LED Lighting Solutions
Summer 2010
Adding Intelligence to Lighting Applications
LED Lighting Design Guide
www.microchip.com/lighting
LED Lighting Solutions
Table of Contents
LED Lighting ................................................................ 3
LED Applications ......................................................... 3
Efficient LED Control .................................................... 3
Driving LEDs with a Charge Pump ................................. 4
MCP1252 Charge Pump Backlight
Demonstration Board (MCP1252DM-BKLT) ................. 4
Driving LEDs with a Boost Regulator ............................. 4
MCP1650 Multiple White LED
Demonstration Board (MCP1650DM-LED2) ................. 5
Driving LEDs with a SEPIC Regulator .............................. 5
MCP1650 3W White LED Demonstration Board
(MCP1650DM-LED1) ................................................. 5
High Efficiency LED Smart Driver.................................... 6
Adding Intelligence – PIC10F Solutions .......................... 7
Provide Simple Dimming Control .................................... 8
Integrate Multiple Tasks –
PIC12 and PIC16 Mixed Signal Solutions ....................... 8
Internal 5V Regulator .................................................... 8
Generating PWM Control Signals ................................... 9
Mixed-Signal LED Drivers .............................................. 10
MCP1630 and MCP1631 High-Speed
PWM Controllers .......................................................... 11
MCP1630 Boost Mode LED Driver
Demonstration Board (MCP1630DM-LED2) ................. 11
MCP1631HV Digitally Controlled Programmable
Current Source Reference Design
(MCP631RD-DCPC1) ................................................. 11
Digital Control vs. Analog Control ................................... 12
Low Cost Digital Control ................................................ 12
High Performance Digital Control ................................... 13
Wired Communication Solutions for Lighting
0-10V Interface ......................................................... 14
Digitally Addressable Lighting Interface (DALI) ............. 14
DALI Ballast Software Library ..................................... 14
DMX512 .................................................................. 14
Advanced Communication Solutions for Lighting
ZigBee® Protocol....................................................... 15
MiWi™ Protocol ........................................................ 15
MiWi™ P2P Protocol ................................................. 15
Wi-Fi Interface .......................................................... 15
USB Interface ........................................................... 16
Ethernet Interface ..................................................... 16
CAN and LIN Protocols .............................................. 16
Automotive Ambient Lighting Module
Reference Design (APGRD004)
.................................. 16
Temperature Sensing Solutions for
Power LED Applications ................................................ 17
Logic Output Temperature Sensors ................................ 17
Resistor-Programmable Temperature Switches ............... 17
Using TC6501 Open Drain Output for
Current Set-Point Control .............................................. 18
Using the TC6501 to Provide MCU Interrupt ................... 18
Fan Controller Application Using TC6502 ....................... 18
Voltage Output Temperature Sensors ............................. 19
Power LED Thermal Control Circuit Using
MCP9700 and MCP1650 ............................................. 19
2
LED Lighting Solutions Design Guide
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LED Lighting Solutions
LED Lighting
LEDs are no longer used just for providing the pretty red and
green indicator lights on electronic equipment. Advances
in technology have allowed LEDs to be used as practical
sources of illumination. The primary benefits of LEDs are
long life, durability and efficiency. When driven properly, a
power LED can last tens of thousands of hours without a
degradation of light output. The typical efficacy of a power
LED, measured in lumens per watt, is 40-80. This is several
times greater than incandescent light sources and is only
exceeded by fluorescent light sources. Since the LED is a
solid-state device, it can withstand shock and vibration that
would damage a filament bulb.
Efficient LED Control
LEDs must be driven with a source of constant current. Most
LEDs have a specified current level that will achieve the
maximum brightness for that LED without premature failures.
An LED could be driven with a linear voltage regulator
configured as a constant current source. However, this
approach is not practical for higher power LEDs due to power
dissipation in the regulator circuit. A switch-mode power
supply (SMPS) provides a much more efficient solution to
drive the LED.
An LED will have a forward voltage drop across its terminals
for a given current drive level. The power supply voltage and
the LED forward voltage characteristics determine the SMPS
topology that is required. Multiple LEDs can be connected
in series to increase the forward voltage drop at the chosen
drive current level.
The SMPS circuit topologies adopted to regulate current
in LED lighting applications are the same used to control
voltage in a power supply application. Each type of SMPS
topology has its advantages and disadvantages as presented
in the table below.
This design guide presents two types of LED driver solutions.
First, an analog driver IC can be used independently or
together with a MCU for added intelligence. Second, the LED
drive function can be integrated into the MCU application.
LED Applications
The benefits of LED lighting are helpful in many types of
lighting applications:
■
Automotive and aircraft cabin lighting
■
Automotive and aircraft instrument panel lighting
■
Architectural emergency exit lighting
■
Architectural color effect lighting
■
Industrial and outdoor lighting
■
Traffic and railway signals
■
Automotive brake lights
■
Dot matrix signs and video displays
■
LCD display backlighting
■
Personal flashlights
■
Medical instrument and tool lighting
■
Digital camera flash and video light
Literature on the Web
■
AN1114 – Switch Mode Power Supply (SMPS)
Topologies (Part I), DS01114
■
AN1207 – Switch Mode Power Supply (SMPS)
Topologies (Part II), DS01207
Common SMPS Topologies Useful for LED Lighting
Regulator
Topology
Charge Pump
Buck
Boost
SEPIC
Buck-Boost
V
IN
to V
OUT
Relationship
-V
OUT
< V
IN
< V
OUT
V
IN
> V
OUT
V
IN
< V
OUT
V
OUT
< V
IN
< V
OUT
V
OUT
< V
IN
< V
OUT
Depends on
transformer
Complexity
Low
Medium
Medium
Medium
Medium
Medium
Component
Count
Medium
Medium
Medium
High
Medium
Medium
Comments
– Limited I
OUT
range
– No inductors
– Chopped I
IN
– High side drive
– Extra parts needed to isolate
output from input
– Smooth I
IN
– Multiple outputs
– Two inductors
– Single inductor
– Up to four switches
– Transformer can provide electrical
isolation
– Multiple outputs possible
Flyback
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LED Lighting Solutions Design Guide
3
LED Lighting Solutions
Driving LEDs with a Charge Pump
A charge pump power supply does not have inductors that
are required in other SMPS topologies. This provides a
more compact and less expensive circuit. The downside is
that charge pumps cannot supply large amounts of current
compared to the other topologies. Charge pump circuits
are most useful for backlighting applications. Common
applications include PCs, LCD displays and automotive
instrumentation.
Driving LEDs with a Boost Regulator
A boost regulator topology is used when the output voltage
of the converter must be equal to or greater than the input
voltage. A boost regulator is useful for driving a chain of
LEDs connected in series. It is beneficial to drive multiple
LEDs in series. This ensures that all LEDs receive the same
amount of current and will have the same brightness level.
Using a coupled inductor in the boost circuit reducing the
switching voltage requirements of the MOSFET switch.
The MCP1640 synchronous boost regulator can provide
a stable operating voltage for an LED from a single cell
alkaline battery.
The MCP1650 Boost Regulator uses an external switch
so that it can be used for any type of load. An additional
advantage of the MCP1650 in battery applications is the
Gated Oscillator Architecture which provides 2 duty cycles
reducing high-peak inductor current and output ripple
voltages. Input voltages above 3.8V engage a 56% duty
cycle and an 80% duty cycle when the input voltage drops
below 3.8V, extending battery life in these applications.
MCP1640 Single Cell Synchronous Boost Regulator
L
1
4.7 μH
MCP1252 Charge Pump Backlight
Demonstration Board
(MCP1252DM-BKLT)
Demonstrates the use of a charge
pump device in an LED application
and acts as a platform to evaluate
the MCP1252 device in general.
Light intensity is controlled
uniformly through the use of ballast
resistors. A PIC10F206 MCU
provides an enable signal to the MCP1252 and accepts a
push-button input that allows the white LEDs to be adjusted
to five different light intensities.
Literature on the Web
■
MCP1252/3 Data Sheet, DS21572
■
MCP1252 Charge Pump Backlight Demo Board
User’s Guide, DS51551
■
MCP1252/3 Evaluation Kit User’s Guide, DS51313
■
DG10 – Power Solutions Design Guide, DS21913
SW
V
IN
0.9V to 1.7V
C
IN
4.7 μF
Alkaline
V
OUT
V
IN
V
OUT
3.3V @ 100 mA
MCP1640
EN
V
FB
976 KΩ
C
OUT
10 μF
562 KΩ
GND
Charge Pump LED Driver Using the MCP1252
5
C-
6
C+
V
OUT
3
V
IN
2
8
Single
Li-Ion
Cen
MCP1252-ADJ
7
1
SHDN
FB
PG
GND
4
PWM Brightness
Control
4
LED Lighting Solutions Design Guide
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LED Lighting Solutions
MCP1650 Multiple White LED Demonstration Board
(MCP1650DM-LED2)
The MCP1650 Multiple White LED Demo
Board uses the MCP1650 IC to power the
nine white LEDs which are connected in
series. A PIC10F202 microcontroller in a
SOT-23 6-pin package is used to provide the
PWM signal to the MCP1650. It also accepts
a push button input that allows the user
to adjust the white LEDs to three different
intensities of 100%, 50% and 25%.
Driving LEDs with a SEPIC Regulator
The Single-Ended Primary Inductance Converter (SEPIC)
regulator topology uses an additional inductor, but provides
the following advantages for battery powered applications:
■
The converter can buck or boost as the input voltage
changes.
■
The circuit topology provides inherent short-circuit
protection due to the use of a coupling capacitor.
MCP1650 3W White LED Demonstration Board
(MCP1650DM-LED1)
Demonstrates the MCP165X Boost Controller
product family in a battery-powered white LED
application with an input voltage range of 2.0V
to 4.5V.
Literature on the Web
■
MCP1640/B/C/D Data Sheet, DS22234
■
MCP1650/51/52/53 Data Sheet, DS21876
■
MCP1650 Multiple White LED Demo Board
User’s Guide, DS51586
■
AN948 – Efficiently Powering Nine White LEDs
Using the MCP1650, DS00948
■
AN980 – Designing a Boost-Switching Regulator with
the MCP1650, DS00980
■
DG10 – Power Solutions Design Guide, DS21913
Literature on the Web
■
MCP1650 3W White LED Demo Board User’s Guide,
DS51513
Battery Operated Boost LED Driver Example Using the MCP1650
V
IN
V
BAT
EXT
MCP1650
CS
NC
+
-
9 LEDs
33V/15 mA
NC
ON
OFF
FB
SHDN
GND
Battery Input to 3.6V 3W LED Driver (SEPIC Converter)
V
BAT
V
BAT
3W
LED
V
IN
V
BAT
+
-
4.5-2.0V
EXT
MCP1651
CS
FB
LBI
LBO
Low Battery
Warning
ON
OFF
SHDN
GND
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LED Lighting Solutions Design Guide
5
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