Meeting the Power Challenges of
General Lighting Applications
By Yin Wu, Senior Business Manager at Maxim Integrated,
Automotive Power Management Solutions, and Nazzareno
Rossetti, PhD EE, Maxim Integrated
February 2020
Abstract
The proliferation of LED drivers in general lighting
applications places new requirements on system
hardware, such as reduced component size to fit
additional electronics in the same space, improved
energy efficiency to perform within the same or lower
thermal budget, connected and flexible architectures
supporting multiple configurations, and accurate
control that preserves LED light characteristics.
In this white paper, we discuss the challenges for LED
drivers in different applications such as high-power
LED lighting, low/mid-power LED lighting, infrared
(IR) diodes for machine vision systems, and lowpower LED lighting.
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Introduction
IoT lighting
creates
smart and well-lit
applications that
LEDs have proliferated through countless
applications and across all markets over
the course of this decade (Figure 1). As
the LED market has reached economies
of scale, applications once dominated
by traditional incandescent lighting
are now utilizing many key features of
LED technology—high efficiency, high
brightness, precise control of light,
vast arrays of colors, unique shapes in
conjunction with new optics, and more.
LED illumination rise time is twice as fast
as incandescent sources and consumes
less power than its incandescent
counterpart, leading to substantial
advantages in energy consumption.
bring comfort and
simplicity to its
users
Figure 1. LED-Lighted Shenzhen
Improvements to LEDs and LED drivers
allow for applications that were not
traditionally possible and help adaptation
to new market needs. Industrial and stage
lighting provides high-contrast, bright,
and colorful systems for illuminating
the stage. Horticulture lighting utilizes
highly efficient designs at various color
spectrums to effectively grow highyielding plants. Machine vision systems
require sophisticated camera systems
that employ infrared or high-brightness
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LEDS (HB LEDs). IoT lighting creates
smart and well-lit applications that bring
comfort and simplicity to its users. These
are only a few applications that require
an LED paired with an LED driver. LED
drivers, the electronics that operate LEDs,
play an important part in preserving and
enhancing the inherent LED qualities of
clarity, speed, and efficiency.
Powering the LEDs
LEDs are used in many general lighting
applications and are available in diverse
configurations from a single LED to
a string or matrix of LEDs. HB LEDs
require constant current for optimal
performance. The current correlates with
junction temperature and, therefore, color.
Accordingly, HB LEDs must be driven
with current, not voltage. The LED power
source ranges from an AC-DC power
adapter for building illumination to a few
AAA batteries for closet lights and other
household devices.
The Challenges
The proliferation of LED modules in
general lighting places new requirements
on system hardware including: reduced
EMI, reduced component size to fit
additional electronics within the same
space, improved energy efficiency to
perform within the same or lower thermal
budget, supporting connected and
flexible architectures that enable multiple
configurations, as well as accurate control
to preserve LED light characteristics.
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In the following sections, we will cover the
following applications:
LED PANEL
MCU
1. High-power LED lighting
2. Low/mid-power LED lighting
3. Infrared (IR) diodes for vision
systems
4. Low-power LED lighting
The Solutions
High-Power LED Lighting
Buck-Boost Average Current Control
In line-operated applications, a switched
string of diodes can be fully engaged with
12 LED diodes (42V) or dimmed down to
a single LED diode (3.5V). The LED driver
may have an input voltage of 24V, while its
output voltage may go from 3.5V to 42V
and be above or below the input at any
given time.
Typical LED panels take power from a
separate AC/DC power-supply brick.
The power brick delivers a standard DC
voltage, for example 24V. Dedicated buckboost converters, working from this power
brick input, control the lamp’s intensity
and position. Each buck-boost converter
controls a single function such as daytime
or nighttime lights, light position, etc. The
matrix manager switches the string diodes
in or out, with each buck converter’s
output adjusted accordingly.
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BUCKBOOST
AC/DC
LED1
BUCKBOOST
SPI
LED1
LEDn
LEDk
SW1
12-SWITCH
MATRIX
MANAGER
SWk
Figure 2. LED Panel System from an AC/DC
Power-Supply Brick
Ideally, each string will have a customized
buck-boost solution, where the string
voltage is directly derived from the power
brick, with a step-down conversion when
possible (buck mode) and a step-up
conversion when necessary. Having as
low an input voltage as possible reduces
system switching losses and improves
efficiency.
Another concern is current and voltage
accuracy. The typical peak or valley
current-mode buck converter controls
the inductor peak current. However, the
diode string current is the average current
in the inductor. This peak-to-average
current error is eventually eliminated by
the outer voltage control loop but returns
during transient conditions. For example,
in Figure 2, the matrix manager may
instantly raise the number of powered-up
diodes from eight to twelve. The resulting
output-voltage step produces a current
and voltage fluctuation at the output of
the buck converter that takes tens of
microseconds to extinguish. A high-ratio
PWM dimming circuit will sample this
current for only a few initial microseconds
where the amplitude is dipping, resulting
in incorrect dimming brightness and color.
A string of diodes
can be fully
engaged with
12 LED diodes or
dimmed down to
a single LED
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A control loop that measures average
current, as opposed to peak current, would
naturally eliminate this problem.
Dimming is
a ubiquitous
function in many
applications and
an important
safety feature for
LED headlights
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Dimming is a ubiquitous function in many
applications and an important safety
feature for LED headlights. The human
eye can barely detect light dimming from
100% to 50%. Dimming must go down
to 1% or less to be clearly discernable.
With this in mind, it is not surprising that
dimming is specified by a ratio of 1000:1
or higher. Given that the human eye, under
proper conditions, can sense a single
photon, there is practically no limit to this
function.
Since current must be kept constant
to preserve color, the best dimming
strategy for LEDs is PWM (pulse-width
modulation), where the light intensity is
modulated by time-slicing the current
rather than by changing the amplitude.
The PWM frequency must be kept above
200Hz to prevent the human eye from
perceiving the LED light as flickering.
With PWM dimming, the limit to the
minimum LED “on/off” time is the time it
takes to ramp up/down the current in the
switching regulator inductor. This may add
up to tens of microseconds of response
time, which is too slow for applications
that require fast, complex dimming
patterns. Dimming in this case can only be
performed by individually shunting each
LED in a string by means of dedicated
MOSFET switches (SW1-K in Figure 2).
The challenge for the current control loop
is to be fast enough to quickly recover
from the output-voltage transient due to
switching in and out of the diodes.
An ideal solution should meet the
requirements of smooth buck-boost
operation and fast transient response. The
LED controller shown in Figure 3 enables
such a solution.
RIN
INPUT
VOUT
COUT
CIN
INP
INPUT
AND BIAS
DH1
PWM AND
ANALOG
DIMMING
DL1
RCOMP
L1
N3
DH2
LX2
N2 N4
DL2
VOUT
CSP
MAX25600
RSENSE
ISP
RCS_LED
CSN
DH2
ISP, ISN
CCOMP
N1
LX1
RT, SS
FLT
IOUTV
FB
INN
ISN
LX2
COMP
P1
DL2
DIMOUT
Figure 3. LED Controller with Smooth Buck-Boost
Operation and Fast Transient Response
Typically, the diode string is attached
directly to VOUT. The IC integrates a highside p-channel dimming MOSFET driver
(DIMOUT) for applications that require
a current source with PWM dimming
capability as shown in Figure 3.
High-Power Buck LED Controller
Buck converters (a.k.a. direct energy
devices), thanks to their uninterrupted
current flow from the inductor to the
output, are inherently more efficient
than boost and buck-boost converters.
Naturally, the use of a buck converter
implies that the output voltage is always
lower than the input voltage. Whenever
possible, based on the characteristics of
the application, buck converters result in
more efficient lighting fixtures.
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An ideal solution should meet the
requirements of a wide input voltage
range, fast transient response, high and
well-controlled switching frequency,
all while enabling high efficiency with
synchronous rectification. The LED
controller in Figure 4 enables such a
solution.
INPUT
CIN
Reconfiguration
CVCC
D1
R1
for fast time-toBST
VCC
IN
DH
Q1
market points to
CBST
an ability to
MAX20078
L1
TON
communicate
LX
C1
COUT
DL
PWM
Q2
R2
DIM
LED CURRENT CONTROL
FAULT FLAG
REFI
with the LED
controller IC
CSP
RCS
FLT
CURRENT MONITOR
LED1
R3
LEDn
CSN
IOUTV
PGND
AGND
OUT
Figure 4. Synchronous High-Power Buck LED Driver
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Dual LED Buck Controllers
The space challenge clearly points to more
integration of the LED controller building
blocks, while the reconfiguration for fast
time-to-market points to an ability to
communicate with the LED controller IC.
The synchronous, all n-channel buck
LED controller with SPI interface shown
in Figure 5, integrates two channels in a
single IC, which reduces the BOM and
Reconfiguration
VIN
for fast time-tomarket points to
T1
an ability to
communicate
with the LED
solution footprint. Two out-of-phase
channels smooth out the input current,
spreading out its energy, resulting in lower
RMS current and lower EMI emissions.
With a lower RMS current, smaller and
less expensive input capacitors can be
used. A high, well-controlled switching
frequency, outside the AM frequency
band, reduces radio frequency interference
and meets EMI standards.
VOUT,
IOUT
LED1
FB
T’1
L
MAX20096
LED
CONTROL
T2
COUT
controller IC
LEDn
FB’
L’
RSENSE
FB
V’OUT,
I’ OUT
LED’1
T’2
C’OUT
FB’
R’SENSE
LED’n
Figure 5. Synchronous High-Power Dual-Buck LED Controller
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Fast transient response prevents output
voltage and current fluctuations, which
is consequent to instantaneous variation
of the diode string length in high-ratio
dimming applications. The device is ideal
for matrix lighting and LED driver module
(LDM) platforms.
The utilization of an advanced silicon
process allows the entire dual controller
function to be housed in a small package.
Synchronous rectification eliminates
Schottky diodes and greatly reduces
power losses in high-current applications,
while allowing the use of smaller discrete
MOSFETs.
buck-derived solution that meets
integration, efficiency, and flexibility
challenges.
Closet lights, shed lights, and other
home applications require one or two
LED diodes for operation and are often
battery operated. For a typical LED diode
that develops 3.5V at 1A, this type of
application can be well served by a simple
buck converter powered by a 9V battery.
In Figure 6, the buck-converter inductor
current builds up when N1 is ‘on’ and is
maintained ‘on’ through N2 when N1 is
‘off.’ Synchronous rectification accounts
for the high efficiency.
Low-/Mid-Power Lighting
VIN
solution meets the
N1
integration,
Flexible LED Drivers
LEDs have penetrated many lighting
applications thanks to their versatility and
efficiency. As an example, portable LED
applications must be small and efficient
enough to fit in the existing space without
overheating. With so many different
functions, one might expect a lighting
manufacturer to be resigned to keeping a
large quantity of different LED drivers in
stock. This can have severe implications
in terms of reducing a manufacturer’s
purchasing power due to low volume orders,
longer design cycles, and delayed time to
market.
L
VBATT
CIN
A buck-derived
VOUT
LED1
N2
COUT
LEDn
efficiency, and
flexibility
challenges
Figure 6. Buck Converter Operation
Brighter home applications may require
three or four LED lights to operate. Here,
the voltage ranges from 10.5V to 14V. With
our 9V battery, the best configuration for
this type of application is a buck-boost
converter. One example of a buck-derived
Is it possible to have an efficient, highly
integrated LED driver that is flexible enough buck-boost implementation is shown in
Figure 7. Notice how the output voltage
to cover the majority of applications? This
case study reviews the power requirements is always below ground. The inductor
of three classes of LED lighting applications builds up current when N1 is ‘on’ and is
maintained through N2 when N1 is ‘off.’
and highlights the optimal LED driver
topology for each case (buck, boost, buckboost). It then introduces an innovative
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The voltage across the inductor inverts
at each transition, independently of
the number of diodes. Accordingly,
this configuration can operate with any
number of diodes on the output, and a
string voltage drop that adds up to a value
that is above or below the input voltage
(buck-boost operation).
it makes no
is voltagereferenced
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L
LED1
N2
VOUT
N2
COUT
LEDn
difference where
the LED string
CIN
CIN
LED1
applications,
VBATT
LEDn
VBATT
L
In portable LED
N1
COUT
VIN
N1
VIN
VOUT
Figure 7. Buck-Derived Buck-Boost Operation
The brightest applications may require
long strings of diodes. In this case, the best
configuration is the boost converter. In the
buck-derived boost converter of Figure 8,
the output voltage floats below the input
voltage. The inductor builds up current
when N1 is ‘on’ and is mantained through
N2 when N1 is ‘off.’ For the voltage across
the inductor to invert at each transition,
the number of diodes must be high enough
so that the output voltage is negative with
respect to ground. For this reason, the
configuration can only operate with a high
number of diodes in the string, in this case,
8 (28V string).
Figure 8. Buck-Derived Boost Operation
Buck, boost, and buck-boost canonical
implementations can be very different and
are very difficult to reconcile in a single
IC. However, in portable LED applications,
it makes no difference where the string
is voltage-referenced. This opens up an
opportunity to adopt a buck-derived
topology for both the buck-boost and
boost converter. In the above three
examples, the cathode of the LED’s bottom
diode is opportunistically referenced to
ground (buck) or VOUT (buck-boost and
boost) while the anode of the LED’s top
diode is referenced to VOUT (buck) or
ground (buck-boost and boost). Indeed,
it is possible in this application to have
a single flexible topology for all cases,
with minor adjustments of the IC and the
application configuration.
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The IC in Figure 9 is a fully synchronous
LED driver that provides constant output
current to drive high-power LEDs. The IC
integrates two 60mΩ power MOSFETs for
synchronous operation, high efficiency,
and a minimum number of external
components. Flexible configuration
supports buck, inverting buck-boost, and
boost conversion. The devices can operate
in two modes. For buck mode, connect a
2.49kΩ resistor from VCC to the PWMFRQ
pin. For buck-boost or boost mode,
connect a 17.8kΩ resistor from VCC to the
PWMFRQ pin.
Infrared Diode for Vision Systems
Machine vision is an important tool for
Industry 4.0. Infrared (IR) cameras utilize
an IR LED in combination with a photo
sensor and are critical components of
machine vision, which is used to measure
and count products, calculate product
weight or volume, and inspect goods at
top speed with respect to predefined
characteristics. IR machine vision lighting
enables industrial vision systems to
recognize objects and their condition
under difficult lighting conditions such as
reflective surfaces that produce high levels
of visible-spectrum noise, high or low
levels of illumination, or target areas with
variable light intensities.
Machine vision is
an important tool
for Industry 4.0
VIN+
CIN
VIN-
CIN2
INP
BST
INN
LX
LX
IC-GND
CVEE
PWM or
ANALOG
DIMMING
OUT
CBST
L
ROUT1
LED1
COUT
PWMDIM
MAX25610A
OPEN-DRAIN
FAULT
CPWMFRQ
PWMFRQ
RREFI
ROUT2
LEDn
PGND
100kΩ
RPWMFRQ
CVCC
BATTERY GND
VIN-
VCC
COMP
CCOMP
REFI
AGND
IC-GND
DOMAIN
RCOMP
Figure 9. Integrated, Flexible Converter in Buck-Boost Mode
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All these functions and their associated
electronics must fit seamlessly inside
a robot, creating the need for flexible,
small, and efficient solutions. They must
also cope with harsh industrial electrical
environments
The LED driver
controls the IR
light intensity and
Some key advantages of IR light are its
invisibility to the human eye and its ability
to work day and night. Figure 10 shows
the main elements of an infrared camera.
The IR LED illuminates the target. The
reflected light is collected by the image
sensor (CCD or CMOS photo diode) and
processed by the vision processor to
determine the response to the situation at
hand.
LENS
IMAGE
SENSOR
strobes it at the
VISION
PROCESSOR
The LED driver controls the IR light
intensity and strobes it at the right
frequency and duty cycle. Ideally, it must
work off a low-voltage DC rail and cope
with a harsh industrial environment.
The industrial environment is subject to
electromagnetic interference (EMI) due
to both external and internal sources.
The “arc and spark” noise that comes
from soldering components, motors,
and similar pulse-type systems affects
the supply voltage rails by producing
disruptive undervoltages or overvoltages.
The IR LED buck converter, despite its fast
switching waveforms, should mitigate any
contribution to this noisy environment.
As an example, the synchronous buck LED
driver in Figure 11 is an ideal solution.
right frequency
and duty cycle
LED
DRIVER
ILLUMINATION
IR-LED
Figure 10. IR LED Camera for Vision Systems
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INPUT
C1
1µF
FAULT FLAG
C2
1µF
IN
BST
MAX20050 LX
C3
0.1µF
L1
R CS
LX
FLT
VCC
CS+
CS-
R2
AGND
REFI
PGND
R1
PWM
COUT
EP
PWM
In batteryFigure 11. IR LED Driver Integrated, Synchronous Solution
operated
applications, the
Low-Power LED Lighting
Small Lights
Low-power applications can be powered
by the AC-line or by batteries. In batteryoperated applications, like closet lighting
and other household applications, the
power source can be a few AAA batteries,
with wide input voltage swings.
These home and building applications
require less power and are handled by
simple single-function ICs. Here, the
MAX20090 can be utilized as a boost
LED controller for long strings that require
voltages above the nominal power brick
or battery voltage, or as a front-end boost
voltage regulator. The buck converter in
Figure 11 can drive short strings of diodes
that are connected to the battery or to a
low-voltage power brick. Alternatively, it
can drive long strings of diodes with the
help of a front-end boost converter.
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For noise-sensitive applications, a linear
LED driver can be utilized. The threechannel LED driver in Figure 12 operates
from a 5.5V to 40V input voltage range
and delivers up to 100mA per channel
to one or more strings of HB LEDs. Each
channel’s current is programmable using
an external current-sense resistor in
series with the LEDs. Three DIM inputs
allow a wide range of independent pulsed
dimming in addition to providing the on
and off control of the outputs. Waveshaping circuitry reduces EMI while
providing fast turn-on and turn-off times.
power source can
be a few AAA
batteries.
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VIN
MAX16823
CIN
IN
OUT1
IN
OUT2
IN
OUT3
DIM1
DIM2
DIM3
REG
RLEDGOOD
CS1
LEDGOOD
CLGC
LGC
CS2
REG
CS3
GND
CREG
CS1
CS2
CS3
Figure 12. Linear Driver for Low Noise
Conclusion
The proliferation of LED modules in general lighting applications places new
requirements on system hardware including: reduced component size to fit additional
electronics in the same space, improved energy efficiency to perform within the same
or lower thermal budget, connected and flexible architectures that support multiple
configurations, and accurate control to preserve LED light characteristics.
In this white paper, we discussed the challenges in high-power and low/mid-power
lighting, IR cameras used in vision systems, and low-power lighting. In each case, we
proposed the best solution based on the application at hand.
Related Resources
Design Guides
Led Drivers for General Lighting
Led Drivers for Automotive Applications
Learn more
For more information, visit:
www.maximintegrated.com/led-drivers
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