AL8807EV4 USER GUIDE Performance Introduction • • • • This evaluation circuit demonstrates the AL8807 High Efficiency 30V 1.5A Buck LED Driver operating in a circuit providing 1.1A LED current in MR16 form intended to drive 1 to 3 high brightness LEDs in series with a total load voltage drop up to 10V. The circuit includes a 470µF reservoir capacitor to prevent flicker for 50Hz or 60Hz AC input power. EMC filtering is included to meet international standards including the radiated emission requirements of EN55015 and EN55022 Class B. • 12VDC and 12VAC input 1.1A LED current Drives 1 to 3 LEDs in series 2% current regulation 9V to 30VDC (with 2 LEDs) Ambient temperature range -40°C to +105°C Ordering Information Order Number AL8807EV4 The switching frequency is approximately 440kHz when driving 2 Osram Dragon Diamond LEDs. The construction uses a double-sided FR4 printed circuit board, 17 x 20 x 0.8 mm with 2oz/sq ft copper (70µm). Components are mounted on both sides. Issue 2 – May 2012 www.diodes.com © Diodes Incorporated 2011 1 of 8 AL8807EV4 Quick Start Guide Suitable Test Equipment Count Description 1 Adjustable Power Supply, 12V 2A 2 Digital Multimeter 1 Digital Storage Oscilloscope 2 LED, high brightness, “Dragon Diamond”, series connected on suitable heat conducting PCB Manufacturer Part Number Thurlby Thandar CPX400A Fluke 179 Tektronix TDS2024B Osram CAUTION: The LEDs are very bright. Ensure they are hidden from direct view, or covered with a dispersing filter. The lid from an aerosol can is convenient for this. Also the LEDs are very hot. Do not touch!! Lamp Operation 1. Set the power supply to 12.0V but do not switch on. Set the current limit to 2.0A. 2. Connect up the AL8807EV4 board to the equipment as in Figure 1 below. Set DMM1 and DMM2 to measure current up to 2A. Figure 1: Test Schematic using VDC Input A POWER SUPPLY + DMM 2 - A DMM 1 K P1 P2 A A 3. Cover the LEDs to avoid dazzling. 4. Switch on the power supply. This should illuminate the LEDs. Note that the input current (DMM1) is approximately 690mA. The output current (DMM2) is approximately 1.12A. The input voltage can be varied from approximately 9VDC to 30VDC and the current regulation observed is typically within ±2%. Issue 2 – May 2012 www.diodes.com © Diodes Incorporated 2012 2 of 8 AL8807EV4 Observe Switching Waveform 5. The switching waveform can be observed on an oscilloscope. 6. Set the oscilloscope as follows: Channel 1 sensitivity: Time base: Trigger Source: Trigger Mode: 2V/div (at probe tip) 1µs/div CH1 Auto 7. Connect the ground lead of a 10x probe to the supply negative terminal near P2 of the AL8807EV4, and touch the probe tip onto the anode of D1 as in Figure 2 below. On the oscilloscope, press RUN/STOP to capture the waveform. The cursor readout indicates a switching frequency of 440kHz approximately. Figure 2: A POWER SUPPLY + DMM 2 - A DMM 1 K P1 P2 A Figure 3: Oscilloscope Waveform Issue 2 – May 2012 www.diodes.com © Diodes Incorporated 2012 3 of 8 AL8807EV4 Schematic Issue 2 – May 2012 © Diodes Incorporated 2012 D1 DFLS240 SW R2 0R2 L2 TDK MPZ2012S300A VIN VINF Anode Anode 8 D5 SBR2A30 L1 AL8806 4 SW CTRL SW 5 6 Cathode Cathode 15uH GND GND 100nF 100nF 3 C6 1.5nF C3 2 C10 100nF C7 1.5nF D4 SBR2A30 470uF C9 TAB AC2 C2 4.7uF 50V X7R C4 1uF U1 AL8807 SET Vin C1 NC P2 C5 1.5nF AC1 9 4 of 8 P1 D2 SBR2U30P1 7 D3 SBR2U30P1 1 R1 0R15 C8 1.5nF AL8807EV4 www.diodes.com GND AL8807EV4 PCB Copper Layout & Silk Screen – Top PCB Copper Layout & Silk Screen –Bottom Issue 2 – May 2012 www.diodes.com © Diodes Incorporated 2012 5 of 8 AL8807EV4 Parts List Count Designator Description Package 1 C1 Capacitor, 470uF, 25V Aluminium Electrolytic Radial, 10 x 12.5mm Manufacturer Part Number Rubycon 25ZLH470M 1 C2 Capacitor, 4.7µF 10% 50V X7R 1210 Kemet C1210X475K5RAC 3 C3 C9 C10 Capacitor, 100nF 10% 50V X7R 0805 Kemet NIC NMC0805X7R104K50TRPF 1 C4 Capacitor, 100nF 10% 50V X7R 1206 Kemet NIC NMC1206X7R104K50TRPF 4 C5 - C8 Capacitor, 1.5nF 10% 50V or 100V, COG 0805 generic 1 L1 Inductor, shielded, 15µH 20% 6.6 x 6.6mm Coilcraft NIC Würth MSS7341-153ML NPIS64D150MTRF 744777115 1 L2 Inductor, ferrite bead, 6A, 30ohms @100MHz 0805 TDK MPZ2012S300A 1 R1 Resistor, 0.15ohms 1% 250ppm 125mW 0805 generic 1 R2 0805 generic 1 D1 4 D2 - D5 1 U1 Resistor, 0.2ohms 1% 250ppm 125mW Diode, schottky, 30V 2A DFLS230 (alternatives: DFLS230L or LH) Diode, Super Barrier Rectifier, 30V 2A SBR2U30 IC, LED Driver, AL8807 C1210X475K5RAC C1206104K5RAC7800 PowerDi123 Diodes Inc DFLS230-7 PowerDi123 Diodes Inc SBR2U30P1-7 MSOP-8EP Diodes Inc AL8807MP8-13 I/O Count Designator Description Function 1 Manufacturer P1 Solder pad VDC, VAC Input 1 P2 Solder pad VDC, VAC Input 1 A Solder pad LED Anode load 1 K Solder pad LED Cathode load Part Number Recommended Operating Conditions Symbol Parameter Min Max Units VDC Input Supply Voltage, VDC 8 30 V VAC Input Supply Voltage, VAC 8 20 Vrms VOUT Load voltage ( 1 to 3 LEDs) 0 10 V TA Operating Ambient Temperature -40 +105 °C Issue 2 – May 2012 www.diodes.com © Diodes Incorporated 2012 6 of 8 AL8807EV4 Current Setting The LED current is set by the sense resistor value, RSENSE. On this PCB, there are two resistors in parallel. RSENSE = R1 * R2 / (R1 + R2) For the schematic values this gives a resistance of 0.15 * 0.2 (0.15 + 0.2) = 0.0857 ohms. The LED current flows through RSENSE. The sense voltage is 100mV, so the LED current is simply ILED = 0.1/ RSENSE For the schematic values this gives an LED current of 0.1/0.0857 = 1.167 A nominally. In practice there is a slight reduction in current partly due to the resistance of the PCB copper, depending on the PCB layout. At 1.1A this reduction is typically about 5% using AL8807EV4. The following table gives commercially available resistor values for typical current requirements, allowing a current error of 3% maximum not including the effect of PCB copper. A power limit of 125mW is assumed for the 0805 size resistors with 50% de-rating. LED Current 150mA 300mA 380mA 500mA 660mA 1A 1.1A R1, ohms 0.68 0.33 0.51 0.2 0.15 0.2 0.15 R2, ohms DO NOT FIT DO NOT FIT DO NOT FIT DO NOT FIT DO NOT FIT 0.2 0.2 Performance The performance of the AL8807EV4 demonstrated shows the capability to regulate LED current. The LED current of 1.1A is approximately 5% lower than the calculated value. This is partly due to copper resistance. With a load of 2 LEDs, the current changes by less than ±2% over the input voltage range from 9VDC to 30VDC. With 2 LEDs and a supply of 12VDC, the switching frequency is approximately 440kHz. For further advice, please contact your local Diodes Field Applications Engineer, or one of our sales offices listed on the back page of this document. 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