DI-74 LNK304PN EN55022 AN-37 BZX79C18 UF4005 1N4007 PI-3846-010208

LinkSwitch-TN ® 1.25 W Non-Isolated Constant Current LED Driver Application Device Power Output Input Voltage Output Voltage

DI-74 DI-74 Design Idea LinkSwitch-TN ® 1.25 W Non-Isolated Constant Current LED Driver Application Device Power Output Input Voltage Output Voltage Topology LED Driver LNK304PN LNK304PN 1.25 W 85 265 VAC 12.5 V, 100 mA Buck-Boost Design Highlights · Universal AC input range single design worldwide · Accurate and stable constant current output · Small size and weight · Low cost, low component count solution replaces passive capacitor or resistor droppers · Fail safe topology protects load · High efficiency (>60% at 85 VAC) · Scalable output power using larger LinkSwitch-TN devices · Meets EN55022 EN55022 B EMI limits LinkSwitch-TN uses ON/OFF control to regulate the output current. When the current into the FEEDBACK (FB) pin exceeds 49 A, MOSFET switching is disabled for the next switching cycle. The 49 A threshold is specified at a pin voltage of 1.65 V (±7%), allowing it to be used as a reference. Operation Using the Buck-Boost topology, the circuit shown in Figure 1 generates a non-isolated constant current (CC) output for driving LEDs. Typical uses include night-lights, neon sign replacements, emergency exit signs or any application utilizing LEDs for lighting. The voltage developed across R3, which is averaged by C4, represents the output current. When this voltage exceeds 2 V, the voltage on the FB pin, via divider of R1 and R2, exceeds 1.65 V and >49 A current is fed into the pin. The 2 V across R3 sets an output current of 100 mA, or 25 mA for each string of LEDs. If the load is disconnected or the output is shorted, no feedback is provided and LinkSwitch-TN enters auto-restart (5% on time). To prevent a high output voltage under no load the optional voltage feedback circuit can be included by adding VR1 and D4. The voltage of VR1 is selected to be above the normal output voltage. The AC input is rectified and filtered by D1, D2, C1, C2, RF1, and RF2. Two diodes improve both line surge withstand (2 kV) and conducted EMI. Resistor RF1 should be a fusible flameproof type, whereas RF2 can be flameproof only. Select the value of L1 following AN-37 AN-37, LinkSwitch-TN Design Guide or using the PIXls design spreadsheet. Enter the output voltage as the voltage of the LED string and the output current as the total combined LED current. VR1 R2 BZX79C18 BZX79C18 D4 300 18 V, 500 mW UF4005 UF4005 1% RF1 D1 8.2 , 1 W 1N4007 1N4007 Fusible RF2 47 , 0.5 W Flame Proof FB D BP S LinkSwitch-TN U1 LNK304PN LNK304PN 85-265 VAC C1 4.7 uF 400 V C2 4.7 uF 400 V R1 2 k 1% C3 0.1 uF 50 V L1 1.2 mH 220 mA R3 20 0.5 W 1% C4 47 uF 10 V C5 1 uF, 50 V low ESR LED 1-20 25 mA per String D3 UF4005 UF4005 1 A, 600 V Ultrafast 12.5 V, 100 mA D2 1N4007 1N4007 PI-3846-010208 PI-3846-010208 Figure 1. www.powerint.com Schematic of a 1.25 W, 12.5 V, 100 mA Constant Current LED Driver, Using a Non-Isolated Buck-Boost Topology. January 2008 PI-3847-020904 PI-3847-020904 80 70 60 QP 50 AV Quasi-Peak 40 dBV 30 20 Average 10 0 -10 -20 0.15 1.0 10.0 100.0 MHz Figure 2. Conducted EMI Plot of the Schematic Shown in Figure 1 for 3 Strings of 4 LED's (10 V, 66.6 mA). PI-3848-021304 PI-3848-021304 25 Output Voltage (V) Key Design Points · The output is not safety isolated from the input. · The circuit shown in Figure 1 has a total output current tolerance of ±12% (including t of 50 °C). · To prevent noise coupling and to decrease EMI, place the input filter components physically away from the source node of the LinkSwitch-TN and L1 inductor. The DC input filter capacitors C1 and C2 can be placed, as a barrier, between the AC input and U1/L1. · Select C4 so that C4 20 · (15 ms / R3), to provide adequate filtering of the current sense voltage. Values above 50 · (15 ms / R3) will yield little improvement in CC linearity. · Select C5 based on the acceptable peak current through the LEDs. Larger values of capacitance reduce peak LED current. Typical values are 100 nF to 100 F, low ESR. With no capacitor the peak output current is equal to the internal current limit of U1. · With the values of R1 and R2 shown, the value of R3 is calculated by R3 = 2 V / IO. · The supply's total required output current is determined by the number of LED strings in the load, and is limited by the value of L1 and the current limit of U1. For this circuit, the load should be 100 mA and 1.25 W total. AC Input = 85 V AC Input = 265 V 20 15 10 5 0 0 20 40 60 80 100 120 Output Current (mA) Figure 3. VI Characteristic of the Schematic Shown in Figure 1. Power Integrations 5245 Hellyer Avenue San Jose, CA 95138, USA. Main: +1 408-414-9200 Customer Service Phone: +1-408-414-9665 Fax: +1-408-414-9765 Email: usasales@powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY 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. The products and applications illustrated herein (transformer construction and circuits external to the products) 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 grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm. 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