Fairchild FEB157-001 User manual

www.fairchildsemi.com
© 2007 Fairchild Semiconductor Page 1 of 17 Rev 1.1 April 2007
FEB157-001 User’s Guide
Offline High Brightness
LED Driver Evaluation Board
Featured Fairchild Product: FAN7554

© 2007 Fairchild Semiconductor Page 2 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Contents
1. Introduction ............................................................................................................................................3
1.1 Product Description ..........................................................................................................................3
1.2 Circuit Description ...........................................................................................................................3
2. Electrical Requirements ............................................................................................................................6
2.1 Input Requirements...........................................................................................................................6
2.2 Output Requirements ........................................................................................................................6
3. Designed Solution ...................................................................................................................................7
3.1 Schematic.......................................................................................................................................7
3.2 Transformer.....................................................................................................................................8
3.3 Bill of Materials ...............................................................................................................................8
3.4 Printed Circuit Board......................................................................................................................10
4. Test Results ...........................................................................................................................................12
4.1 Regulation ....................................................................................................................................12
4.1.1 Line Regulation ..................................................................................................................12
4.2 Efficiency......................................................................................................................................13
4.3 Steady State Operation ..................................................................................................................14
4.4 Start up ........................................................................................................................................15

© 2007 Fairchild Semiconductor Page 3 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
1. Introduction
1.1 Product Description
A high brightness LED evaluation board has been developed using the Fairchild Semiconductor
FAN7554D PWM controller. The board has the capability of driving one, two or three Lumiled,
or similar LEDs. The output current is user selectable at 350mA, 700mA, or 1A. The current is
selectable by inserting or removing jumpers JP1 and JP2 on the evaluation board. The board is
designed to operate over the universal AC line range of 90Vac to 270Vac. A picture of the board is
shown in Figure 1.
Figure 1: Offline High Brightness LED Driver Board
1.2 Circuit Description
The FEB157 evaluation board is an offline flyback converter utilizing the PWM controller,
FAN7554D. Rather than controlling the output voltage, it is designed to control the LED load
current. This is the preferred technique to drive high brightness LEDs. Controlling the LED current
allows for a constant brightness as well as long life of the LEDs. The schematic of the FEB157 is
shown in Figure 3 below.
Referring to Figure 3, the input AC line voltage comes in through J1. Capacitor C1, and common
mode line choke, LF1, form the conducted EMI filter. The dc resistance of LF1 and R1 limit the
inrush current at turn on. Diode bridge BD1 and filter capacitor C2 convert the ac voltage to an
unregulated dc voltage. Resistors R5 and R6 provide the initial startup current for the FAN7554D.
Capacitor C8 off of pin 2 of the FAN7554D provides for soft start in that the pulse width will
gradually increase slowly at turn on thereby decreasing the stress on Q1. Once the converter is up and
running the operating bias voltage will come from the auxiliary winding (pins 4–5) on transformer T1.
The oscillator frequency of the FAN7554D is set by an RC network, R10 and C9. In this board the
frequency is set to 100kHz. However, the FAN7554D can be operated as high as 500kHz.
The FAN7554D is a current mode PWM controller. Current mode operation implies that there are
two control loops. An inside loop that controls the current through the primary winding of the
transformer and an outer loop that controls the output voltage. However, as previously stated, in this
application the outer loop will actually provide feedback information regarding the LED load current
instead of the output voltage.

© 2007 Fairchild Semiconductor Page 4 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Since the output current is being controlled instead of the output voltage, the output voltage will
actually vary with the number of LEDs on the output. The same applies to the auxiliary winding that
provides the bias supply to the FAN7554D. Consequently, the transformer had to be designed to
provide enough bias when powering one LED. Then when powering three LEDs, the bias voltage is
significantly higher. In order to maintain reliable operation, a regulator circuit consisting of R20, ZD1
and Q3 is implemented. This circuit will regulate the voltage to the Vcc pin of the FAN7554 to 18V
when there are multiple LEDs on the output. Please note that this circuit would not be needed in a
conventional application where the number of LEDs on the output is known and fixed. In such an
application, the transformer would then be designed to provide the required Vcc voltage for that
particular number of LEDs.
The FAN7554D will take feedback information from the sense resistor, R12, and from the feedback
pin, pin 1, and generate a PWM signal that is applied to the FET at location Q1. This FET,
FDQ2N80, is a 2A, 800V, N-channel MOSFET in a DPAK package. As with any flyback converter,
energy is stored in the transformer while the FET is on, and released to the secondary when the FET
is turned off. Since no transformer can be constructed with perfect coupling, the network consisting
of resistors R2, R3, R4, diode D1 and capacitor C3 clamp the resulting leakage inductance spike so
that it does not endanger Q1.
The transformer, T1, is constructed on an EFD20 core/bobbin. The energy stored in the transformer
during the on time of Q1 is delivered to the secondary during the off time of Q1. Diode D4, and
C11 rectify and filter the resulting secondary waveform to form a dc voltage. Inductor L1 and
capacitor C12 provide additional attenuation of any residual switching spikes on the output voltage.
Connector J2 is a Tyco six position connector (p/n 535676-5) that will mate with Future Electronics
LED “Emitter” boards to carry the dc power to the LEDs. A picture of a three LED assembly is shown
in Figure 2.
Figure 2: Offline LED Driver and LED Assembly
As previously mentioned, when driving high brightness LEDs the objective is to control the LED
current. There are different ways of controlling the current. In this evaluation board a method utilizing
sense resistors and an NPN transistor is used. Referring to the schematic in Figure 3, resistors R14,
R15, and R16 are the resistors that sense the return current from the LED load. Jumpers JP1 and JP2
allow the selection of the output current. Table 1 describes the jumper status for particular output
currents.

© 2007 Fairchild Semiconductor Page 5 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Table 1: Jumper JP1/JP2 Status and LED Current
Refer to the schematic in Figure 3. As the LED current returns back to the power supply, it develops a
voltage across the sense resistor(s). Once this voltage reaches the base-emitter junction voltage of the
NPN Q2, typically about 650mV, the transistor will conduct collector current. This current also flows
through the photodiode inside the optocoupler, IC2. The optocoupler will transfer this feedback
information optically across the primary-secondary boundary to the primary side of the supply
thereby maintaining the necessary isolation. Thermistor RTH1, is a negative temperature coefficient
device and compensates for changes in base-emitter voltage due to temperature change.
LED Current JP1 Status JP2 Status
350mA Out Out
700mA In Out
1A In In

© 2007 Fairchild Semiconductor Page 6 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
2. Electrical Requirements
2.1 Input Requirements
Voltage range: 90Vrms to 270Vrms
Frequency: 47Hz to 63Hz
2.2 Output Requirements
The FEB157 board will power one, two, or three high brightness LEDs (Lumiled or similar) at user
selectable load currents of 350mA, 700mA, or 1A.

© 2007 Fairchild Semiconductor Page 7 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
3. Designed Solution
3.1 Schematic
Figure 3: Schematic of the FEB157 Offline High Brightness LED Driver Board
F1
1A, 250V
C1
0.1µF
R1
5.6Ω
1W
C2
47µF
450V
R7
22Ω
0805
Q1
FQD2N80
R10
10kΩ
1%
0603
Vref Vcc Drive GND
87 65
123 4
FB S/S IS Rt/Ct
C8
1µF
C7
0.1µF
C10
470pF
C9
1800pF
D3
BAS21
R9
4.7Ω
0805
C4
47µF
50VZD1
18 V
C5
0.1µF
R12
1.2Ω
2512
R11
1kΩ
0805
D1
RS1M
C3
1000pF
1kV
R2
22kΩ
2010
R3
22kΩ
2010
R4
10Ω
1206
C6
0.01µF
R5
150kΩ
2010
R6
150kΩ
2010
R8
10kΩ
0603
D2
Prov. for MMBD4148
D4
SS39
C11
1000µF
16V
L1
2.2µH
C12
47µF
50V R14
1.8Ω, 2010
R15
2Ω, 2010
R16
1.8Ω
2010
Q2
MMBT2222AK
RTH1
10kΩ
0805
R17
510Ω
0603
C13
2200pF
Y-cap
R18
100Ω
0603
BD1
DF10S
FAN7554D IC1
IC2
FOD817A
IC2
FOD817A
LF1
R13
Prov. for 2512
3
2
1
Lm = 610µH
T1
EFD20 Core/Bobbin
4
5
8
1
2
5
6
J2
JP1
JP2
R19
Prov. for 2010
C14
Prov. for 0805
ZD2
Prov. for SOD-123
Q3
MMBT2222A
R20
1kΩ
2010 TP2
TP1
TP3
TP4
TP5
TP6
2
3
C15
100pF
R21
47Ω
2010

© 2007 Fairchild Semiconductor Page 8 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
3.2 Transformer
3.3 Bill of Materials
Sch Ref Vendor Part Number Description
BD1 Fairchild DF10S 1.5A, 1000 V Bridge
C1 NIC Components or Equivalent NPX104M275VX2M 0.1µF, X2 cap
C2 NIC Components NREH470M450V18X36F 47µF, 450V
UCC ESMH451ESN470MN25S 47µF, 450V
C3 TDK C4520X7R3A102KT 1000 pF, 1kV, SMD
C4 NIC Components or Equivalent NACK470M50V6.3X8TR 47µF, 50V, SMD
C5 NIC Components or Equivalent NMC0603X7R104K50TRP 0.1µF, 50V, 0603
C6 NIC Components or Equivalent NMC0603X7R103K50TRP 0.01µF, 50V, 0603
C7 NIC Components or Equivalent NMC0603X7R104K50TRP 0.1µF, 50V, 0603
C8 NIC Components or Equivalent NMC0603X7R105K16TRP 1.0µF, 16V, 0603
C9 NIC Components or Equivalent NMC0603NPO182F25TRP 1800 pF, 25V, 0603, NPO
C10 NIC Components or Equivalent NMC0603X7R471K50TRP 470 pF, 50V, 0603
C11 NIC Components or Equivalent NRSJ102M16V10X16TB 1000µF, 16V, Leaded
C12 NIC Components or Equivalent NACK470M50V6.3X8TR 47µF, 50V, SMD
C13 Panasonic ECK-NVS222ME 2200pF, Y-rated cap
C14 Prov. for 0805
C15 TDK C4520CH3F101K 100 pF, 3kV, SMD
1/2 Primary - 36 T
Secondary - 10T
1/2 Primary - 36 T
Vcc 25 T
1
2
3
1/2 Pri - 36 T
1/2 Pri - 36 T
Vcc - 25 T
Output - 10 T
Core = EFD20
Bobbin = 10 pin; SMD; Horizontal
4
5
6
8
Required Components Schematic Winding Stackup
Electrical Specifications
Inductance
Leakage
Pin Spec. Remarks
1 - 3 537.0 - 656.0 uH
1 - 3
100 kHz, 0.10 Vrms
All other windings shorted

© 2007 Fairchild Semiconductor Page 9 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Conn1 Phoenix Contact 1729018 2 position terminal block
Conn2 Tyco 535676-5 6 position connector
D1 Fairchild RS1M 1A, 1000V, SMA
D2 Fairchild Prov. for MMBD4148
D3 Fairchild BAS21 0.2A, 250V, SOT-23
D4 Fairchild SS39 3A, 90V, SMC
F1 Littlefuse 3721100 1A, 250V, Slo-Blo
IC1 Fairchild FAN7554D PWM Controller, SO-8
IC2 Fairchild FOD817A Optocoupler
JP1 Sullins PRPN021PAEN-RC 2 pin header (2mm)
JP2 Sullins PRPN021PAEN-RC 2 pin header (2mm)
JP1 Sullins STN02SYBN-RC 2 pin shunt
JP2 Sullins STN02SYBN-RC 2 pin shunt
L1 Coilcraft DO1608C-222 2.2µH
LF1 Sumida UU9LFBNP-B322 3.2mH
Q1 Fairchild FQD2N80 2A, 800V, N-channel, DPAK
Q2 Fairchild MMBT2222AK 0.6A, 40V, NPN
Q3 Fairchild MMBT2222AK 0.6A, 40V, NPN
R1 NIC Components or Equivalent NCF100J5R6TR 5.6Ω, 1 W
R2 NIC Components or Equivalent NRC50J223TR 22kΩ, 1/2 W, 2010
R3 NIC Components or Equivalent NRC50J223TR 22kΩ, 1/2 W, 2010
R4 NIC Components or Equivalent NRC12J100TR 10Ω, 1/4 W, 1206
R5 NIC Components or Equivalent NRC50J154TR 150kΩ, 1/2 W, 2010
R6 NIC Components or Equivalent NRC50J154TR 150kΩ, 1/2 W, 2010
R7 NIC Components or Equivalent NRC10J220TR 22Ω, 1/8 W, 0805
R8 NIC Components or Equivalent NRC06J103TR 10kΩ, 1/10 W, 0603
R9 NIC Components or Equivalent NRC10J4R7TR 4.7Ω, 1/8 W, 0805
R10 NIC Components or Equivalent NRC06F1002TR 10kΩ, 1/10 W, 1%, 0603
R11 NIC Components or Equivalent NRC10J102TR 1kΩ, 1/8 W, 0805
R12 NIC Components or Equivalent NRC100J1R2TR 1.2Ω, 1 W, 2512
R13 Prov. for 2512
R14 NIC Components or Equivalent NRC50J1R8TR 1.8Ω, 3/4 W, 2010
R15 NIC Components or Equivalent NRC50J2R0TR 2.0Ω, 3/4 W, 2010
R16 NIC Components or Equivalent NRC50J1R8TR 1.8Ω, 3/4 W, 2010
3.3 Bill of Materials (Continued)
Sch Ref Vendor Part Number Description

© 2007 Fairchild Semiconductor Page 10 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
3.4 Printed Circuit Board
The PCB is a double sided board made of FR4 with 1oz copper.
Figure 4: Silkscreen/Component Placement of PCB Layout
R17 NIC Components or Equivalent NRC06J511TR 510Ω, 1/10 W, 0603
R18 NIC Components or Equivalent NRC06J101TR 100Ω, 1/10 W, 0603
R19 Prov. for 2010
R20 NIC Components or Equivalent NRC50J102TR 1kΩ, 3/4 W, 2010
R21 NIC Components or Equivalent NRC50J470TR 47Ω, 3/4 W, 2010
RTH1 NIC Components or Equivalent NCT08AJ104334TR 10kΩ, NTC Thermistor, Beta = 3340
T1 Cooper CTX0117893 EFD20 Core/Bobbin Transformer
TP1 Keystone 5002 PC Test Point-White
TP2 Keystone 5001 PC Test Point-Black
TP3 Keystone 5000 PC Test Point-Red
TP4 Keystone 5000 PC Test Point-Red
TP5 Keystone 5001 PC Test Point-Black
TP6 Keystone 5003 PC Test Point-Orange
ZD1 Fairchild MMSZ5248B 18V, 1/2W, SOD-123
ZD2 Prov. for SOD-123
3.3 Bill of Materials (Continued)
Sch Ref Vendor Part Number Description

© 2007 Fairchild Semiconductor Page 11 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Figure 5: Silkscreen/Component Placement of Top Side Layer
Figure 6: Silkscreen/Component Placement of Bottom Side Layer

© 2007 Fairchild Semiconductor Page 12 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
4. Test Results
4.1 Regulation
4.1.1 Line Regulation
This graph illustrates the regulation of the output current over line voltage for the three possible
settings, 350mA, 700mA, and 1A.
Figure 7: LED Current vs. Line Voltage
Input Voltage (Vac)
LED Current (mA)
1 LED
2 LEDs
3 LEDs
0
200
400
600
800
1000
1200
90 120 270

© 2007 Fairchild Semiconductor Page 13 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
4.2 Efficiency
The efficiency data shown is for the converter with a load of one, two and three LEDs driven at 1A.
Figure 8: Converter Efficiency Data Plotted Against Increasing Line Input
for LED Current of 1A.
0
10
20
30
40
50
60
70
80
90
90 120 270
Input Voltage (V)
Efficiency (%)
1 LED @ 1 A
2 LEDs @ 1
A
3 LEDs @ 1
A

© 2007 Fairchild Semiconductor Page 14 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
4.3 Steady State Operation
Figure 9: Steady State Waveforms at 90Vac with Three LEDs at 1A
Figure 10: Steady State Waveforms at 270Vac with One LED at 350mA

© 2007 Fairchild Semiconductor Page 15 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
4.4 Start up
The startup profile is captured at 90Vac and 270Vac with a load of three LEDs operating at a current
of 1A.
Figure 11: Startup Profile at 90 Vac with Three LEDs at 1A
Figure 12: Startup Profile at 270Vac with Three LEDs at 1A

© 2007 Fairchild Semiconductor Page 16 of 17 Rev 1.1 April 2007
www.fairchildsemi.com
Warning and Disclaimer:
This Evaluation Board may employ high voltages so appropriate safety precautions should be used
when operating this board. Replace components on the Evaluation Board only with those parts shown
on the parts list in the User's Guide. Contact an authorized Fairchild representative with any
questions.
The Evaluation Board is for demonstration purposes only and neither the Board nor this User's Guide
constitute a sales contract or create any kind of warranty, whether express or implied, as to the
applications or products involved. Fairchild warranties that its products will meet Fairchild's published
specifications but does not guarantee that its products will work in any specific application. Fairchild
reserves the right to make changes without notice to any products described herein to improve
reliability, function or design. Either the applicable sales contract signed by Fairchild and Buyer, or if
no contract exists Fairchild's Standard Terms and Conditions on the back of Fairchild invoices, govern
the terms of sale of the products described herein.

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