POWERINT DER-92

Design Example Report
Title
0.5W Non-Isolated Buck-Boost Converter
using the LNK302P
Specification
Input: 85-265 VAC
Output: 0.5W, 40mA Constant current
Application
LED Driver
Author
Power Integrations Applications Department
Document
Number
DER-92
Date
August 11, 2005
Revision
1.0
Summary and Features
•
•
•
•
•
•
Low component count (only 9 components required)
Low Cost, light weight, compact solution
No Opto-Coupler required
Open loop operation
High efficiency (~70%)
Meets EN55022 B EMI limits with > 8 dB margin
The products and applications illustrated herein (including circuits external to the products and transformer
construction) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign
patent applications assigned to Power Integrations. A complete list of Power Integrations’ patents may be found at
www.powerint.com.
Power Integrations
5245 Hellyer Avenue, San Jose, CA 95138 USA.
Tel: +1 408 414 9200 Fax: +1 408 414 9201
www.powerint.com
DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
Table Of Contents
1
2
3
4
Introduction .................................................................................................................3
Power Supply Specification ........................................................................................4
Schematic ...................................................................................................................5
Circuit Description.......................................................................................................6
4.1
Input EMI Filtering................................................................................................6
4.2
LinkSwitch-TN .....................................................................................................6
4.3
Output Rectification .............................................................................................6
4.4
Circuit Operation..................................................................................................6
5 PCB Layout.................................................................................................................7
6 Bill Of Materials...........................................................................................................8
7 Spreadsheet ...............................................................................................................9
8 Performance Data.....................................................................................................10
8.1
Efficiency ...........................................................................................................10
9 Waveforms................................................................................................................10
9.1
Drain Voltage and Current, Normal Operation...................................................10
9.2
Output Current, Normal operation......................................................................11
10
Conducted EMI .....................................................................................................12
11
Revision History ....................................................................................................13
Important Note:
Although this board is designed to satisfy safety isolation requirements, the engineering
prototype has not been agency approved. Therefore, all testing should be performed
using an isolation transformer to provide the AC input to the prototype board.
Design Reports contain a power supply design specification, schematic, bill of materials,
and transformer documentation. Performance data and typical operation characteristics
are included. Typically only a single prototype has been built.
Page 2 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
1 Introduction
This document is an engineering report describing a 0.5 W constant current LED driver
power supply utilizing a LNK302P. This power supply is intended as a LED driver that
can be used in emergence exit signs and neon light replacements
The document contains the power supply specification, schematic, bill of materials,
printed circuit layout, and performance data.
Figure 1 - Populated Circuit Board Photograph
Page 3 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
2 Power Supply Specification
Description
Input
Voltage
Frequency
No-load Input Power (230 VAC)
Output
Output Voltage 1
Output Ripple Voltage 1
Output Current 1
Total Output Power
Continuous Output Power
Peak Output Power
Efficiency
Full Load
Symbol
Min
VIN
fLINE
85
47
Typ
50/60
-
Max
Units
Comment
265
64
VAC
Hz
W
2 Wire – no P.E.
VOUT1
VRIPPLE1
IOUT1
13
40
V
mV
mA
POUT
POUT_PEAK
0.5
0.5
W
W
η
70
%
± 5%
20 MHz bandwidth
o
Measured at POUT 25 C
Environmental
Conducted EMI
Meets CISPR22B / EN55022B
Designed to meet IEC950, UL1950
Class II
Safety
Surge
kV
Surge
kV
Ambient Temperature
Page 4 of 14
TAMB
0
25
50
o
C
1.2/50 µs surge, IEC 1000-4-5,
Series Impedance:
Differential Mode: 2 Ω
Common Mode: 12 Ω
100 kHz ring wave, 500 A short
circuit current, differential and
common mode
Free convection, sea level
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
3 Schematic
Figure 2 - Schematic
Page 5 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
4 Circuit Description
This is a very simple circuit, which requires as few as 9 components. An additional input
diode may be placed on the return leg for EMI and surge withstand capability
4.1 Input EMI Filtering
Resistors RF1, RF2 and capacitors C1 and C2 form the EMI filter. C1 C2 and RF2 are
connected to form a low cost resistive π filter and provide excellent differential mode
filtering and also serve as the stable DC bus voltage. Resistor RF1 is a fusible flameproof
type while RF2 can be only flameproof.
4.2 LinkSwitch-TN
LNK302P is used in open loop mode for this circuit. This particular device in the
LinkSwitch-TN family does not have the auto restart feature, and thus when the
feedback pin is left open, the MOSFET switches every cycle until current limit (or duty
cycle limit) is reached.
4.3 Output Rectification
Since this circuit operates strictly in the discontinuous conduction mode (DCM) a 75 nS
recovery time UF4005 diode is used for output rectification. The buck boost topology also
provides benefits of isolating the output from the input in case of Switch failure
4.4 Circuit Operation
This LED driver operates at 66 kHz and energy is provided to the LED’s every switching
cycle. Since the circuit operates in discontinuous mode, a fixed amount of energy is
stored each cycle in L2, then is completely transferred to the load (i.e. the LEDs). The
current in the LED is a triangular waveform, whose peak is determined by the fixed and
well-controlled current limit of the LNK302. The load current is thus independent of line
voltage. As such the need for output filter capacitor is completely eliminated.
Page 6 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
5 PCB Layout
Figure 3 - Printed Circuit Layout
Page 7 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
6 Bill Of Materials
Item Quantity Reference Part
1
2
3
4
5
6
7
8
9
10
Description
Manufacturer
400 V input
2 C1,C2
2.2 uF
UCC
capacitors
0.1 uF, 50 V (ECU- Bypass pin
1 C3
Panasonic
S1H104KBB)
capacitor
Input rectifier Diodes Inc (or
1 D1
1N4007
diode
Generic)
Output rectifier Gen Semiconductor
1 D3
UF4005
diode
(or generic)
AC Input
2 J1,J2
CON1
Generic
connector
Super bright
12 LED1,...12 5mm
OSRAM
White LED's
1 L2
SBC1-102-211
1 mH inductor Tokin
1W, Fusible
1 RF1
8.2 Ohm 1W
and Flameproof VTM
1 RF2
47 Ohm, Flameproof Flameproof
VTM
1 U1
LNK302P
LinkSwitch-TN Power Integrations
Page 8 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
7 Spreadsheet
ACD C_LinkS witch-T N _BuckBoost_042605;
R e v.2.0; Copyright P owe r Inte gra tions 2004 IN P U T
IN FO
OU T P U T
LinkSwitch-T N _BuckBoost_R e v2-0.xls: LinkS witch-T N
D e sign S pre a dshe e t
U N IT
INPUT VARIABLES
Customer
VACMIN
VACMAX
FL
VO
IO
EFFICIENCY (User Estimate)
EFFICIENCY (Calculated Estimate)
CIN
Input Stage Resistance
Ambient Temperature
Input Rectification Type
85
265
50
12.50
0.035
0.75
4.40
8.2
H
Minimum AC Input Voltage
Maximum AC Input Voltage
Line Frequency
Output Voltage
Output Current
Overall Efficiency Estimate (Adjust to match Calculated, or enter
Measured Efficiency)
Calculated % Efficiency Estimate
uF Input Filter Capacitor
ohms Input Stage Resistance, Fuse & Filtering
deg C Operating Ambient Temperature (deg Celcius)
Choose H for Half Wave Rectifier and F for Full Wave Rectification
Volts
Volts
Hertz
Volts
Amps
0.65
4.40
8.2
50
H
DC INPUT VARIABLES
VMIN
VMAX
99.7
374.8
Volts Minimum DC Bus Voltage
Volts Maximum DC Bus Voltage
LINKSWITCH-TN
LINKSWITCH-TN
ILIMIT
ILIMIT_MIN
ILIMIT_MAX
FSMIN
VDS
PLOSS_LNK
LNK302
0.136
0.136
0.146
66000
12.0
0.20
Amps
Amps
Amps
Hertz
Volts
Watts
Selected LinkSwitch-TN
Typical Current Limit
Minimum Current Limit
Maximum Current Limit
Minimum Switching Frequency
Maximum On-State Drain To Source Voltage drop
Estimated LinkSwitch-TN losses
0.70
600
1
75
Volts
Volts
Amps
ns
Freewheeling Diode Forward Voltage Drop
Recommended PIV rating of Freewheeling Diode
Recommended Diode Continuous Current Rating
Recommended Reverse Recovery Time
DIODE
VD
VRR
IF
TRR
Diode Recommendation
UF4005
Suggested Freewheeling Diode
OUTPUT INDUCTOR
L_TYP
989.2
L
1000
L_R
OPERATING MODE
2.0
DCM
KL_TOL
1.15
K_LOSS
ILRMS
0.833
0.06
Page 9 of 14
Required value of Inductance to deliver Output Power (Includes device
uH and inductor tolerances) Choose next higher standard available value
uH Output Inductor, Recommended Standard Value
Ohms DC Resistance of Inductor
Discontinuous Conduction Mode (at VMIN)
Amps Estimated RMS inductor current (at VMAX)
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DER-92
8
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
Performance Data
All measurements performed at room temperature, 60 Hz input frequency.
8.1
Efficiency
Efficiency Vs Line Voltage
80
79
Efficiency
78
77
76
75
74
73
72
71
70
50
100
150
200
250
300
Line Voltage (V)
Figure 4 - Efficiency Vs Line Voltage
9 Waveforms
9.1
Drain Voltage and Current, Normal Operation
Figure 5 - 85 VAC, Full Load.
Upper: IDRAIN, 50 mA / div
Lower: VDRAIN, 50 V, 5 µs / div
Page 10 of 14
Figure 6 - 265 VAC, Full Load
Upper: IDRAIN, 50 mA / div
Lower: VDRAIN, 200 V / div, 2 µs / div
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DER-92
9.2
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
Output Current, Normal operation
Figure 7 - 115VAC
50 ms / div. 5 µs / div
Page 11 of 14
Figure 8 - Start-up Profile, 230 VAC
50 ms / div. 2 µs / div
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
10 Conducted EMI
Figure 9 - Conducted EMI, Maximum Steady State Load, foreground shows 230 VAC, background shows
115 VAC, 60 Hz, and EN55022 B Limits.
Page 12 of 14
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
11 Revision History
Date
Author
August 11, 2005 SK
Page 13 of 14
Revision
1.0
Description & changes
First Draft
Reviewed
AM / VC
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DER-92
0.5W, 40mA, Open Loop LED Driver
August 11, 2005
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information, device or circuit described herein nor does it convey any license under its patent rights or the rights of others. POWER
INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES
INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS.
PATENT INFORMATION
The products and applications illustrated herein (including circuits external to the products and transformer construction) may be
covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power
Integrations. A complete list of Power Integrations’ patents may be found at www.powerint.com.
The PI Logo, T OPSw it c h, T i nySw it c h , Li nk Sw i t c h , DPA-Sw i t c h and Ec oSm ar t are registered trademarks of
Power Integrations. PI Ex pert and PI FA CTS are trademarks of Power Integrations. © Copyright 2005 Power Integrations.
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