designfeature
Tom Ribarich
Director, Lighting Systems, International Rectifier
How To Control and Reap
the Benefits of HID Lamps
Electronic HID (high intensity
discharge lamp) ballasts: how
they work, how to control
them, and develop an electronic ballast solution for outdoor lighting applications.
Bulb Envelope
Mercury and
Metal Halide
Atoms
Arc
Electrode
Arc Tube
H
brightness metal halide lamps typically have an efficacy of greater than 100 lumens/watt and have a lifetime of 20,000 hours.
HID lamps produce light using a technique similar to that used
in fluorescent lamps where mercury atoms are excited by an
electrical current resulting in the production of ultraviolet (UV)
light. The UV light is then converted into visible light through a
phosphor coating on the inside of the tube. In the case of HID
lamps, they operate at a high-temperature and high-pressure, the arc length is very
short, and visible light is produced directly without the need for a phosphor.
Metal halide lamps (Figure 1) comprise an arc tube surrounded by an outer bulb envelope. The arc tube is made
of quartz or ceramic glass, has tungsten electrodes located
at each end, and contains a mixture of argon, mercury and
metal halide salts. Metal halide is added to the lamp to
increase lumens and improve the light color.
The lamp is started by applying a high voltage pulse
across the tube to ionize the argon gas. Once the gas is
fully ionized, a sustained arc extends from one electrode
to another and current (supplied by a ballast) flows across
the tube. As the pressure and temperature inside the tube
increase, the materials within the arc tube vaporize and
light is emitted in the form of visible light and UV radiation. The outer bulb envelope provides a stable thermal
environment for the arc tube, prevents oxidation of the arc
tube, and reduces the amount of UV radiation emitted by
the lamp.
HID Lamp Characteristics
Fig. 1. HID lamps comrpise an arc tube surrounded by an outer bulb envelope.
V, I
07_Ribarich_F1
Warm-up
Running
VLAMP
PLAMP
ILAMP
Ignition
Current
Limitation
Constant Power
36 Power Electronics Technology | July 2010
07_Ribarich_F2
HID lamps require a high voltage for ignition (3 to 4KV
typical, >20KV if the lamp is hot), current limitation during warm-up, and a constant power during running. It is
important to have a tight regulation of lamp power to
minimize lamp-to-lamp color and brightness variations.
Also, HID lamps are driven with a low-frequency AC
voltage (<200Hz typical) to avoid mercury migration and
to prevent damage of the lamp due to acoustic resonance.
A typical metal halide 250W HID lamp has the following
characteristics:
• Nominal Wattage (W): 250
t
Fig. 2. Typical start-up profile for HID lamp ignition, warm-up and running
modes.
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cONTROLLINGHIDLamps
Full-Bridge Stage
Buck Stage
Fig. 3 HID lamp ballast circuit employs a buck
stage to control the lamp current, followed by a
full-bridge output stage for ac lamp operation.
MBUCK
DC Bus (+)
LBUCK
Gate
Drive
TIGN
Lamp
• Nominal Voltage (Vrms): 100
Gate
Gate
Drive
Drive
• Nominal Current (Arms): 2.5
DIGN
DC Bus (–)
RIGN
• Warm-up Time (min): 2.0
Current
Zero Crossing
• Ignition Voltage (Vpk): 4000
MIGN
VLAMP
CIGN
Detection
Figure 2 shows the typical start-up
Lamp Power
Off-Time
Feedback On-Time
profile for HID lamps. Before igniControl
Control
tion, the lamp is open circuit. After
Full-Bridge
Ignition
Control
Control
the lamp ignites, the lamp voltage
ILAMP
drops quickly from the open-circuit
voltage to a very low value (20V
typical) due to the low resistance of the lamp. This causes
and power increase. Eventually, the lamp voltage reaches
the lamp current to increase to a very high value and
its nominal value (100V typical) and the power is regushould therefore be limited to a safe maximum level. As
lated to the correct level.
the lamp warms up, the current decreases as the voltage
To satisfy the lamp requirements and different oper-
07_Ribarich_F3
Buck Circuit
VBUS+
400 V dc
MBUCK
IRF P 22 N60 K
Heatsink
RBCS
0.16 R/5W/1%
RBUCK1
RBB 2
68k
0.25 W
RBB 3
68k
0.25 W
DBUCK1
1N4148
RBB 3
68k 0.25 W
DVBB 1 600 V 1A
+
14 V dc
–
CBUS
82 µF
450 V
LBUCK
0.23 mH/10A pk/E F 42
DBUCK
ST T H 12 R 06
Heatsink
RCCS 1
1k
CCS 1
470 pF
DVBB 2
15 V/0.5 W
CBUCK
3.3 µF/400 V
CS
1
VB1
28
BUCK
2
HO1
27
VSB
3
VS1
26
CVBB
2.2 µF VBB
4
RVBB 1 10 R
VCC
LO1
25
5
LO2
24
COM
6
VB2
23
ZX
7
HO2
IRS2573D 22
TOFF
8
VS2
21
CICOMP 3.3 nF ICOMP
9
IGN
20
CPCOMP 3.3 nF PCOMP
10
OV
19
CVCC 1
0.1 µF
CVCC2
10 µF
Full-Bridge Circuit
RZX CRZX
33 k 10 pF
CT OFF 3.3 nF
RIREF 20k
IREF
11
17
TIGN
13
16
CTCLK 0.18 µF TCLK
14
15
CTIGN 1 µF
RLO1
22R
MHS2
IRGB
15 B 60 K D
Heatsink
LIGN
1 mH/EF 25
VOGT IC
0806203101
250 W Lamp
MLS1
IRGB
15 B 60 K D
Heatsink
MLS2
IRGB
15 B 60 K D
Heatsink
RHO2
22R
RVS 2
180k
1%
RLO2
22R
CVB2
2.2 µF
50 V
DIGN
K 1V 26
COV 0.1 µF
ROV 120k
ISENSE
VSENSE
N/C
COUT
1 nF/630 V
MHS1
IRGB
15 B 60 K D
Heatsink
RHO1
22R
OC ROC 10k
18
CT
12
CT 0.068 µF
CVB1
2.2µF
50 V
RVS 1
180k
1%
COC RISENSE
0.1 µF 1k
CISENSE
0.1 µF
CVS
10 nF
RIGN 3
22R
RIGN 1
22R
RIGN 2
18 K/3W
M1
IRLL 3303
RCS
0.12R
5W 1%
DVS 1
36 V
0.5 W
MIGN
IRGB
10 B 60 K D
Heatsink
RVS 3
100k
1%
CIGN
0.1 µF
630 V
RVS 4
7.5k
1%
VBUS–
Programming Inputs
Voltage/Current Sensing
Ignition Circuit
Fig. 4 250W HID ballast circuit uses a complete buck and full-bridge control circuit designed around the IRS2573D HID Control IC.
07_Ribarich_F4
www.powerelectronics.com July 2010 | Power Electronics Technology
37
cONTROLLINGHIDLamps
(A)
(B)
Figure 5 HID ballast waveforms
A) During lamp warm-up: buck switching node voltage (upper trace); buck current
(lower trace).
B) During normal lamp running: buck switching node voltage (upper trace; buck
current (lower trace).
C) During normal lamp running: half-bridge output voltage (upper and middle
traces); ac lamp current (lower trace).
ating modes, an electronic ballast circuit is needed that
ignites the lamp, controls lamp power, and produces an
AC lamp voltage.
HID Ballasts
The standard circuit for controlling HID lamps includes
(Figure 3) a buck stage for controlling the lamp current,
followed by a full-bridge output stage for ac operation
of the lamp. The output stage also includes an ignition
circuit for striking the lamp. A control circuit or IC is necessary to control the buck and full-bridge stages and properly managing the different lamp modes. The buck circuit
is fed by a constant dc bus voltage (400Vdc, typical) that
can be supplied by a commonly used active power factor
correction circuit.
The buck stage is the main control circuit of the ballast
and is used to control the lamp current and power. The
buck stage steps the dc bus voltage down to the lower
lamp voltage at the full-bridge stage. The lamp voltage and
current are measured and multiplied together to produce a
lamp power measurement. The lamp power measurement
is then fed back to control the on-time of th buck switch
(MBUCK). The buck off-time each switching e cycle is
determined by the zero-crossing of the buck inductor
current and is sensed using a secondary winding from the
buck inductor (LBUCK).
The full-bridge stage is necessary to produce an ac
lamp current and voltage during running. The full-bridge
38 Power Electronics Technology | July 2010
(C)
typically operates at 200Hz with a 50% duty-cycle. The
full-bridge also contains a pulse transformer circuit for
producing 4KV pulses across the lamp necessary for ignition. The ignition circuit includes a diac circuit to produce
the required ignition pulses. The ignition circuit is activated by turning on MIGN, causing the lower leg of the
diac, DIGN, to discharge with a time constant determined
by RIGN and CIGN. When the voltage across the diac
reaches the diac threshold, the diac then diac breaks down
and a voltage pulse is produced across the primary winding of the ignition transformer, TIGN. This produces 4KV
pulses across the secondary winding of TIGN and across
the lamp for ignition.
The complete buck and full-bridge control circuit
schematic is shown in Figure 4. The circuit is designed
around the IRS2573D HID Control IC from International
Rectifier. The IRS2573D includes control for the buck
stage, the full-bridge, lamp current and voltage sensing,
and feedback loops for controlling lamp current and lamp
power. The IC includes an integrated 600V high-side
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cONTROLLINGHIDLamps
This solution also
allows for scalability
of design so that the
same basic circuit can
be used as a platform
to realize a family of
electronic ballasts for
many lamp types and
power levels.
driver for the buck gate drive (BUCK
pin) with cycle-by-cycle over-current
protection (CS pin). The on-time of
the buck switch is controlled by the
lamp power control loop (PCOMP
pin) or lamp current limitation loop
(ICOMP pin). The off-time of the
buck switch is controlled by the
inductor current zero-crossing detection input (ZX pin) during criticalconduction mode, or by the off-time
timing input (TOFF pin) for continuous-conduction mode. The IC
also includes a fully-integrated 600V
high- and low-side full-bridge driver.
The operating frequency of the fullbridge is controlled with an external
timing pin (CT pin). The IC provides
lamp power control by sensing the
lamp voltage and current (VSENSE
and ISENSE pins) and then multiplying them together internally to generate the lamp power measurement.
The ignition control is performed
using an ignition timing output (IGN
pin) that drives an external ignition
MOSFET (MIGN) on and off to
enable the ignition circuit of the lamp
(DIGN, CIGN, TIGN). The ignition timer is programmed externally
(TIGN pin) to set the ignition circuit
on and off times. Finally, the IC
includes a programmable fault timer
(TCLK pin) for programming the
allowable fault duration times before
shutting the IC off safely when various fault conditions occur. Such fault
conditions include failure of the lamp
www.powerelectronics.com to ignite, failure of the lamp to warmup, lamp end-of-life, arc instabilities,
and open/short circuit of the output.
Waveforms
Figure 5 illustrates the experimental
results. Figure 5A shows the buck
switching node voltage (upper trace)
and buck current (lower trace) during
lamp warm-up. Figure 5B shows the
buck switching node voltage (upper
trace) and buck current during steadystate running conditions. The buck is
working in critical-conduction mode
during steady state running conditions and the on-time is controlled
by the constant power feedback loop.
Figure 5C shows each half-bridge
output voltage (upper and middle
traces) and ac lamp current (lower
trace) during normal lamp running
conditions.
The design presented here is a
standard approach that utilizes a
highly-integrated control IC, the
IRS2573D, to greatly simplify the
design of the circuit. This solution
also allows for scalability of design
so that the same basic circuit can be
used as a platform to realize a family of electronic ballasts for many
lamp types and power levels. The
new IRS2573D control IC contains
the complete HID system-in-a-chip,
including lamp control, lamp ignition, and all fault protection circuitry.
This control IC makes the lighting
solution very reliable and ideal for
designers facing time-to-market pressures to introduce their products into
the marketplace.
High intensity discharge lighting is
a growing market with many applications. Outdoor lighting is especially
attractive for high-intensity lamps,
due to the long life-time and highbrightness these lamps deliver and
the enormous energy saving benefits
that electronic ballasts offer. The
lamp requirements are critical and
the ballast requirements are challenging, making the design of the electronic ballast a difficult task.
July 2010 | Power Electronics Technology
39