Reference Design
Lighting Power Products
Longmont Design Center
LM3444 MR16 Boost Reference Design for
Non-Dimming & Dimming LED Applications
Feb 13, 2012
Revision 3.0
NATIONAL SEMICONDUCTOR
Page 1 of 20
Table of Contents
MR16 Halogen/SSL Retro-Fit Analysis ...................................................................................................................... 3
Differences between Magnetic and Electronic Transformers .................................................................................................... 3
SSL MR16 lamps compatibility concerns with ELVT and ELV dimmers (true retro-fit) ............................................................... 3
Halogen vs SSL MR16 waveforms ............................................................................................................................................... 4
Halogen MR16 .............................................................................................................................................................. 5
LM3444 MR16 Boost Reference Design .................................................................................................................... 7
Operating Specifications ............................................................................................................................................................. 7
Schematic.................................................................................................................................................................................... 8
PCB Layout .................................................................................................................................................................................. 8
Bill of Materials ........................................................................................................................................................................... 9
Typical Performance ................................................................................................................................................................ 10
Dimming Waveforms ................................................................................................................................................................ 13
Thermal Analysis .......................................................................................................................................................15
Reference Design Transformer Compatibility ........................................................................................................16
Performance with and without Transformer ...........................................................................................................17
Revision History .........................................................................................................................................................20
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 2 of 20
MR16 Halogen/SSL Retro-Fit Analysis
Differences between Magnetic and Electronic Transformers
Magnetic Transformers
Magnetic transformers step down 120VAC line voltage to 12VAC. Magnetic transformers consist only of magnetic
core, and copper wire, no electronics are used to step down the voltage from 120VAC to 12VAC. Due to the fact
that the frequency of operation is 50Hz or 60Hz, the size of the Magnetic transformers is large and heavy. Magnetic
transformers are primarily available in two types of construction; torroidal and laminated EI core.
With existing Halogen MR16 systems that require dimming, Magnetic Low Voltage Dimmers are required to be
used.
Electronic Transformers
Electronic transformers also step down 120VAC line voltage to 12VAC. Electronic transformers are much smaller
and more efficient than magnetic transformers. Electronic transformers are more common than magnetic
transformers in existing Halogen MR16 system. Electronic Low Voltage Transformers (ELVT) consists of a small
self resonant tank power supply. Electronic Low Voltage Dimmers (ELV dimmers) are used with ELVT for dimming
systems.
Although electronic transformers are more complex, with many more components, that their magnetic counterparts,
electronic transformers are far less expensive and smaller. The shear amount of core material and copper within a
magnetic transformer adds cost, and the weight of the product makes it expensive to manufacture, and ship.
SSL MR16 lamps compatibility concerns with ELVT and ELV dimmers (true retro-fit)
Electronic transformers modulate (PWM) the input AC voltage with a frequency of 35 kHz to150 kHz. This
waveform is step-down from 120V or 230V (typical) to 12VAC with a transformer. The higher switching frequency
allows for the smaller magnetic components, and the overall smaller design. As mentioned earlier, the electronic
transformer is a self driven resonant half bridge topology. The self resonance half-bridge topology requires the
converter to have a minimal load at all times to function properly. Common minimum loads for ELV dimmers are
from 6W – 12W depending on manufacture, and maximum power rating of the ELVT. With traditional Halogen
lamps, the minimal load is of no concern, common Halogen MR16 lamps use about 50W of power per lamp. These
lamps are very inefficient, and 10W of Halogen power produces very little light.
With the current efficacy of the LEDs above 100 lumens per watt, 6W of SSL power is equivalent to about 40W to
50W of Halogen power. One can quickly see the compatibility issue of SSL MR16 lamps and the ELVT’s. If the
output power of the ELVT reduces below the minimum requirement, the ELV dimmer will stop operating. The
turning on, and off of the ELVT will cause visible flicker from the SSL MR16 lamp, and could also cause reliability
issues with the lamp or ELVT.
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 3 of 20
Halogen vs SSL MR16 waveforms
Halogen MR16 waveforms
Improper SSL MR16 operating waveform
Channel - 1 (yellow trace) = Input line voltage
Channel - 3 (purple trace) = Input line current
Channel - 4 (green trace) = bulb current
Issue #1 - The two scope captures above illustrate the SSL MR16 technical challenges. Figure one shows typical
Halogen MR16 waveforms, and figure two is common MR16 replacement bulbs waveforms. The SSL replacement
bulb looks capacitive to the ELVT; therefore large current spikes charge the energy storage device within the SSL
MR16 bulb. The switching converter within the bulb then processes the input power from the energy storage
element to the LED load. At this time the minimum load requirement of the ELVT is not satisfied, and the ELVT
turns off. Once the energy is depleted within the MR16 converter, the ELVT will start up, and the process cycles.
The turning off/on of the ELVT will manifest itself as visible flicker.
Issue #2 – The maximum input current to the Halogen bulb is approximately 4.25A. The maximum input current to
the SSL bulb is approximately 12A. The large magnitude spike associated with charging the SSL MR16 input
capacitor can cause premature failures within the SSL bulb, or even the ELVT.
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 4 of 20
Halogen MR16
Summary: No flickering observed. There is a delay (1.12ms, 24° angle) from when the supply voltage starts
ramping up from zero volts to when the electronic transformer starts to operate and the bulb turns on. This delay
shows up on the LED MR16s as well although the magnitude of delay does vary from bulb to bulb. No current
spikes observed out of the transformer.
The bench set-up diagram below was used in the evaluation of the halogen MR16 bulb. The following scope plots
show voltage and current waveforms designated by the labels indicated in the bench set-up diagram. The
electronic transformer used was the Lightech LET-75.
Bench Circuit
IIN
LINE
120VAC
Power
Supply
LINE
VIN
NEUTRAL
+12V
12V, 50W Halogen
MR16 Bulb
IBULB
Transformer
(Electronic)
NEUTRAL
SGND
VBULB
VIN (Yellow), IIN (Magenta), IBULB (Green)
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 5 of 20
VIN (Yellow), IIN (Magenta), IBULB (Green)
VBULB (Blue), IBULB (Green)
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 6 of 20
LM3444 Boost MR16 Reference Design
This reference design was based on the released LM3444 IC from National Semiconductor.
This design was developed to minimize the current spikes coming out of an electronic transformer to less than 5A,
which is a typical transformer rating, when driving an LED MR16 circuit. The off the shelf LED MR16 solutions
exhibit spikes that significantly exceed a transformer’s maximum rated output current which will degrade the
reliability of the transformer and reduce its operating lifetime.
This design generates a continuous LED current when a 220uF 35V electrolytic capacitor is placed across the
output. The circuit operates in a constant output power mode. The output power is fixed at about 6W.
Operating Specifications
NOTE: The following specifications are typical values based on the LED driver being powered directly by a 12VAC
supply (i.e. no electronic or magnetic step-down transformer).
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 23.5V (Single string of 7 LEDs)
Input Current, IIN .................................................................................................................................................. 710mA
LED Output Current, ILED ..................................................................................................................................... 280mA
Input Power, PIN .................................................................................................................................................. ~ 8.0W
Output Power, POUT ............................................................................................................................................. ~ 6.6W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 26.6V (Single string of 8 LEDs)
Input Current, IIN .................................................................................................................................................. 680mA
LED Output Current, ILED ..................................................................................................................................... 240mA
Input Power, PIN .................................................................................................................................................. ~ 7.7W
Output Power, POUT ............................................................................................................................................. ~ 6.4W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 28.2V (Single string of 9 LEDs)
Input Current, IIN .................................................................................................................................................. 670mA
LED Output Current, ILED ..................................................................................................................................... 220mA
Input Power, PIN .................................................................................................................................................. ~ 7.5W
Output Power, POUT ............................................................................................................................................. ~ 6.2W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
SMPS Topology .................................................................................................................................................... Boost
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 7 of 20
PCB Schematic
PCB Layout
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 8 of 20
Bill of Materials
Designator
Description
MFG
Part Number
C1
CAP, CERM, 1.0uF, 25V, +/-10%, X5R, 0805
MuRata
GRM216R61E105KA12D
C2
CAP, ELECT, 220uF, 35V, +/-20%, Radial 8x11.5mm
Panasonic
ECA-1VHG221
C3
CAP, CERM, 22uF, 25V, +/-10%, X5R, 1210
MuRata
GRM32ER61E226KE15L
C4
CAP, CERM, 330pF, 100V, +/-5%, X7R, 0603
AVX
06031C331JAT2A
C5
CAP, CERM, 4.7uF, 50V, +/-10%, X7R, 1210
MuRata
GRM32ER71H475KA882
C6
CAP, CERM, 4.7uF, 25V, +/-10%, X5R, 0805
MuRata
GRM21BR61E475KA12L
D1-D4
Diode, Schottky, 30V, 3A, SMA
Diodes Inc.
B330A-13-F
D5
Diode, Schottky, 60V, 1A, SMA
Diodes Inc.
B160-13-F
D6
TVS BI-DIR 24V 400W SMA (Optional)
Diodes Inc
SMAJ24CA-13-F
D7
Diode, Zener, 11V, 500mW, SOD-123
Central Semiconductor
CMHZ4698
D8
Diode, Zener, 33V, 500mW, SOD-123
Central Semiconductor
CMHZ4714
D9
Diode, Schottky, 75V, 150mA, SOD-323
Fairchild
1N4148WS
L1
Ind, Shielded Drum Core, Ferrite, 33uH, 1.1A, 0.31 ohm, SMD
Coilcraft
MSS6132-333MLB
Q1
Transistor, NPN, 80V, 500mA, SOT-23
Central Semiconductor
CMPTA06
Q2
MOSFET, N-CH, 60V, 1.2A, SOT-23
Diodes Inc.
ZXMN6A07FTA
R1
RES, 0.1 ohm, 5%, 0.125W, 0805
Panasonic
ERJ-6RSJR10V
R2, R4
RES, 1.00k ohm, 1%, 0.1W, 0603
Vishay-Dale
R3
RES, 12.4k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW06031K00FKEA
ERJ-6GEYJ4R7V
CRCW060312k4FKEA
R5
RES, 1.00 ohm, 1%, 0.5W, 1206
Stackpole Electronics Inc
CSR1206FK1R00
R6
RES, 4.7 ohm, 5%, 0.125W, 0805
Yageo
RC0805JR-074R7L
U1
AC-DC Off Line LED Driver
National Semiconductor
LM3444MM
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 9 of 20
Typical Performance (Eight series LEDs)
Bench Circuit
I1
LINE
120VAC
Power
Supply
NEUTRAL
I3
I2
Vp
Vs
Transformer
V1
(Electronic)
Vp
Vs
VIN
V2
LM3444 MR16
LED Driver
VIN
LED
Board
LED+
V3
LED-
The following scope plots show voltage and current waveforms designated by the labels indicated in the following
bench set-up diagram. The electronic transformer used was the Lightech LET-75.
CH2 V1 Voltage, CH4 I3 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 10 of 20
CH2 V1 Voltage, CH4 I2 Current
4.4A peak
CH2 V1 Voltage, CH4 I2 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 11 of 20
CH2 V2 Voltage, CH4 I2 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 12 of 20
LM3444 MR16 Boost evaluation board Dimming Waveforms
Bench Circuit
I1
Vp
LINE
120VAC
Power
Supply
V1
Triac
Dimmer
V2
NEUTRAL
I4
I3
I2
Vs
Transformer
( Electronic )
Vp
Vs
VIN
V3
VIN
LED
Board
LED+
LM3444 MR16
LED Driver
V4
LED-
This LM3444 MR16 Boost evaluation board is designed to operate (flicker-free) with common Electronic Low
Voltage dimmers, and Electronic Transformers.
Dimmer Used – Lutron SELV-300P-GR
Electronic Transformer – Lightech LET75
20:1 dimming ratio
LM3444 MR16 Boost - Eight series connected LEDs at 200mA (90° Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 13 of 20
LM3444 MR16 Boost - Eight series connected LEDs at 100mA (45° Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444 MR16 Boost - Eight series connected LEDs at 10mA (minimum Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 14 of 20
Thermal Analysis
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 15 of 20
Reference Design Transformer Compatibility
The following transformers were tested with the National LED driver designs described in this document. A
compatibility matrix is shown below which describes which driver/transformer combinations are suitable (i.e. no
flicker, stable operation).
Electronic Transformers (120VAC to 12VAC):
Lightech, Model: LET-60, 60W
Lightech, Model: LET-75, 75W
Lightech, Model: LET-60 LW, 60W
Hatch, Model: RS12-80M, 80W
Hatch, Model: RS12-60, 60W
Pony, Model: PET-120-12-60, 60W
Eurofase, Model: 0084 CLASS 2, 60W
Magnetic Transformers (120VAC to 12VAC):
Hatch, Model: LS1275EN, 75VA
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 16 of 20
Performance with 7 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 7 LEDs
11.91
0.708
7.97
23.55
0.281
6.62
83.0%
0.948
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
LM3444 BOOST 7 LEDs
120
0.07
8.18
23.5
0.270
6.23
77.6%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 7 LEDs
2 LEDs
120@ 1A
0.072
8.13
23.5
0.270
6.23
78.0%
0.934
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 17 of 20
Performance with 8 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 8 LEDs
11.91
0.682
7.66
26.64
0.238
6.34
82.8%
0.946
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 8 LEDs
120
0.067
7.86
26.5
0.230
6.10
77.5%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 8 LEDs
2 LEDs
120@ 1A
0.069
7.82
26.5
0.230
6.10
77.9%
0.930
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 18 of 20
Performance with 9 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 9 LEDs
11.92
0.668
7.51
28.25
0.220
6.22
82.8%
0.946
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 9 LEDs
120
0.066
7.74
28.0
0.215
6.02
77.8%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 9 LEDs
2 LEDs
120@ 1A
0.068
7.64
28.0
0.212
5.94
77.7%
0.930
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 19 of 20
Revision History
Date
10/14/2011
02/13/2012
Author
David Zhang
David Zhang
Revision
2
3
LM3444-MR16-Boost Reference Design
Description
Added D9
Change D9 P/N
NATIONAL SEMICONDUCTOR
Page 20 of 20
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,
and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should
obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are
sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard
warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where
mandated by government requirements, testing of all parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,
or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a
warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual
property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied
by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive
business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional
restrictions.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all
express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not
responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably
be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing
such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be
provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in
such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at
the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are
designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated
products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Mobile Processors
www.ti.com/omap
Wireless Connectivity
www.ti.com/wirelessconnectivity
TI E2E Community Home Page
e2e.ti.com
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2012, Texas Instruments Incorporated