Texas Instruments Incorporated AN-2127 User's Guide

AN-2127 LM3448 A19 Edison Retrofit Evaluation Board

1 Introduction

This demonstration board highlights the performance of a LM3448 non-isolated LED driver solution that can be used to power a single LED string consisting of eight to twelve series connected LEDs from a 85 V

to 135 V

RMS

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. The topology used for this evaluation board eliminates the need for passive power factor correction and results in high power factor with minimal component count which results in a size that can fit in a standard A19 Edison socket. This board will also operate correctly and dim smoothly using most standard TRIAC dimmers.

Refer to the LM3448 Phase Dimmable Offline LED Driver with Integrated FET (SNOSB51) data sheet for detailed information regarding the LM3448 device. A schematic and layout have also been included along with measured performance characteristics. A bill of materials is also included that describes the parts used on this demonstration board.

, 60 Hz input power supply.

RMS

User's Guide

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2 Key Features

• Drop-in compatibility with TRIAC dimmers

• Line injection circuitry enables PFC values greater than 0.85

• Adjustable LED current and switching frequency

• Flicker free operation

3 Applications

• Retrofit TRIAC Dimming

• Solid State Lighting

• Industrial and Commercial Lighting

• Residential Lighting

4 Performance Specifications

Based on an LED Vf= 3V

Symbol Parameter Min Typ Max

OUT

LED

OUT

Input voltage 85V

LED string voltage - 36V -

LED string average current - 181mA -

Output power - 6.5W -

RMS

120V

RMS

135V

RMS

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20 40 60 80 100 120

100

150

200

LED CURRENT (mA)

INPUT VOLTAGE (V

RMS

)

Performance Specifications

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Figure 1. Demo Board

Figure 2. LED Current vs. Line Voltage (using TRIAC Dimmer)

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80 90 100 110 120 130 140

100

150

200

250

300

350

LED CURRENT (mA)

INPUT VOLTAGE (V

RMS

)

12 LEDs 10 LEDs 8 LEDs

80 90 100 110 120 130 140

OUT

(W)

INPUT VOLTAGE V

RMS

12 LEDs 10 LEDs 8 LEDs

80 90 100 110 120 130 140

EFFICIENCY (%)

INPUT VOLTAGE (V

RMS

)

12 LEDs 10 LEDs 8 LEDs

80 90 100 110 120 130 140

0.78

0.80

0.82

0.84

0.86

0.88

0.90

POWER FACTOR

INPUT VOLTAGE V

RMS

12 LEDs 10 LEDs 8 LEDs

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5 Typical Performance Characteristics

TJ=25°C and VCC=12V, unless otherwise specified.

Figure 3. Efficiency vs. Line Voltage Figure 4. Power Factor vs. Line Voltage

Typical Performance Characteristics

Figure 5. LED Current vs. Line Voltage Figure 6. Output Power vs. Line Voltage

Figure 7. SW FET Drain Voltage Waveform Figure 8. COFF Voltage (CH1), Inductor Current (CH4)

(VIN=120V

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RMS

, 12 LEDs, I

=181mA) (VIN=120V

LED

, 12 LEDs, I

RMS

LED

=181mA)

EMI Performance

6 EMI Performance

120V, 6.5W Conducted EMI Scans

Figure 9. LINE – CISPR/FCC Class B Peak Scan Figure 10. NEUTRAL – CISPR/FCC Class B Peak Scan

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Figure 11. LINE – CISPR/FCC Class B Average Scan Figure 12. NEUTRAL – CISPR/FCC Class B Average

Scan

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Circuit Operation With Forward Phase TRIAC Dimmer

7 Circuit Operation With Forward Phase TRIAC Dimmer

The dimming operation of the circuit was verified using a forward phase TRIAC dimmer. Waveforms captured at different dimmer settings are shown below:

Figure 13. Forward phase circuit at full brightness Figure 14. Forward phase circuit at 90° firing angle

Figure 15. Forward phase circuit at 135° firing angle

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Circuit Operation With Reverse Phase Dimmer

8 Circuit Operation With Reverse Phase Dimmer

The circuit operation was also verified using a reverse phase dimmer and waveforms captured at different dimmer settings are shown below:

Figure 16. Reverse phase circuit at full brightness Figure 17. Reverse phase circuit at 90° firing angle

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Figure 18. Reverse phase circuit at 135° firing angle

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9 Thermal Performance

The board temperature was measured using an IR camera (HIS-3000, Wahl) while running under the following conditions: VIN= 120V

NOTE: Thermal performance is highly dependent on the user's final end-application enclosure, heatsinking methods, ambient operating temperature, and PCB board layout in addition to the electrical operating conditions. This LM3448 evaluation board is optimized to supply 6.5W of output power at room temperature without exceeding the thermal limitations of the LM3448. However higher output power levels can be achieved if precautions are taken not to exceed the power dissipation limits of the LM3448 package or die junction temperature. Please see the LM3448 datasheet for additional details regarding its thermal specifications.

RMS

, I

= 181mA, # of LEDs = 12, P

LED

OUT

Thermal Performance

= 6.5W.

• Cursor 1: 65.3°C

• Cursor 2: 60.1°C

• Cursor 3: 67.6°C

• Cursor 4: 64.9°C

• Cursor 5: 65.6°C

Figure 19. Top Side - Thermal Scan

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Thermal Performance

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• Cursor 1: 68.1°C

• Cursor 2: 64.7°C

• Cursor 3: 62.6°C

• Cursor 4: 61.7°C

Figure 20. Bottom Side - Thermal Scan

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ASNS

DIM

GND

FLTR1

COFF

FLTR2

5 12

BLDR

ISNS

VCC

GND

8 9

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10 LM3448 Device Pin-Out

Pin # Name Description

1, 2, 15, SW Drain connection of internal 600V MOSFET.

3, 14 NC No connect. Provides clearance between high voltage and low voltage pins. Do not tie to GND.

4 BLDR Bleeder pin. Provides the input signal to the angle detect circuitry. A 230Ω internal resistor ensures BLDR is

5, 12 GND Circuit ground connection.

6 V

7 ASNS PWM output of the TRIAC dim decoder circuit. Outputs a 0 to 4V PWM signal with a duty cycle proportional

8 FLTR1 First filter input. The 120Hz PWM signal from ASNS is filtered to a DC signal and compared to a 1 to 3V,

9 DIM Input/output dual function dim pin. This pin can be driven with an external PWM signal to dim the LEDs. It

10 COFF OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the

11 FLTR2 Second filter input. A capacitor tied to this pin filters the PWM dimming signal to supply a DC voltage to

13 ISNS LED current sense pin (internally connected to MOSFET source). Connect a resistor from ISNS to GND to

pulled down for proper angle sense detection.

Input voltage pin. This pin provides the power for the internal control circuitry and gate driver. Connect a

22µF (minimum) bypass capacitor to ground.

to the TRIAC dimmer on-time.

5.85 kHz ramp to generate a higher frequency PWM signal with a duty cycle proportional to the TRIAC dimmer firing angle. Pull above 4.9V (typical) to TRI-STATE® DIM.

may also be used as an output signal and connected to the DIM pin of other LM3448/LM3445 devices or LED drivers to dim multiple LED circuits simultaneously.

constant OFF time of the switching controller.

control the LED current. Could also be used as an analog dimming input.

set the maximum LED current.

LM3448 Device Pin-Out

Figure 21. Device Pin-Out

Table 1. Pin Description 16 Pin Narrow SOIC

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LED +

LED - LINE

NEUTRAL

J10

TP4

TP3

TP1

TP2

Demo Board Wiring Overview

11 Demo Board Wiring Overview

Figure 22. Wiring Connection Diagram

Test Name I/O Description

Point

TP3 LED + Output LED Constant Current Supply

TP4 LED - Output LED Return Connection (not GND)

TP1 LINE Input AC Line Voltage

TP2 NEUTRAL Input AC Neutral

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Table 2. Test Points

Supplies voltage and constant-current to anode of LED string.

Connects to cathode of LED string. Do NOT connect to GND.

Connects directly to AC line or output of TRIAC dimmer of a 120VAC system.

Connects directly to AC neutral of a 120VAC system.

12 Demo Board Assembly

Figure 23. Top View

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R15 C15

DIM

COFF

FLTR2

GND

ISNS

FLTR1

ASNS

BLDR

VCC

GND

LM3448

V+

R22 D8

R14

LED+

LED±

V+

LINE

NEUTRAL

LINE EMI FILTER

COFF

R16

C12

OFF

Current Source

C16

C10

C14

COFF

C13

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13 Design Guide

Design Guide

Figure 24. Bottom View

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Figure 25. Evaluation Board Schematic

R15

C15

V+

LM3448

11 FLTR2

C14

INJECT

Design Guide

13.1 Buck Converter

The following section explains how to design a non-isolated buck converter using the LM3448. Refer to the LM3448 datasheet for specific details regarding the function of the LM3448 device. All reference designators refer to the Evaluation Board Schematic in Figure 25 unless otherwise noted. The circuit operates in open-loop based on a constant off-time that is set by selecting appropriate circuit components. Like an incandescent lamp, the driver is compatible with both forward and reverse phase dimmers.

AC-Coupled Line Injection

By injecting a voltage V input current shaping is obtained which improves power factor performance. By AC-coupling the V signal through capacitor C14, improved line-regulation of the LED current is also achieved (see

Figure 27).

which is proportional to the line voltage into the FLTR2 pin (see Figure 26),

INJECT

Figure 26. FLTR2 Waveform with No Dimmer

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INJECT

Figure 27. AC-Coupled Line-Injection Circuit

Figure 28 shows how line shaping of the input current is implemented. Peak voltage at the FLTR2 pin

should be kept below 1.25V otherwise current limit will be tripped. A good starting point is to set up the resistor divider consisting of resistors R2, R7 and R15 to provide a V

peak input voltage of 1.0V at

INJECT

the input of capacitor C14 at the nominal input voltage. Recommended values for the AC-coupling capacitor C14 is 0.47µF and for the FLTR2 capacitor C15 is 0.1µF.

With a 1.0V V

voltage, the voltage at the FLTR2 pin at the maximum and minimum input voltages can

INJECT

be calculated using the following equations,

(1)

These V

voltages will be used later to determine ripple and peak inductor currents.

FLTR2

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FLTR1

SNS

PWM

I-LIM

1.27V

ISNS

ASNS

GND

FLTR1

FLTR2

DIM

DIM DECODER

4.9V

Tri-State

50k

370k

FLTR2

FLTR1

RAMP GEN.

5.9 kHz

3V 1V

750 mV

125 ns

LEADING EDGE BLANKING

The PWM reference increases

as the line voltage increases.

As line voltage increases, the voltage across the

inductor increases, and the peak current increases.

LED Current

RAMP

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Off-time, On-time and Switching Frequency

The AC mains voltage at the line frequency fLis assumed to be perfectly sinusoidal and the diode bridge ideal. This yields a perfect rectified sinusoid at the input to the buck converter. The maximum, nominal and minimum peak input voltages are defined as follows,

Design Guide

Figure 28. Typical Operation of FLTR2 Pin

The LM3448 will operate as a constant off-time regulator, and so t

will be constant throughout all

OFF

operating points. The on-time tON(and subsequently the switching frequency fSW) will vary depending on input voltage and LED stack voltage values. For this buck converter operating in continuous conduction mode (CCM), the minimum on-time t f

at the maximum peak input voltage,

SW(MAX)

The off-time t

It is important to note that there is a minimum on-time of 200ns that needs to be met in order for proper

is now calculated where T

OFF

LED driver operation.

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can be determined for a maximum desired switching frequency

ON(MIN)

is the minimum switching period,

S(MIN)

(2)

(3)

(4)

SNS

(W)

LED

(mA)

400 370 340 310 280 250 220 190 160

OUT

(W)

9.8

9.1

8.3

7.6

6.8

6.1

5.3

4.6

2.62.52.42.32.22.12.01.91.81.71.61.51.41.3

3.8

SNS

(W)

LED

(mA)

270 250 230 210 190 170 150 130 110

OUT

(W)

9.8

9.1

8.3

7.6

6.8

6.1

5.3

4.6

2.62.52.42.32.22.12.01.91.81.71.61.51.41.3

3.8

SNS

(W)

LED

(mA)

322 298 274 250 226 202 178 154 130

OUT

(W)

9.8

9.1

8.3

7.6

6.8

6.1

5.3

4.6

2.62.52.42.32.22.12.01.91.81.71.61.51.41.3

3.8

Design Guide

Output Power and Current Sense Resistor

Due to the interaction of the AC-coupled line-injection voltage with the FLTR2 signal, the equations for determining the correct sense resistor R desired output power P graphs showing the relationship between LED current, P and Figure 31 for common stack voltages of 8, 10 and 12 LEDs. By referring to these graphs, users can choose R14 values that will meet their LED current and output power requirements.

(shown as R14 in the evaluation board schematic) for a

are complex and beyond the scope of this document. Instead, performance

OUT

SNS

OUT

and R

are shown in Figure 29, Figure 30

SNS

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Figure 29. I

LED

vs. P

OUT

vs. R

SNS

Figure 30. I

LED

for 12 LEDs (Vf=3.0V) for 10 LEDs (Vf=3.0V)

Figure 31. I

LED

vs. P

OUT

vs. R

SNS

for 8 LEDs (Vf=3.0V)

Inductor

Peak inductor currents will need to be calculated as shown below based on the V sense resistor R14 at the maximum and minimum peak input voltages,

vs. P

vs. R

OUT

FLTR2

SNS

voltages and chosen

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(5)

COFF

R16

C12

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Inductor ripple current will need to be specified by the user based on desired EMI performance, inductor size and other operating conditions. The following equations show how to calculate for maximum and minimum inductor ripple currents respectively by basing the ripple (i.e.Δi peak inductor currents,

It is recommended that this buck converter design operate in CCM over the full range of operating peak input voltages, and so the minimum inductor peak current at V

The inductor value can be calculated based on the minimum on-time, LED output voltage and the specified inductor ripple current Δi

COFF Current Source

The current source used to establish the constant off-time is shown in Figure 32.

L-PK(VIN-PK-MAX)

Design Guide

as a percentage of maximum

L(%)

IN-PK(MIN)

should not go below zero,

at the maximum peak input voltage as described below,

(6)

(7)

(8)

Figure 32. COFF Current Source Circuit

Capacitor C12 will be charged with current from the VCCsupply through resistor R16. The COFF pin threshold will therefore be tripped based on the following capacitor equation,

(9)

where,

(10)

Solving for off-time t

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results in,

OFF

(11)

Design Guide

Re-arranging the above equation results in R16 being calculated where C12 is typically chosen as value around 470pF,

Additionally, the maximum on-time t maximum switching period T calculated inductor value, these values can now be calculated as,

Maximum and minimum duty cycles, D voltages respectively,

and corresponding minimum switching frequency f

ON(MAX)

occur at the minimum peak input voltage. Using the previously

S(MAX)

MAX

and D

, will occur at the minimum and maximum peak input

MIN

SW(MIN)

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(12)

and

(13)

(14)

Switching MOSFET (SW FET)

Peak and RMS SW FET currents are calculated along with maximum SW FET power dissipation based on the SW FET R

value using the following equations,

DS-ON

(15)

(16)

and,

(17)

Current Limit

The peak inductor current limit I

should be approximately 25% higher than the maximum operating peak

LIM

inductor current,

(18)

The sense resistor will need to be able to dissipate the maximum power,

(19)

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Re-circulating Diode

The main re-circulating diode (D4) should be sized to block the maximum reverse voltage V operate at the maximum peak I P

as determined by the following equations,

D4(MAX)

DR-PK(MAX)

NOTE: For proper converter operation, the chosen diode should have a reverse recovery time that is less than the LM3448's leading edge blanking time of 125ns.

13.2 Bias Supplies and Capacitances

The VCC bias supply circuit is shown in Figure 33. The passFET (Q1) is used in its linear region to standoff the line voltage from the LM3448 regulator. Both the VCC startup current and discharging of the EMI filter capacitance for proper phase angle detection are handled by Q1. Therefore Q1 has to block the maximum peak input voltage and have both sufficient surge and power handling capability with regards to its safe operating area (SOA). The design equations are,

and RMS currents I

D4-RMS(MAX)

Design Guide

RD4(MAX)

, and dissipate the maximum power

(20)

(21)

(22)

(23)

Note that if additional TRIAC holding current is to be sourced through Q1, then the transistor will need to be sized appropriately to handle the additional current and power dissipation requirements.

(24)

(25)

(26)

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V+

R22

LM3448

6VCC

Design Guide

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Figure 33. Bias Supply Circuit

Input Capacitance

The input capacitors C1 and C10 have to be able to provide energy during the worst-case switching period at the peak of the AC voltage input. They should be high frequency, high stability capacitors (usually metallized film capacitors, either polypropylene or polyester) with an AC voltage rating equal to the maximum input voltage. They should also have a DC voltage rating exceeding the maximum peak input voltage plus half of the peak to peak input voltage ripple specification. The minimum required input capacitance is calculated given the same ripple specification,

(27)

Output Capacitance

C3 should be a high quality electrolytic capacitor with a voltage rating greater than the specified LED stack voltage. Given the desired voltage ripple, the minimum output capacitance is calculated,

(28)

13.3 Input Filter

Background

Since the LM3448 is used for AC to DC systems, electromagnetic interference (EMI) filtering is critical to pass the necessary standards for both conducted and radiated EMI. This filter will vary depending on the output power, the switching frequencies, and the layout of the PCB. There are two major components to EMI: differential noise and common-mode noise. Differential noise is typically represented in the EMI spectrum below approximately 500kHz while common-mode noise shows up at higher frequencies.

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V+

LINE

NEUTRAL

C16

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Conducted

Figure 34 shows a typical filter used with this LM3448 flyback design. In order to conform to conducted

standards, a fourth order filter is implemented using inductors and "X" rated AC capacitors. If sized properly, this filter design can provide ample attenuation of the switching frequency and lower order harmonics contributing to differential noise. This combination of filter components along with any necessary damping can easily provide a passing conducted EMI signature.

Radiated

Conforming to radiated EMI standards is much more difficult and is completely dependent on the entire system including the enclosure. Reduction of dV/dt on switching edges and PCB layout iterations are frequently necessary. Consult available literature and/or an EMI specialist for help with this. Several iterations of component selection and layout changes may be necessary before passing a specific radiated EMI standard.

Interaction with Dimmers

In general input filters and forward phase dimmers do not work well together. The TRIAC needs a minimum amount of holding current to function. The converter itself is demanding a certain amount of current from the input to provide to its output, and the input filter is providing or taking current depending upon the dV/dt of the capacitors. The best way to deal with this problem is to minimize filter capacitance and increase the regulated hold current until there is enough current to satisfy the dimmer and filter simultaneously.

Design Guide

Figure 34. Input EMI Filter

13.4 Inrush Limiting and Damping

Inrush

With a forward phase dimmer, a very steep rising edge causes a large inrush current every cycle as shown in Figure 35. Series resistance (R5, R6) can be placed between the filter and the TRIAC to limit the effect of this current on the converter and to provide some of the necessary holding current at the same time. This will degrade efficiency but some inrush protection is always necessary in any AC system due to startup. The size of R5 and R6 are best found experimentally as they provide attenuation for the whole system.

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Iin(t)

Potential Misfire

Triac Fires Æ Inrush Spike

Design Calculations

Damper

The inrush spike can also excite a resonance between the input filter of the TRIAC and the input filter of the converter. The associated interaction can cause the current to ring negative, as shown in Figure 35, thereby shutting off the TRIAC. A TRIAC damper can be placed between the dimmer and the EMI filter to absorb some of the ringing energy and reduce the potential for misfires. The damper is also best sized experimentally due to the large variance in TRIAC input filters. Resistors R5 and R6 can also be increased to help dampen the ringing at the expense of some efficiency and power factor performance.

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Figure 35. Inrush Current Spike

14 Design Calculations

The following is a step-by-step procedure with calculations for a 120V, 6.5W non-isolated buck converter design.

14.1 Specifications

V V V P V I

LED

Efficiency,η = 80% fL= 60Hz f

SW(MAX)

Δv Δv

SW FET V SW FET R V VCC= 12V

IN(MAX)

IN(NOM)

IN(MIN)

= 6.5W

OUT

= 36V

OUT

= 181mA

S(MIN)

= 1V

OUT

IN-PK

= 0.8V

f(D4)

= 135VAC = 120VAC

= 85VAC

=75kHz

=13.33µs

= 35V

DS(MAX)

DS-ON

= 600V

= 3.5Ω

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=12V

Z(D7)

R8=49.9kΩ V

=0.7V

GS(Q1)

14.2 Preliminary Calculations

Nominal peak input voltage:

Calculate minimum on-time and verify it's greater than 200ns:

Calculate off-time:

From Figure 29, choose R14=2.0Ω for 6.5W output power with 12 LEDs.

Design Calculations

(29)

(30)

(31)

14.3 FLTR2 AC-LINE Injection

Choose V

INJECT(NOM)

Choose R2=R7=274kΩ Calculate R15:

or,

Calculate maximum FLTR2 pin voltage and verify it is less than 1.25V:

Calculate minimum FLTR2 pin voltage:

=1.0V

(32)

(33)

(34)

(35)

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Design Calculations

14.4 Inductor

Calculate peak inductor currents at the minimum and maximum peak input voltages:

Calculate inductor ripple currents at the minimum and maximum peak input voltages based on 80% of maximum peak inductor currents:

Verify that converter is in CCM operation at the minimum peak input voltage:

Calculate inductor value:

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(36)

(37)

(38)

14.5 COFF Current Source

Choose capacitor C12=470pF. Calculate resistor R16:

Calculate maximum on-time, minimum switching frequency and maximum switching period:

Calculate maximum and minimum duty cycles:

(39)

(40)

(41)

(42)

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14.6 SW FET

Calculate maximum peak SW FET current:

Calculate maximum RMS SW FET current:

Calculate maximum power dissipation:

14.7 Current Limit

Calculate peak inductor current limit:

Power dissipation:

Resulting component choice:

Design Calculations

(43)

(44)

(45)

(46)

(47)

14.8 Re-circulating Diode

Maximum reverse blocking voltage:

Maximum peak diode current:

Maximum RMS diode current:

Maximum power dissipation:

Resulting component choice:

(48)

(49)

(50)

(51)

(52)

(53)

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Design Calculations

14.9 PassFET

Calculate maximum peak voltage:

Calculate current:

Calculate maximum power dissipation:

Resulting component choice:

14.10 Input Capacitance

Minimum capacitance:

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(54)

(55)

(56)

(57)

AC Voltage rating:

DC Voltage rating:

Resulting component choice:

14.11 Output Capacitance

Minimum capacitance:

Voltage rating:

Resulting component choice:

(58)

(59)

(60)

(61)

(62)

(63)

(64)

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R15 C15

DIM

COFF

FLTR2

GND

ISNS

FLTR1

ASNS

BLDR

VCC

GND

LM3448

V+

R22 D8

R14

LED+

LED±

V+

LINE

NEUTRAL

LINE EMI FILTER

COFF

R16

C12

OFF

Current Source

C16

C10

C14

COFF

C13

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15 Evaluation Board Schematic

Evaluation Board Schematic

The LM3448 evaluation board has exposed high voltage 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. Isolating the evaluation board rather than the oscilloscope is highly recommended.

WARNING

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Bill of Materials

16 Bill of Materials

Part ID Description Manufacturer Part Number

C1, C10 CAP CER 47000PF 500V X7R 1210 Johanson Dielectrics 501S41W473KV4E

C2, C6 CAP FILM MKP .015UF 310VAC X2 Vishay/BC Comp BFC233820153

C3 CAP 470UF 50V ELECT PW RADIAL Nichicon UPW1H471MHD C4 DNP DNP DNP

C5, C16 CAP CER .15UF 250V X7R 1210 TDK C3225X7R2E154K

C8 Ceramic, X5R, 16V, 20% MuRata GRM32ER61C476ME15L

C12 Ceramic, X7R, 50V, 10% MuRata GRM188R71H471KA01D

C13, C15 Ceramic, X7R, 16V, 10% MuRata GRM188R71C104KA01D

C14 Ceramic, X7R, 16V, 10% MuRata GRM188R71C474KA88D

D1, D8 DIODE SCHOTTKY 1A 200V PWRDI 123 Diodes Inc. DFLS1200-7

D2 RECT BRIDGE GP 400V 0.5A MINIDIP Diodes Inc. RH04DICT-ND D4 DIODE FAST 1A 300V SMA Fairchild ES1F D7 DIODE ZENER 15V 500MW SOD-123 Fairchild Semi MMSZ5245B

J5, J10 CONN HEADER .312 VERT 2POS TIN Tyco Electronics 1-1318301-2

L1, L2 INDUCTOR 4700UH .13A RADIAL TDK Corp TSL0808RA-472JR13-PF

L3 820uH, Shielded Drum Core, Coilcraft Inc. MSS1038-824KL

Q1 MOSFET N-CH 240V 260MA SOT-89 Infineon Technologies BSS87 L6327 R1, R3 1%, 0.25W Vishay-Dale CRCW1206200kFKEA R2, R7 1%, 0.25W Vishay-Dale CRCW1206274kFKEA

R4 RES 430 OHM 1/2W 5% 2010 SMD Vishay\Dale CRCW2010430RJNEF R5, R6 RES 33 OHM 3W 5% AXIAL TT Electronics/Welwyn ULW3-33RJA1

R8 1%, 0.1W Vishay-Dale CRCW060349K9FKEA

R9 1%, 0.1W Vishay-Dale CRCW060348K7FKEA

R14 RES, 2.00 ohm, 1%, 0.25W, 1206 Vishay-Dale CRCW12062R00FNEA R15 RES, 3.16k ohm, 1%, 0.1W, 0603 Vishay-Dale CRCW06033K16FKEA R16 RES, 226k ohm, 1%, 0.1W, 0603 Vishay-Dale CRCW0603226KFKEA R22 1%, 0.125W Vishay-Dale CRCW080540R2FKEA

TP1, TP2, Terminal, Turret, TH, Double Keystone Electronics 1502-2

TP3, TP4

U1 LM3448 LED Driver Texas Instruments LM3448

www.ti.com

AN-2127 LM3448 A19 Edison Retrofit Evaluation Board SNOA559B–October 2011–Revised May 2013

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17 PCB Layout

NOTE: Spacing between traces and components of this evaluation board are based on high voltage recommendations for designs that will be potted. Users are cautioned to satisfy themselves as to the suitability of this design for the intended end application and take any necessary precautions where high voltage layout and spacing rules must be followed.

PCB Layout

Figure 36. Top Layer

Figure 37. Bottom Layer

SNOA559B–October 2011–Revised May 2013 AN-2127 LM3448 A19 Edison Retrofit Evaluation Board

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Texas Instruments Incorporated AN-2127 User's Guide

Specifications and Main Features

Frequently Asked Questions

User Manual

1 Introduction

2 Key Features

3 Applications

4 Performance Specifications

5 Typical Performance Characteristics

6 EMI Performance

7 Circuit Operation With Forward Phase TRIAC Dimmer

8 Circuit Operation With Reverse Phase Dimmer

9 Thermal Performance

10 LM3448 Device Pin-Out

11 Demo Board Wiring Overview

12 Demo Board Assembly

13 Design Guide

13.1 Buck Converter

13.2 Bias Supplies and Capacitances

13.3 Input Filter

13.4 Inrush Limiting and Damping

14 Design Calculations

14.1 Specifications

14.2 Preliminary Calculations

14.3 FLTR2 AC-LINE Injection

14.4 Inductor

14.5 COFF Current Source

14.6 SW FET

14.7 Current Limit

14.8 Re-circulating Diode

14.9 PassFET

14.10 Input Capacitance

14.11 Output Capacitance

15 Evaluation Board Schematic

16 Bill of Materials

17 PCB Layout