The Top Five Global
Lighting Technologies
By Tom Ribarich, Director, Lighting IC Design Center,
International Rectifier, El Segundo, Calif.
The varying electrical characteristics of different
lighting technologies dictate a range of power
control solutions.
oday’s lighting applications include
residential lighting, office interior
lighting, retail and display lighting,
outdoor lighting, mood lighting, and
emergency lighting. These applications
have different lighting needs and are satisfied by specific lighting technologies. The
top five global lighting technologies (excluding incandescent) include compact
fluorescent, linear fluorescent, halogen,
high-intensity discharge and light-emitting
diodes (see the table).
Residential and hotel applications typically use compact fluorescent lamps (CFLs)
to replace incandescent lamps, reduce energy costs and for
easy insertion into existing ceiling or table fixtures. Office
interior lighting applications use tubular fluorescent lamps
because of their large area of light coverage. Halogen light-
ing is the preferred technology for display and retail lighting due to the color and spotlight produced by these lamps.
High-intensity discharge (HID) lamps deliver a highbrightness output and typically are used for outdoor and
street lighting applications.
T
The top five global lighting technologies include
compact fluorescent, linear fluorescent, halogen,
high-intensity discharge and light-emitting diodes.
Finally, light-emitting diodes (LEDs) are used for mood
and emergency lighting applications because of their colormixing capabilities, low-power consumption, low maintenance and ultra-long lifetime. These lighting technologies
have different electrical characteristics, and each technology requires a unique control solution.
Compact Fluorescent
A compact fluorescent lamp consists of a small-diameter fluorescent lamp that has been formed into a compact
shape, a polycarbonate mid-section that contains the control circuitry for powering the lamp and an Edison screw
base for mounting the lamp into a standard incandescent
lamp socket.
The fluorescent lamp consists of a glass tube filled with
Argon gas and a small amount of mercury. Filaments are
located at each end of the tube and usually are coated with
Boron to help emit electrons. As electrons flow across the
tube from one filament to the other, they collide with mercury atoms. The excited mercury atoms give off UV light,
which is then converted into visible light as it passes through
the phosphor coating on the inside of the tube. The higher
the number of collisions, the higher the light output from
the lamp. The spiral shaped CFL has proved to be the most
Fig. 1. Fluorescent lamp operating points.
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LIGHTING TECHNOLOGIES
popular because the light produced
in the center of the lamp can escape
to the outside, giving a higher light
output than other shapes.
Fluorescent lamps have three
operating points—preheat, ignition
and run—that must be fulfilled in
a proper sequence. To accomplish
this, a resonant mode circuit is
used. During preheat and ignition,
the circuit has a high-Q and is
under-damped. The circuit starts at
the preheat frequency for a fixed
time to preheat the lamp filaments
and then decreases the operating
frequency toward resonance to Fig. 2. CFL control circuit.
increase the output voltage to ignite the lamp. After the lamp ignites, the circuit becomes
a low-Q, over-damped circuit and the frequency is decreased further until the rated lamp power is reached
(Fig. 1).
The running working voltage of a fluorescent lamp
ranges from about 50 Vac to 150 Vac, depending on the
lamp type and power rating; the operating frequency is
typically around 50 kHz. The control circuit first rectifies
and smoothes the ac mains voltage to produce a dc bus
voltage with an amplitude of several hundreds of volts
(Fig. 2). The circuit then generates a high-frequency squarewave using a high-voltage control IC and two MOSFETs
connected in a totem-pole half-bridge configuration. The
high-voltage square-wave drives the resonant output stage
across the lamp and sweeps the frequency to fulfill the
lamp operating points.
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LIGHTING TECHNOLOGIES
Tubular Fluorescent
EMI Filter
Rectifier
PFC
Output Stage
Half- Bridge
Lamp
IR2166
Tubular fluorescent
lamps have the same elec+
Line
trical characteristics as
compact fluorescents, but
the control circuit must fulfill additional performance
PFC Control
and protection requirements. The block diagram
of a tubular fluorescent balDriver
UVLO
Control
last circuit depicted in Fig.
Lamp Fault
3 includes an EMI filter to
block ballast generated
noise, a bridge rectifier, a
Controller
power factor correction
(PFC) circuit for sinusoidal Fig. 3. Tubular fluorescent ballast block diagram.
input current, half-bridge
MOSFETs with driver and timing for
high-frequency operation, and final
resonant output stage for fulfilling the
lamp operating points. In addition,
the control circuit must protect
against various lamp and line fault
conditions. The ballast must survive
many years of transient voltage spikes
or brownouts at the mains input, as
well as lamp failures and re-lamping
at the output.
The primary difference between
the tubular fluorescent ballast and the
CFL ballast is the addition of the PFC
circuit. PFC is mandatory in Europe
Fig. 4. Halogen converter control circuit.
for power levels above 25 W and the
boost-type topology has proven to be
fed with a constant voltage so that the
input voltage, but it also regulates the
the most popular solution. Not only
light output from the lamp stays condc bus voltage at a constant level.
does the PFC provide a sinusoidal instant over a wide ac mains input voltThis approach means the halfput current that is in phase with the
age range. This allows for the ballast
bridge and resonant output stage is
Boost PFC
Buck
Full Bridge
6
1
5
7
8
RECT (+)
4
3
2
1
4
Lamp
7
6
5
Ignitor
2
3
4
8
IR2153
3
1
8
IR2153
IR2117
2
7
6
5
RECT (-)
+15V
Control
Circuitry
Fig. 5. HID ballast block diagram.
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LIGHTING TECHNOLOGIES
to work across a universal input voltage range, and it becomes easy to
adapt the output stage to different
lamp types or lamp configurations
while maintaining the same design
platform.
Halogen
Halogen lamps use a tungsten filament that is encased inside a small
quartz envelope. Similar to an incandescent lamp, the electrical current
causes the tungsten filament to heat
up to temperatures above 2500°C and
get “white hot” and produce visible
light. Halogen and incandescent lighting technologies use heat to excite atoms. With a halogen lamp, the envelope is much closer to the filament.
Thus, to prevent it from melting, the
envelope is made from quartz. The gas
inside the envelope consists of a gas
from the halogen group.
These gases have an interesting
property in that they combine with
tungsten vapor. If the temperature is
high enough, the halogen gas will
combine with tungsten atoms as they
evaporate and redeposit them on the
filament. This recycling process lets
the filament last much longer than incandescent. In addition, because the
filament is running hotter, more light
per unit energy is achieved. This is
why halogen lamps are ideal for intense “spot” lighting applications.
The halogen lamp has different
electrical characteristics than fluorescent. There is no high-voltage ignition
required to start the lamp, and the
working lamp voltage is limited to between 11.2 V and 11.7 V. Anything
below this range will give a reduced
light output and anything above will
cause premature aging. Halogen control circuits are known as “halogen
converters” or “electronic transformers.” They step the mains input voltage down to the required working
voltage range, provide galvanic isolation and allow for the lamp to be
dimmed with a standard phase-cut
triac wall dimmer.
The applications for these lamps
include long exposed tracks to which
the lamps are connected. These tracks
www.powerelectronics.com
Technology
Application
Reason
Compact Fluorescent
(CFL)
Residential and Hotel
Lighting
Incandescent
replacement
Tubular Fluorescent
Industrial Office Lighting
Large area lighting
Halogen
Retail/Display Lighting
Spotlighting, highlighting
High-Intensity Discharge
(HID)
Outdoor Lighting
High brightness
Light-emitting Diode
(LED)
Mood/Emergency Lighting
Color mixing,
long lifetime
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Power Electronics Technology October 2004
LIGHTING
are continuously being touched directly by the user, and lamps are being connected and moved depending
on the desired lighting effect. To avoid
electrical shock to the user, these
tracks must be galvanically isolated
from the mains. The control circuit
also must protect against open-circuit
(no lamps connected), overload (too
many lamps connected) and shortcircuit (tracks shorted together) fault
conditions.
To satisfy these requirements, a
typical halogen converter circuit includes EMI filtering, rectification, two
half-bridge MOSFETs, a transformer
to step the voltage down, and a control IC (Fig. 4). This chip drives the
half-bridge at high frequency, regulates the lamp output voltage, provides
soft-start and dimming, protects
against all fault conditions and restarts
the lamp when the fault is removed.
High-Intensity Discharge
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HID lamps are available in the
form of mercury or sodium vapor and
typically are used as street lamps and
outdoor lighting for stadiums. These
lamps are popular because they are
efficient and have a high-brightness
output. In the case of sodium vapor,
they are twice as efficient as normal
fluorescent bulbs.
Mercury and sodium vapor lamps
produce light using a technique similar to that used in fluorescent lamps,
where a low-pressure mercury vapor
produces lots of ultraviolet light that
excites a phosphor coating on the
tube. In the case of mercury vapor
lamps, it is a high-pressure gas, the
distance between the electrodes is
short and the light is produced directly without the need for the
phosphor.
HID lamps require a high ignition
voltage (3 kV to 4 kV) and even higher
(>20 kV) if the lamp is hot. In addition, they have working voltages of
100 V to 200 V. HID lamps also are
typically operated at low frequency
(100 Hz to 200 Hz) to avoid damage
from acoustic resonance. The HID
ballast block diagram shown in Fig. 5
includes an EMI filter, a bridge rectiwww.powerelectronics.com
LIGHTING TECHNOLOGIES
fier, a boost converter for PFC, a buck
converter to control the lamp current,
an ignition circuit, a full-bridge for
driving the lamp at low-frequency,
and various high-voltage driver ICs
and circuitry for controlling the different blocks.
Light-Emitting Diode
The LED is an emerging lighting
technology due to recent breakthroughs in high-brightness LEDs.
LEDs have always been attractive light
sources because of their ultra-long
lifetime and low-power consumption.
However, they were limited to only a
few colors and low brightness levels.
High-brightness LEDs now are available in many colors and have enabled
this technology to penetrate into certain mainstream general-purpose
lighting applications, including emergency lighting, traffic lights, display
and mood lighting.
LEDs work on a completely differ-
Fig. 6. Buck converter LED control circuit.
ent principle than ordinary lamps. As
in silicon and germanium-based
semiconductors, the compound semiconductor materials used to build
LEDs exhibit the band-gap property
whereby individual electrons move in
jumps that involve much higher energy levels than those associated with
electron flow in conductors. In one
particular family of compound semi-
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conductor materials based on the rare
metal gallium, the band-gap is so wide
that appreciable energy is needed to
make electrons jump.
When each electron recombines
with an atom, it emits a particle of
light called a photon. These jumps
take place across the junction between
the n- and p-type regions of the semiconductor crystal. Semiconductor
materials based on gallium have the
useful property of being transparent,
allowing the light generated to escape
from the junction.
LEDs are much simpler to control
than other lamp types but still have
their own set of requirements and
challenges. They do not need to be ignited or preheated, but the current
should be constant and matched in
each LED. Furthermore, depending
on the application, the electrical connection to the LEDs may or may not
need to be galvanically isolated. A
typical nonisolated off-line circuit
used is a high-voltage buck converter
for controlling the current through a
string of LEDs connected in series
(Fig. 6).
The buck operating frequency is
maximized to reduce the size of the
inductor. Each LED has a given voltage drop; thus, the number of LEDs
that can be connected depends on the
available input voltage to the circuit.
The source of the MOSFET is at the
high-voltage input each time the
MOSFET is turned on, requiring a
high-voltage gate driver IC.
The control circuitry then senses
the LED current through a currentsensing resistor and controls the buck
on- and off-time to keep the current
constant. Finally, a shutdown input is
used to dim the LEDs using a low-frequency PWM on/off dimming control signal.
Ballast Design Software
Available from International Rectifier is a software program to help
designers quickly begin new ballast
designs. The program, Ballast Designer V4.0, offers a friendly graphic
interface that allows users to select
from various control ICs, lamp types,
and input and output configurations.
When all of the parameters are selected, the user can then generate a
schematic, bill of materials and inductor specifications so they can get
started on their prototyping. An advanced display page also is available
for closer examination of the calculations, operating points and timedomain waveforms.
PETech
To download this software and for
more information on the control ICs
mentioned in this article, visit
www.irf.com.
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For more information on this article,
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