osram-osledfundamentalsdrivingledsac-dcpowersupplies06-26-2012-121218095105-phpapp01

LED F d t l
LED
F
un
d
amen
t
a
l
s
Driving LEDs –
AC
-
DC Power
AC
DC
Power
Supplies
06-26-2012

Introduction
Normalized Spectrum Behavior at 24, 35, 50, 70 Degree Celsius
1,00
T
Y
Proper driving of LEDs is required to
address some of the fundamental
variations that all LEDs ma
y
have due to 0,20
0,40
0,60
0,80
INTENSI
T
Spectrum Behavior at 24, 35, 50, 70 Degree Celsius
5,00E-05
6,00E-05
INTENSITY
y
manufacturing tolerances.
There are different methods that are
used to drive LEDs These methods can
0,00580 590 600 610 620 630 640 650 660 670 680
WAVELENGTH [nm]
0
,
00E+00
1,00E-05
2,00E-05
3,00E-05
4,00E-05
WAVELENGTH [nm]
used
to
drive
LEDs
.
These
methods
can
be very simple or complicated depending
on the application.
,
380 430 480 530 580 630 680 730 780
Some of the key parameters needed to
choose proper driving include, expected
Tj (Junction Temperature), expected Vf
mismatch between LEDs, color accuracy
needed at the system level and if
dimming of LEDs is required.
LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 2

Need for Current Regulation in LED Systems
The I-V characteristics of an LED plays a key
role in deciding what type of regulation, current
or volta
g
e is best suited for drivin
g
LEDs.
gg
Due to the fact that there’s a small increase in
voltage once the threshold is reached, will
significantly increase current through an LED
significantly
increase
current
through
an
LED
,
regulating current is more ideal for driving
LEDs.
Also, current regulation is required in LED
system to control and maintain:
»Color shift VS LED current
Flux or light output VS LED current
»
Flux
or
light
output
VS
LED
current
There are three commonly adopted methods of
drivin
g
LEDs
;
resistor based
,
linear re
g
ulators
,
LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 3
g; , g ,
and switching regulators.

Driving Options
LED
LED
s
Electrical characteristics Optical characteristics Thermal characteristics
Driving options
Linear drivers
Switching drivers
Discrete based drive
- Resistor based
- Transistor based
Linear
drivers
- Fixed voltage
- constant current
Switching
drivers
-DC-DC drivers
-AC-DC drivers
LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 4

Driving Options…
Discrete drive
Switching drivers
can be DC-DC or
AC
DC
AC
DC is
AC
-
DC
.
AC
-
DC
is
covered in this
presentation.
LED Fundamentals | Driving LEDs - AC-DC Power Supplies | Page 5