RDR-131

Title Reference Design Report for 3 W NonIsolated Constant Current LED Driver Using LNK306DN Specification 85–265 VAC Input, 10 V, 300 mA Output Application Author Document Number Date Revision LED Lighting / Bulb Retrofit Power Integrations Applications Department RDR-131 March 7, 2007 1.1 Summary and Features • • • • • • • Extremely small form factor, fits within GU10 lamp base Operates over the universal input voltage range (85 – 265 VAC) Meets EN55022 B conducted EMI requirements Drives LEDs in constant current (CC) mode Built-in, output overvoltage protection when unloaded • Allows supply to be tested without the load connected Low parts count, low-cost solution: only 25 components Non-isolated buck converter configuration allows use of off-the-shelf inductors (does not require a custom transformer) 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 RDR-131 LED Driver – LNK306DN 7-Mar-07 Table of Contents 1 2 3 4 Introduction...............................................................................................................3 Power Supply Specification ......................................................................................5 Circuit Diagram.........................................................................................................6 Circuit Description ....................................................................................................7 4.1 Configuration and Assembly Details..................................................................7 4.2 AC Input Rectification ........................................................................................7 4.3 LinkSwitch-TN ...................................................................................................7 4.4 Output Feedback...............................................................................................7 5 Bill of Materials .......................................................................................................10 5.1 Filter Board Bill of Materials.............................................................................10 5.2 Converter Board Bill of Materials.....................................................................11 6 PI Xls Design Spreadsheet.....................................................................................12 7 Performance ...........................................................................................................14 7.1 Efficiency .........................................................................................................14 7.2 Output Current Regulation Vs. Line Voltage....................................................15 7.3 Output VI Characteristic ..................................................................................15 8 Waveforms .............................................................................................................16 8.1 Drain Voltage and Current, Normal Operation.................................................16 8.2 Output Current and Voltage.............................................................................16 8.3 Drain Current and Bulk Capacitor Voltage.......................................................17 8.4 Startup Drain Current and Bulk Capacitor Voltage ..........................................17 8.5 Startup Output Voltage and Current ................................................................18 8.6 Fault Conditions ..............................................................................................18 9 Thermal Measurements..........................................................................................19 10 Conducted EMI.......................................................................................................20 10.1 Competitive Product EMI.................................................................................21 11 Revision History......................................................................................................22 Important Note: This board has no safety isolation. Therefore, all testing should be performed using an isolation transformer to provide the AC input to the prototype board. Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 2 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN 1 Introduction This engineering report describes an LED driver power supply that uses a member of the LinkSwitch-TN family of devices, the LNK306DN. The circuit regulates its load current to 300 mA while developing about 10 V across three series HB-LEDs. The design provides no safety isolation between the AC input and DC output. Therefore the enclosure must be designed to provide isolation. The report contains the power supply specification, a circuit diagram, a complete bill of materials, the PI Xls spreadsheet results for the design, the printed circuit board layouts, and performance data. Figure 1 – Photographs of (Top and Side views) Populated Circuit Board Assembly. Page 3 of 24 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com RDR-131 LED Driver – LNK306DN 7-Mar-07 Figure 2 – Mechanical Positioning of the Power Supply Assembly Inside the GU10 Bulb Socket Base. Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 4 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN 2 Power Supply Specification Description Input Voltage Frequency No-load Input Power (230 VAC) Output Output Voltage 1 Output Current 1 Total Output Power Continuous Output Power Efficiency Environmental Conducted EMI Safety Ambient Temperature TAMB Meets EN55022B/CISPR22B No input to output isolation 0 40 o Symbol VIN fLINE Min 85 47 Typ Max 265 64 - Units VAC Hz W V A Comment 2 Wire – no P.E. Not applicable ± 10% at 25 C o 50/60 VOUT1 IOUT1 POUT η 10 0.3 3 62 W % Measured at POUT (3 W), 25 C o C Free convection, sea level Page 5 of 24 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com RDR-131 LED Driver – LNK306DN 7-Mar-07 3 Circuit Diagram Figure 3a – Circuit Diagram of Filter Board. Figure 3b – Circuit Diagram of Converter Board. Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 6 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN 4 Circuit Description 4.1 Configuration and Assembly Details The power supply is configured as a non-isolated buck converter. Since it must fit in a GU10 lamp socket base, the supply was split into 2 interconnected boards. A Faraday shield (the third board) was sandwiched between the input rectification/EMI filter (bottom) board and the converter (top) board. The shield board is electrically connected to the converter board. This was necessary to meet the conducted EMI requirements. The shield consists of a single-sided, copper-clad PCB that is the same size as the input rectification/EMI filter board. 4.2 AC Input Rectification A 10 Ω fusible resistor (RF1) will act as a fuse if a catastrophic failure occurs. The input voltage and current are rectified by a bridge rectifier (BR1) and smoothed by a pi filter circuit (C1, L1 and C2). The pi filter and RF1 also help attenuate the differential mode conducted EMI that is generated by the switching of the buck converter. 4.3 LinkSwitch-TN The PI Xls spreadsheet tool was used to design this converter. When powering the designated LED load, the converter operates in the continuous conduction mode (CCM). The buck converter stage consists of the integrated MOSFET switch within the LNK306DN (U1), a freewheeling diode (D3), an output inductor (L2) and an output capacitor (C3). An Ultrafast MURS160T3 was chosen for the freewheeling diode to minimize the amplitude of the MOSFET turn-on spike. The remaining components are involved in sensing the normal-load output current and the no-load output voltage and conveying that information back to the FEEDBACK (FB) pin of the LNK306DN. 4.4 Output Feedback The LinkSwitch-TN uses On/Off control to regulate the output of the supply. During each enabled switching cycle the drain current ramps to a fixed internal current limit level. When current into the FEEDBACK (FB) pin exceeds 49 µA the next switching is disabled. By adjusting the number of enabled to disabled cycles the amount of energy delivered to the output can be varied to maintain regulation. The 49 µA threshold is specified at a FB pin voltage of 1.65 V allowing this pin to be used as a voltage reference. In this design both current and voltage feedback is used. Current feedback limits the LED current during normal operation while voltage feedback limits the output voltage should the LED load be disconnected, for example during production testing. During the off time of U1, the voltage that appears across C2 is equal to the output voltage less a diode drop. In this design two 250 V rated diodes, D1 and D2, were used for space reasons, however a single 600 V diode could be used (in this case the voltage across C2 would be equal to the output voltage). Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 7 of 24 RDR-131 LED Driver – LNK306DN 7-Mar-07 This voltage is divided by R7 and R1 so the voltage at the FB pin is 1.65 V when the output voltage reaches ~12 V. Due to the interaction with the current sense circuit and the small output capacitor value the actual peak no-load voltage is limited to ~18 V. Current feedback is provided by sensing the voltage drop across R8 and R10, which is filtered by R4 and C6. Once the voltage drop exceeds the VBE of Q1, both Q1 and Q2 turn on, feeding additional current into the FB pin of U1 from C2. By adjusting the ratio of enabled to disabled cycles the average output current is controlled. As the VBE of Q1 varies with temperature the circuit exhibits a negative output current temperature coefficient. Resistor R11 provides a minimum load to ensure correct operation at zero load. This relatively complicated current sense can be simplified by using the FB pin directly to sense the voltage drop across the sense resistors. However as the FB pin has a voltage of 1.65 V this resulted in unacceptable dissipation (0.3 A x 1.65 V = 0.5 W) inside the GU10 enclosure. However in less thermally challenging designs this approach may be used. Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 8 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN Filter Board Converter Board (Bottom and Top Side) Figure 4 – Printed Circuit Board Layouts. Page 9 of 24 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com RDR-131 LED Driver – LNK306DN 7-Mar-07 5 Bill of Materials The BOM for each board is presented separately. 5.1 Item 1 2 3 4 5 6 Filter Board Bill of Materials Qty 1 2 3 0.08 Ft. 1 1 0.17 Ft. 0.07 Ft. 0.03 Ft. 0.07 Ft. 0.15 Ft. 0.06 Ft. Ref Des BR1 C1 C2 Value MB6S 4.7 µF Description Mfg Part Number Mfg Comment 600 V, 0.5 A, Bridge MB6S Vishay Rectifier, SMD, TO-269AA 4.7 µF, 380 V, Electrolytic, XX380VB4R7M8 Nippon X11LL Chemi-Con (8 x 11.5) N/A 298 SBC1-102-211 CRF253-4 10R N/A Alpha Tokin Vitrohm Solder wire in J1 Location (apply teflon tubing (SW1) over wire) Solder wire in J2 location (apply teflon tubing (SW2) over wire) Solder wire in J3 location (teflon tubing not required) Place over JP1 Place over W1 Place over W2 PCB PCB Terminal Hole, 22 J1 J2 J3 Terminal AWG 22 AWG Wire Jumper, NonJP1 insulated, 22 AWG, 0.6 in 1000 µH, 0.21 A, 5.5 x L1 1000 µH 10.5 mm 10 Ω, 2.5 W, RF1 10 Ω Fusible/Flame Proof Wire Wound W1 Wire Jumper, Noninsulated, 22 AWG Wire Jumper, Noninsulated, 22 AWG Wire Jumper, Noninsulated, 22 AWG 7 298 Alpha 8 W2 298 Alpha 9 10 11 12 W3 SJP1 SW1 SW2 298 Alpha Alpha Alpha Alpha Teflon Tubing for 22 AWG TFT-200-22 wire Teflon Tubing for 22 AWG TFT-200-22 wire Teflon Tubing for 22 AWG TFT-200-22 wire Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 10 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN 5.2 Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Converter Board Bill of Materials Qty Ref Des 3 1 2 1 2 1 1 1 2 3 1 1 1 1 1 Value Description 100 nF 25 V, Ceramic, X7R, 0603 2.2 uF, 25 V, Ceramic, X7R, 1206 Mfg Part Number ECJ-1VB1E104K ECJ-3YB1E225K Mfg Panasonic Panasonic Diode Inc. On Semi N/A ICE Components Diodes Inc Diodes Inc Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic Power Integrations Alpha Solder wire in J2 Location (teflon tubing is not required) Comment C1 C2 C6 100 nF C3 D1 D2 D3 J1 J2 L2 Q1 Q2 R1 R9 2.2 µF BAV21WS-7-F MURS160T3 PCB Terminal 22 AWG 1000 µH MMST3904 MMST3906 4.7 kΩ 250 V, 0.2 A, Fast BAV21WS-7-F Switching, 50 ns, SOD-323 600 V, 1 A, Ultrafast Recovery, 35 ns, SMB Case PCB Terminal Hole, 22 AWG 1000 µH, 0.3 A NPN, Small Signal BJT, 40 V, 0.2 A, SOT-323 PNP, Small Signal BJT, 40 V, 0.2 A, SOT-323 4.7 kΩ, 5%, 1/10 W, Metal Film, 0603 10 kΩ, 5%, 1/10 W, Metal Film, 0603 30 kΩ, 5%, 1/10 W, Metal Film, 0603 2 Ω, 5%, 1/4 W, Metal Film, 1206 12 Ω, 5%, 1/10 W, Metal Film, 0603 1 kΩ, 5%, 1/4 W, Metal Film, 1206 LinkSwitch-TN, LNK306D, SO-8 Wire jumper, non insulated, 22 AWG MURS160T3G N/A L03316-102-RM MMST3904-7-F MMST3906-7 ERJ-3GEYJ472V ERJ-3GEYJ103V ERJ-3GEYJ303V ERJ-8GEYJ2R0V ERJ-3GEYJ120V ERJ-8GEYJ102V LNK306D R3 R4 R6 10 kΩ R7 R8 R10 R11 U1 30 kΩ 2Ω 12 Ω 1 kΩ LNK306D 16 0.17 W2 Ft. 298 17 18 1 1 J3 J4 CON1 CON1 Test Point, RED, Miniature 5000 THRU-HOLE MOUNT Test Point, BLK, Miniature 5001 THRU-HOLE MOUNT Keystone Keystone Page 11 of 24 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com RDR-131 LED Driver – LNK306DN 7-Mar-07 6 PI Xls Design Spreadsheet INPUT INFO OUTPUT UNIT LinkSwitch-TN_Rev_2-2.xls: LinkSwitch-TN Design Spreadsheet ACDC_LinkSwitchTN_030906; Rev.2.2; Copyright Power Integrations 2006 INPUT VARIABLES VACMIN VACMAX FL VO IO EFFICIENCY (User Estimate) EFFICIENCY (Calculated Estimate) CIN Input Stage Resistance Ambient Temperature Switching Topology Input Rectification Type 85 265 50 12.00 0.330 0.72 0.78 9.40 Volts Volts Hertz Volts Amps Customer 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 F 9.40 uF Input Filter Capacitor 0.00 ohms Input Stage Resistance, Fuse & Filtering 50 deg Operating Ambient Temperature (deg Celsius) C Buck Type of Switching topology F Choose H for Half Wave Rectifier and F for Full Wave Rectification DC INPUT VARIABLES VMIN VMAX LinkSwitch-TN LinkSwitch-TN ILIMIT ILIMIT_MIN ILIMIT_MAX FSMIN VDS PLOSS_LNK DIODE VD VRR IF TRR Diode Recommendation OUTPUT INDUCTOR L_TYP 79.1 Volts Minimum DC Bus Voltage 374.8 Volts Maximum DC Bus Voltage Auto LNK306 0.482 Amps 0.450 Amps 0.515 Amps 62000 Hertz 6.2 Volts 0.51 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 Volts 600 Volts 1 Amps 35 ns BYV26C Freewheeling Diode Forward Voltage Drop Recommended PIV rating of Freewheeling Diode Recommended Diode Continuous Current Rating Recommended Reverse Recovery Time Suggested Freewheeling Diode 941.6 L L_R OPERATING MODE KL_TOL K_LOSS ILRMS 1000 2.0 CCM 1.15 0.813 0.33 Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com uH Required value of Inductance to deliver Output Power (Includes device and inductor tolerances) Choose next higher standard available value uH Output Inductor, Recommended Standard Value Ohm DC Resistance of Inductor s Continuous Conduction Mode (at VMIN) Inductor tolerance Factor. Accounts for basic (10% 20%) Manufacturing Tolerances 1.1 < KL_TOL < 1.2 See AN-37 for detailed explanation Loss factor. Accounts for "off-state" power loss to be supplied by inductor Calculated efficiency < K_LOSS < 1. See AN-37 for detailed explanation Amps Estimated RMS inductor current (at VMAX) Page 12 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN OUTPUT CAPACITOR DELTA_V MAX_ESR I RIPPLE FEEDBACK COMPONENTS RBIAS RFB CFB C_SOFT_START 0.12 Volts Target Output Voltage Ripple 467 m- Maximum Capacitor ESR (milli-Ohms) Ohm s 0.26 Amps Output Capacitor Ripple current kOhm s 11.86 kOhm s 10 uF 39092 uF 2.00 Bias Resistor. Use closest standard 1% value Feedback Resistor. Use closest standard 1% value Feedback Capacitor If the output Voltage is greater than 12 V, or total output and system capacitance is greater than 100 uF, a soft start capacitor between 1uF and 10 uF is recommended. See AN-37 for details Note: The feedback components in the spreadsheet were not used on the power supply because a higher impedance was required by the CC feedback circuit. Page 13 of 24 Power Integrations Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com RDR-131 LED Driver – LNK306DN 7-Mar-07 7 Performance 7.1 Efficiency Efficiency measured at different line voltages are collected in the table below. VAC IN Efficiency 85 0.642 115 0.639 220 0.588 265 0.562 Table 1: Efficiency data measured at different AC input line voltages. 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 70 120 170 220 270 Efficienc y VAC Figure 5 – Efficiency vs. Input Voltage, Room Temperature. Power Integrations, Inc. Tel: +1 408 414 9200 Fax: +1 408 414 9201 www.powerint.com Page 14 of 24 7-Mar-07 RDR-131 LED Driver – LNK306DN 7.2 Output Current Regulation Vs. Line Voltage 400 380 360 Output Current (mA 340 320 300 280 260 240 220 2 00 50 100 150 200 250 300 Input Voltage (VAC) Figure 6 – Output Current vs. Input Voltage (stabilized, room temperature operation*). 7.3 Output VI Characteristic 16 14 12 85 VAC 265VAC Output Voltage 10 8 6 4 2 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Output Current (mA) Figure 7 – Output Current vs. Output Voltage. Note: When driving a LED load operation at