This demonstration board highlights the performance of a LM3444 based Flyback LED driver solution that
can be used to power a single LED string consisting of 4 to 8 series connected LEDs from an 90 V
135 V
conditions are summarized in this application note.
This is a two-layer board using the bottom and top layer for component placement. The demonstration
board can be modified to adjust the LED forward current, the number of series connected LEDs that are
driven and the switching frequency. Refer to the LM3444 AC-DC Offline LED Driver (SNVS682) data
sheet for detailed instructions.
A bill of materials is included that describes the parts used on this demonstration board. A schematic and
layout have also been included along with measured performance characteristics.
, 60 Hz input power supply. The key performance characteristics under typical operating
RMS
User's Guide
SNVA454E–September 2010–Revised May 2013
Driver
to
RMS
2Key Features
•Line injection circuitry enables PFC values greater than 0.99
•Adjustable LED current and switching frequency
•Flicker free operation
3Applications
•Solid State Lighting
•Industrial and Commercial Lighting
•Residential Lighting
4Performance Specifications
Based on an LED Vf= 3.57V
SymbolParameterMinTypMax
V
IN
V
OUT
I
LED
P
OUT
f
sw
Input voltage90 V
LED string voltage12 V21.4 V30 V
LED string average current-350 mA-
Output power-7.6 W-
Switching frequency-79 kHz-
RMS
120 V
RMS
135 V
RMS
PowerWise is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
SNVA454E–September 2010–Revised May 2013AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver
LM3444 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
5LM3444 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
WARNING
TheLM3444evaluationboardhasexposedhighvoltage
SNVA454E–September 2010–Revised May 2013AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver
Submit Documentation Feedback
components that present a shock hazard. Caution must be taken
when handling the evaluation board. Avoid touching the evaluation
board and removing any cables while the evaluation board is
operating.Isolatingtheevaluationboardratherthanthe
oscilloscope is highly recommended.
The ground connection on the evaluation board is NOT referenced
to earth ground. If an oscilloscope ground lead is connected to the
evaluation board ground test point for analysis and AC power is
applied, the fuse (F1) will fail open. The oscilloscope should be
powered via an isolation transformer before an oscilloscope
ground lead is connected to the evaluation board.
The LM3444 evaluation board should not be powered with an open
load. For proper operation, ensure that the desired number of LEDs
are connectedat theoutput beforeapplying powerto the
evaluation board.
6LM3444 Device Pin-Out
www.ti.com
WARNING
WARNING
Pin #NameDescription
10NCNo internal connection.
4
AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED DriverSNVA454E–September 2010–Revised May 2013
Table 1. Pin Description 10-Pin VSSOP
1NCNo internal connection.
2NCNo internal connection.
3NCNo internal connection.
4COFFOFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant
5FILTERFilter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming
6GNDCircuit ground connection.
7ISNSLED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the
8GATEPower MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
9V
OFF time of the switching controller.
input.
maximum LED current.
controller.
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
The LED driver is designed to accurately emulate an incandescent light bulb and therefore behave as an
emulated resistor. The resistor value is determined based on the LED string configuration and the desired
output power. The circuit then operates in open-loop, with a fixed duty cycle based on a constant on-time
and constant off-time that is set by selecting appropriate circuit components.
13.1Performance
In steady state, the LED string voltage is measured to be 21.38 V and the average LED current is
measured as 357 mA. The 120 Hz current ripple flowing through the LED string was measured to be 170
mA
connected across the output port. The ripple current can be reduced by increasing the value of energy
storage capacitor or by increasing the LED string voltage.
The LED driver switching frequency is measured to be close to the specified 79 kHz. The circuit operates
with a constant duty cycle of 0.28 and consumes 9.25 W of input power. The driver steady state
performance for an LED string consisting of 6 series LEDs is summarized in the following table.
at full load. The magnitude of the ripple is a function of the value of energy storage capacitors
pk-pk
Table 2. Measured Efficiency and Line Regulation (6 LEDs)
The LED driver is able to achieve close to unity power factor (P.F. ~ 0.99) which meets Energy Star
requirements. This design also exhibits low current harmonics as a percentage of the fundamental current
(as shown in Figure 17) and therefore meets the requirements of the IEC 61000-3-2 Class-3 standard.
Electromagnetic Interference (EMI)
Figure 17. Current Harmonic Performance vs. EN/IEC61000-3-2 Class C Limits
14Electromagnetic Interference (EMI)
The EMI input filter of this evaluation board is configured as shown in the following circuit diagram.
Figure 18. Input EMI Filter and Rectifier Circuit
SNVA454E–September 2010–Revised May 2013AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver
In order to get a quick estimate of the EMI filter performance, only the PEAK conductive EMI scan was
measured and the data was compared to the Class B conducted EMI limits published in FCC – 47, section
15.
Figure 19. Peak Conductive EMI Scan per CISPR-22, Class B Limits
If an additional 33nF of input capacitance (C6) is utilized in the input filter, the EMI conductive
performance is further improved as shown in Figure 20.
www.ti.com
14
Figure 20. Peak Conductive EMI Scan With Additional 33nF of Input Capacitance
AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED DriverSNVA454E–September 2010–Revised May 2013
16.1Injecting Line Voltage Into FILTER (Achieving PFC > 0.99)
If a small portion (750mV to 1.00V) of line voltage is injected at FILTER of the LM3444, the circuit is
essentially turned into a constant power flyback, as shown in Figure 23.
Circuit Analysis and Explanations
Figure 23. Line Voltage Injection Circuit
The LM3444 works as a constant off-time controller normally, but by injecting the 1.0V rectified AC voltage
into the FILTER pin, the on-time can be made to be constant. With a DCM Flyback, Δi needs to increase
as the input voltage line increases. Therefore a constant on-time (since inductor L is constant) can be
obtained.
By using the line voltage injection technique, the FILTER pin has the voltage wave shape shown in
Figure 24 on it. Voltage at V
peak should be kept below 1.25V. At 1.25V current limit is tripped. C11
FILTER
is small enough not to distort the AC signal but adds a little filtering.
Although the on-time is probably never truly constant, it can be observed in Figure 25 how (by adding the
rectified voltage) the on-time is adjusted.
Figure 24. FILTER Waveform
SNVA454E–September 2010–Revised May 2013AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver
inductor increases, and the peak current increases.
1V
D x LED Current
Circuit Analysis and Explanations
For this evaluation board, the following resistor values are used:
R2 = R7 = 309kΩ
R15 = 3.48kΩ
Therefore the voltages observed on the FILTER pin will be as follows for listed input voltages:
For VIN = 90V
For VIN = 120V
For VIN = 135V
RMS
RMS
RMS
, V
FILTER
, V
, V
Using this technique, a power factor greater than 0.99 can be achieved without additional passive active
power factor control (PFC) circuitry.
FILTER
FILTER
www.ti.com
= 0.71V
= 0.95V
= 1.07V
18
Figure 25. Typical Operation of FILTER Pin
AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED DriverSNVA454E–September 2010–Revised May 2013
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license 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 significant portions 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. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
ProductsApplications
Audiowww.ti.com/audioAutomotive and Transportationwww.ti.com/automotive
Amplifiersamplifier.ti.comCommunications and Telecomwww.ti.com/communications
Data Convertersdataconverter.ti.comComputers and Peripheralswww.ti.com/computers
DLP® Productswww.dlp.comConsumer Electronicswww.ti.com/consumer-apps
DSPdsp.ti.comEnergy and Lightingwww.ti.com/energy
Clocks and Timerswww.ti.com/clocksIndustrialwww.ti.com/industrial
Interfaceinterface.ti.comMedicalwww.ti.com/medical
Logiclogic.ti.comSecuritywww.ti.com/security
Power Mgmtpower.ti.comSpace, Avionics and Defensewww.ti.com/space-avionics-defense
Microcontrollersmicrocontroller.ti.comVideo and Imagingwww.ti.com/video
RFIDwww.ti-rfid.com
OMAP Applications Processorswww.ti.com/omapTI E2E Communitye2e.ti.com
Wireless Connectivitywww.ti.com/wirelessconnectivity