST7FLIT3xB general block diagram
The MCU main characteristics are:
●
internal RC oscillator with 1% precision at 8 MHz CPU frequency
●
seven input channels 10-bit resolution A/D converter with 3.5 s of conversion time
●
two 8-bit lite timers with prescaler
●
two12-bit auto-reload timers with 4 independent PWM outputs and programmable dead
time generation
●
8 Kbytes flash program memory
●
384 bytes RAM
●
256 bytes data EEPROM
●
SPI and SCI communication interfaces
Figure 18 shows the ST7FLITE39 pinout.
21/44
ST7LITE39 microcontroller
AN2747
Figure 18. ST7FLITE39 pinout
5.1
Application pins
●
Pin 1: GND
●
Pin 2: VDD: main supply voltage. Power is supplied using an STMicroelectronics LE50
which is able to supply 5 V with ± 1% tolerance. Figure 19 shows the adopted circuit.
Figure 19. MU reference voltage circuit
22/44
AN2747
ST7LITE39 microcontroller
●
Pin 3: reset pin
Figure 20. Pin usage and reset circuit
●
Pin 4: ADC channel 0 analog input, to measure the main DC bus voltage (VBUS). A
resistor partition is used to obtain, starting from a +400 V of bus a maximum of 5 V,
compatible with the MCU voltage input, see Figure 23.
Figure 21. Vbus measurement circuit
●
Pin 5: ADC analog input 1: not used
●
Pin 6: ADC analog input 2: This pin is used to measure the lamp voltage. In Figure 23
there are two nets. The first one is a partitioning circuit composed of resistors R118R114, the other one composed of R117-R116. The voltage across the capacitors C114
and C115 is used as input of U4a to obtain a signal compatible with the MCU input.
23/44
ST7LITE39 microcontroller
AN2747
Figure 22. Lamp voltage sensing circuit
Figure 23. Lamp voltage measurement circuit
●
Pin 7: PB3 digital floating input with interrupt. This pin is used for maximum current
protection.
●
Pin 8: PB4 digital floating input. It is used for MCU Vref calibration.
●
Pin 9: push-pull output, used to drive two status leds. A green LED indicates the normal
status. A red LED indicates a fault condition (for example overcurrent protection).
●
Pin 10: SCI RXD, used for external communication, power line modem or PC
●
Pin 11: SCI TXD, used for external communication, power line modem or PC
●
Pin 12-13: PA6-PA5 not used
●
Pin 14: PA4 output PWM3. It is used to generate a reference voltage for the constant
current control.
The current signal is obtained through a sense resistor R102 (ILAMP signal Figure 25). This
voltage across R102 is amplified by U4b STMicroelectronics amplifier TS272 and it is
compared using the comparator LM119 with the reference voltage coming from the MCU.
When the Ilamp signal exceeds the defined threshold, the comparator output falls, giving the
reset signal to the drivers.
24/44
AN2747
ST7LITE39 microcontroller
Figure 24. Constant current control
Figure 25. Rsense circuit
●
Pin 15-16: PA3-PA2 output PWM1 and PWM0. These signals are connected to two flipflops realized using U1 and U2. These flip-flops are used to obtain the drive signal for
the high side switches, see Figure 25. The set signal is obtained by PWM rising edge,
directly from the signal PWM1 and PWM0. This signal is generated at 40 kHz fixed
frequency. The reset signal is obtained by the output comparator U3. In this way it is
possible to generate a PWM signal for drivers with fixed frequency and controlled duty
cycle. Since the system works in continuous conduction mode to avoid instability in the
current control circuit, the maximum duty cycle is limited at 50%.
25/44
ST7LITE39 microcontroller
AN2747
Figure 26. Current regulation circuit
26/44
●
Pin 17-18: PA1-PA0 push-pull outputs. These generate the signals for the low side
driver. They are directly connected to the L6385 low_side_input pins.
●
Pin 19-20: OSC2-OSC1 External quartz input: not used.
AN2747
6
Auxiliary power supply
Auxiliary power supply
The proposed power supply can be successfully applied in applications requiring 15 V for
the power switch gate driver. This circuit assures good performance in terms of size and
performance at very low cost.
It is based on the VIPer12A-E in nonisolated buck configuration. Figure 27 shows the
schematic.
Figure 27. Auxiliary power supply
The VIPer12A-E is a low-cost smart power device with an integrated PWM controller that is
suitable for such applications.
27/44
TS272 high-performance CMOS dual operational amplifiers
7
AN2747
TS272 high-performance CMOS dual operational
amplifiers
The TS272 devices are low cost, dual operational amplifiers designed to operate with single
or dual supplies. These operational amplifiers use the ST silicon gate CMOS process
allowing an excellent consumption-speed ratio. These series are ideally suited for lowconsumption applications.
Figure 28. Pinout
The main characteristics of this device are:
28/44
●
output voltage can swing to ground
●
excellent phase margin on capacitive loads
●
gain bandwidth product: 3.5 MHz
●
stable and low offset voltage
●
three input offset voltage selections
AN2747
8
LM119 high-speed dual comparators
LM119 high-speed dual comparators
These products are precision high-speed dual comparators designed to operate over a wide
range of supply voltages down to a single 5 V logic supply and ground and have low input
currents and high gains.
Although designed primarily for applications requiring operation from digital logic supplies,
the comparators are fully specified for power supplies up to ±15 V.
Figure 29. LM119 pinout
The main characteristics of this device are:
●
two independent comparators
●
supply voltage: +5 V to ±15 V
●
typically 80 ns response time at ±15 V
●
minimum fan-out of 2 on each side
●
maximum input current of 1 µA over operating temperature range
●
inputs and outputs can be isolated from system ground
●
high common-mode slew rate
29/44
74AC00 QUAD2-input NAND gates
9
AN2747
74AC00 QUAD2-input NAND gates
The 74AC00 is an advanced high-speed CMOS QUAD 2-INPUT NAND gate fabricated with
sub-micron silicon gate and double-layer metal wiring C2MOS technology. The internal
circuit is composed of 3 stages including buffer output, which enables high noise immunity
and stable output. All inputs and outputs are equipped with protection circuits against static
discharge, giving them 2 KV ESD immunity and transient excess voltage. Figure 30 shows
the device pinout.
Figure 30. 74AC00 pinout
The main characteristics are:
30/44
●
high speed: tPD = 4 ns (Typ.) at VCC = 5 V
●
low-power dissipation: ICC = 2 mA (max) at TA = 25 °C
●
high noise immunity: VNIH = VNIL = 28 % VCC (min.)
●
50 W transmission line driving capability
●
symmetrical output impedance: |IOH| = IOL = 24 mA (min.)
●
balanced propagation delays: tPLH at tPHL
●
operating voltage range: VCC (OPR) = 2 V to 6 V
●
pin and function compatible with 74 series 00
●
improved latch-up immunity
AN2747
10
Lamp data
Lamp data
The lamp data are given below and each is valid for the corresponding operating phase.
●
Ignition phase: The ignition voltage in case of a cold lamp is about 4-5 kV. The ignition
voltage increases with lamp temperature. The ignition voltage in case of a hot re-strike
can reach 25 kV. The circuit is not designed to supply this very high voltage pulse.
●
Warm-up phase: During this phase a high warm-up current must be supplied (30%
higher than nominal current) to prevent lamp turnoff. The lamp voltage increases
gradually starting from a quarter of nominal lamp voltage up to the nominal value. The
warm-up time is about 2 minutes. For a 250 W metal halide lamp a current of 3.2 amps
is applied.
●
Burn phase: The lamp is designed to be driven with a low frequency square wave AC
current to avoid acoustic resonance of the electric arc. Acoustic resonance occurs
approximately in the frequency domain: 1 kHz - 1 MHz. Some frequency ranges free of
acoustic resonance exist. The commutating frequency of the full bridge should be
limited to the domain: 50 Hz - 10 kHz to avoid any risk of acoustic resonance. In this
application the commutating frequency of 160 Hz has been chosen. This frequency has
been chosen in order to avoid a flickering effect. For frequencies higher than 130 Hz
eye sensitivity is practically zero. In Figure 31 a diagram of eye sensitivity is shown.
Figure 31. Eye sensitivity versus frequency
The nominal lamp voltage is approximately 100 V and the nominal lamp power is 250 W.
The differential resistance of the lamp is small and negative. To obtain a stable operating
point, impedance in series with the lamp is needed.
31/44
PFC section design criteria
11
AN2747
PFC section design criteria
For PFC design criteria see AN 1875.
12
Full bridge design criteria
The design of full bridge section involves the inductor (buck) component and device
selection.
12.0.1
Inductor design
The design specs are:
1.
lamp current
2.
lamp ripple current
3.
lamp voltage
4.
lamp ripple voltage
The design steps are summarized below:
1.
Fix the switching frequency fs and consequently the period Ts also is fixed. This
frequency for power application is in the range 20 kHz ÷ 100 kHz
2.
out
lamp
Fix the duty cycle estimation δ as δ = --------------= --------------
3.
Fix the current ripple in the inductor L
4.
Calculate the inductance value using the relation:
V
V input
V
V bus
Equation 9
V lamp ⋅ ( 1 – δ ) ⋅ T s
L = ----------------------------------------------∆I
For the inductance calculation:
●
fs = 40 kHz, Ts = 25 s
●
Vlamp =100 V
●
Vbus = 400 V
●
δ = 0.25
●
∆I = 2 A
Using these parameters the inductance value is 0.93 mH. For this project an inductance of
0.8 mH is used.
12.1
Filter capacitor
To calculate the capacitor value that is in parallel to the lamp, the max current lamp ripple
must be considered. The lamp current ripple must be limited in order to avoid acoustic
resonance. In this application the current ripple was fixed at ∆Ilamp ± 5% of nominal current
32/44
AN2747
Full bridge design criteria
Equation 10
∆V lamp = R lamp ⋅ ∆I lamp
where Rlamp can be obtained by the relation (in the hypothesis of linear value):
Equation 11
2
V lamp
R lamp = ----------------P lamp
Substituting this relation in the previous relation it is possible to obtain Vlamp.The relation to
calculate the output capacitor is:
Equation 12
∆I
C = ---------------------------------8 ⋅ f s ⋅ ∆V lamp
●
∆I= inductor current ripple = 2 A
In this case we have:
12.2
●
Ilamp =2.5 A
●
∆Ilamp = ± 5% Ilamp = ± 125 mA = 250 mA
●
Rlamp = 40 Ω
●
∆Vlamp = 10V
●
C= 625 nF. A capacitor of 680 nF 400 V was selected.
Igniter
For the design of the igniter the maximum ignition voltage must be considered. This ignition
voltage is obtained by charging a capacitor (100 nF) using a resistor. When the voltage
exceeds the gas spark gap threshold (235 V) capacitor is discharged in the primary winding
of the high voltage transformer. This voltage is transferred at the secondary winding and a
high voltage pulse is obtained, see Figure 32.
Figure 32. Igniter circuit
V > 235V
33/44
Full bridge design criteria
12.3
AN2747
Power MOSFET selection
For the selection of the Power MOSFET, the following rules must be considered:
●
●
VDSS > Vout
–
ID > IT(pk)
–
Vbus = 400 V
–
IT(peak) = 4 A
VDSS greater than 20% of Vbus that is 480 V
The STP20NM50FD, FDmesh™ Power MOSFET was selected because it satisfies the
following specifications:
●
VDSS: 500 V
●
RDS(on): < 0.25 Ω
●
ID: 20 A
This device was selected considering the losses in these devices which are are composed
of three parts: switch-on, conduction and switch-off losses.
The first loss is caused by the voltage across the MOSFET at switch-on, the second one
depends on RDS(on) and RMS current, and the last one is caused by the current at switchoff.
The general formulas for conduction and switch-off losses are given below:
Equation 13
P cond = I
2
RMS
⋅ RDS ( on ) ⋅ δ
Equation 14
P turn – off = V bus ⋅ I rms ⋅ t cross ⋅ f
12.4
IGBT selection
Considering the current level and the working frequency (160 Hz) the best choice for the low
side device is the IGBT device. In parallel at this power switch the freewheeling diode works
at high frequency in continuous conduction mode. Since the diode is stressed with high
di/dt, Trr, Qrr, and Irms became key parameters especially when power loss must be
minimized. For both reasons the STGF10NB60SD is the right choice for this application.
Using high voltage technology based on a patented strip layout, STMicroelectronics has
designed an advanced family of IGBTs, the PowerMESH™ IGBTs, with outstanding
performances. The suffix "S" identifies a family optimized with minimum on-voltage drop for
low frequency applications (<1 kHz).
●
VCes: 600 V
●
Vcesat(max): < 1.8 V
●
ID: 10 A
Moreover in the same package a fast diode is integrated with the following characteristics:
34/44
●
Trr(typ): 50 ns
●
Qrr(typ): 70 nC
AN2747
Full bridge design criteria
The power losses can be divided in two quantities: IGBT losses and diode losses. The IGBT
power losses are mainly due to the conduction phase and depend on Vcesat.
Equation 15
P IGBTcond = V ce ⋅ I F ( av )
In the diode the conduction losses (considering a duty cycle of 50%) can be estimated using
the following formula:
Equation 16
P Dcond = V to ⋅ I F ( av ) + rd ⋅ I
2
F ( rms )
Where:
●
PDcond= diode conduction losses
●
IF(av)= average forward current
●
IF(rms)= RMS forward current
35/44
Experimental results
13
AN2747
Experimental results
These results have been obtained at a rated input voltage of 230 V.
Ambient temperature: 23 °C.
In the full bridge section the following phases have been analyzed:
13.1
1.
init phase
2.
ignition phase
3.
warm-up phase
4.
steady state phase
Init phase
During this phase the DC bus voltage is sensed and both low side devices are switched ON.
In this way both bootstrap capacitors are charged. The init phase is shown below in
Figure 33.
Figure 33. Full bridge init phase
36/44
●
C1 = low side IGBT 1 gate voltage
●
C2 = low side IGBT 2 gate voltage
●
C3 = inductor current
●
C4 = lamp voltage
AN2747
13.2
Experimental results
Lamp ignition phase
The high voltage transformer generates a proper ignition voltage to ignite the lamp. The
voltage across the lamp is shown below in Figure 34.
Figure 34. Lamp ignition voltage
13.3
Warm-up phase
During this phase the lamp current is limited and the lamp voltage increases starting from a
quarter of nominal voltage until the rated voltage. During this phase the lamp power
increases and at 80% of nominal lamp power the control power is activated, regulating the
lamp power.
37/44
Experimental results
AN2747
Figure 35. Lamp current and voltage during warm-up phase
●
C2 = lamp current
●
C3 = inductor current
●
C4 = lamp voltage
Figure 36. Warm-up phase
13.4
Burn phase
During this phase the lamp is supplied with low-frequency square wave current. The lamp
current and the lamp power are maintained constant and some waveforms are shown in
Figure 37 and 38.
38/44
AN2747
Experimental results
Figure 37. Steady state phase: lamp current, voltage and lamp power
Figure 38. Steady state phase: lamp current, voltage and lamp power
13.5
PFC run phase
During the run phase the input power the power factor and the input current THD have been
measured. The results are given in Table 4.
39/44
Firmware flowchart
Table 4.
AN2747
Power factor and input current THD measurements
Vin (rms) V
Power factor
THD%
115
0.994
10
230
0.940
27
Below Figure 39 shows a diagram of total ballast efficiency versus input voltage. The system
efficiency is obtained as a ratio of lamp power to input power.
Figure 39. Ballast efficiency
13.6
Thermal measurement
In the output stage a thermal measurement on the power device has been performed. On
the devices a heat sink having thermal resistance Rth = 3.23 °C/W has been mounted. The
temperature was measured on the top of the packages of the power devices by means of a
thermocouple. A ∆T of 55 °C above ambient temperature has been measured.
14
Firmware flowchart
A simplified firmware flowchart is given in Figure 40.
40/44
AN2747
Firmware flowchart
Figure 40. Firmware flowchart
41/44
References
15
AN2747
References
1.
"Design of Fixed-Off-Time controlled PFC Preregulators with the L6562" (AN1792)
2.
"EVAL6562-375W, 375 W Fot-Controlled PFC pre-regulator with the L6562 (AN1895)
3.
"L6562-250W High performance TM PFC"
4.
"L6562 Transition-Mode PFC Controller" (datasheet)
5.
"STF12NM50 N-channel 500 V 0.29 Ω 11A MDMesh Power MOSFET" (datasheet)
6.
"STTH8R06DT Turbo 2 ultrafast high voltage rectifier" (datasheet)
7.
"L6385 HIGH-VOLTAGE HIGH AND LOW SIDE DRIVER" (datasheet)
8.
"STF20NM50 N-channel 500 V 0.29 Ω 11A MDMesh Power MOSFET" (datasheet)
9.
"STGP10NB60S N-channel 10 A 600 V PowerMesh IGBT" (datasheet)
10. "VIPer12 Low Power OFF-Line SMPS Primary Switcher" (datasheet)
11. "ST7FLITE39 8-bit MCU with single voltage Flash, data EEPROM, ADC, timers, SPI,
LINSCI" (datasheet)
12. "74AC00 QUAD 2-INPUT NAND GATE" (datasheet)
13. "LM119 High speed dual comparators" (datasheet)
14. "TS272I HIGH PERFORMANCE CMOS DUAL OPERATIONAL AMPLIFIERS"
(datasheet)
15. "LE50AB Very low drop voltage regulators with inhibit" (datasheet)
42/44
AN2747
16
Revision history
Revision history
Table 5.
Document revision history
Date
Revision
06-May-2008
1
Changes
Initial release
43/44
AN2747
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44/44