AL8812EV1 User Guide General Description The MR16 LED Driver Module Evaluation board shows how to use the new AL8812 with integrated MOSFET in one package as a Boost LED driver for an inexpensive PFC front end and the new AL8807A as a Buck LED driver for a cost effective MR16 LED Driver circuit from which high PFC (~0.9) can be achieved. AL8812EV1 Specifications Key Features Evaluation Board Integrated 60V, 3.6A MOSFET Non-Dimmable or Triac Dimmable Front end Constant On time PFC circuit using the AL8812 Boost LED Driver New AL8807A Buck LED Driver PFC for the 12VAC input allowing multiple MR16 units on one transformer Compatible with Electronic Transformers Applications MR16 LED Bulb Desktop lamps Under the counter lamps Parameter Value Input Voltage LED Current Number of LEDs 12VAC 660mA (Adjustable) 3 LEDs in series (Under Tested) 1.06 ” x 0.71” XY Dimension LED- AC+ LED+ ACFigure 1: Top View AC+ LED+ LED- ACFigure 2: Bottom View Connection Instructions Input Voltage: 12VAC (AC+, AC-) LED Outputs: LED+ (Red), LED- (Black) AL8812EV1 Rev1 April 2014 www.diodes.com Page 1 of 18 AL8812EV1 User Guide Block Diagram: 12VAC Input AL8812EV1 PFC Boost LED Driver AL8812 with integrated MOSFET Bridge rectifier Buck LED Driver AL8807A LEDs Phase Detect Triac Dimming Figure 3: Block Diagram Evaluation Board Schematic Figure 4: Evaluation Board Schematic AL8812EV1 Rev1 April 2014 www.diodes.com Page 2 of 18 AL8812EV1 User Guide Evaluation Board Layout Figure 5: PCB Board Layout Top View Figure 6: PCB Board Layout Bottom View AL8812EV1 Rev1 April 2014 www.diodes.com Page 3 of 18 AL8812EV1 User Guide Quick Start Guide 1. By default, the evaluation board is preset at 660mA LED Current by R3. 2. Ensure that the AC source is switched OFF or disconnected. 3. Connect the 12VAC AC line wires of power supply to two test points of “12VAC” on the left side of the board. 4. Connect the anode wire of external LED string to LED+ output test point. 5. Connect the cathode wire of external LED string to LED- output test point. 6. Turn on the main switch. LED string should light up. Bill of Material # 1 2 3 4 5 6 7 8 9 10 11 12 13 Name IC1 IC2 Q1 D1-D4, D6,D8,D9 D5,D7 L1 L2 R1 R2 R3 R4 R5, R10 R6 R7, R8, R12 14 15 R9 16 R11 17 C1, C3 18 C2, C5, C6, C10, C11 19 C4, C7 20 C8, C9 AL8812EV1 Rev1 April 2014 www.diodes.com Quantity 1 1 1 Part number 7 2 1 1 1 1 SBR3U60P1 1 1 2 1 RHM.25UCT-ND 3 1 1 2 ERJ-2RKF4701X 5 2 2 AL8812 AL8807A MMBT3904T-7-F BAV70-7-F 7447714151 ASPI-104S-101M-T ERJ-2RKF10R0X ERJ-2RKF4700X ERJ-2RKF2201X ERJ-2RKF1001X ERJ-2RKF5902X ERJ-3GEY0R00V RL1220S-R15-F C0402C102J5GACTU C2012X5R1E106K125 AB C1005X7R1H104K050 BB UKA1H330MDD1TD Manufacturer Diodes Inc Diodes Inc Diodes Inc Description Boost IC Buck LED Driver Diodes Inc Diodes Inc Wurth Abracon Panasonic Panasonic Rohm Semiconductor Panasonic Panasonic Panasonic Super Barrier Rectifiers Panasonic Panasonic Susumu Kemet 4.7kΩ Resistor 1/10W 1% 0402 SMD TDK 10µF Cer Cap 25V 10% X5R 0805 TDK Nichicon 100nF Cer Cap 50V 10% X7R 0402 NPN transistor BAV70 Dual diodes 150µH, 1.2A Inductor for PFC stage 100µH, 1.35A Inductor for Buck Stage 10Ω Resistor 1/10W 1% 0402 SMD 470Ω Resistor 1/10W 1% 0402 SMD 0.25Ω Resistor 1/2W 1% 1210 SMD 2.2kΩ Resistor 1/10W 1% 0402 SMD 1kΩ Resistor 1/10W 1% 0402 SMD 59kΩ Resistor 1/10W 1% 0402 SMD 0Ω Resistor 1/10W 1% 0603 SMD 0.15Ω Resistor 1/3W 1% 0805 SMD 1000pF Cer Cap 50V 5% 0402 SMD 33µF Aluminum Cap 50V 20% Radial Page 4 of 18 AL8812EV1 User Guide Functional Performance (Three series LEDs @660mA) AL8812EV1 Module Board Performance (without dimmer and electronic transformer) Manuf Board Type VIN (VRMS) IIN (IRMS) PIN (W) PF VLED (V) ILED (mA) PLED (W) Diodes Inc AL8812EV1 Module Board 12 765.1 8.46 0.93 9.59 645.1 6.15 ILED Ripple (%) 8 Functional Waveforms For 120VAC dimmable MR16 design bench testing: The electronic transformer type is Hatch RS12-150 / 150W. The dimmer type is Lutron SELV-300P. Following is a block diagram of the bench circuit that indicates voltage and current designations where the scope plots are functionally captured on the bench set-up. The bench set-up is used in the evaluation of the AL8812EV1 module dimmable MR16 design. Figure 7: Bench Set-up Circuit AL8812EV1 Rev1 April 2014 www.diodes.com Page 5 of 18 Efficiency (%) 72.7 AL8812EV1 User Guide Waveform #1 (Maximum Dimming) => Channel 1: V1; Channel 2: I1 AL8812EV1 Board (Full Brightness) Dimmer Voltage (V1) Dimmer Current (I1) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #2 (Dimming Control ILED=660mA full brightness) => Channel 1: V1 AL8812EV1 Board (Full Brightness) ILED=660mA (Full Brightness) Dimmer Voltage (V1) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 6 of 18 AL8812EV1 User Guide Waveform #3 (Dimming Control ILED=400mA) => Channel 1: V1 AL8812EV1 Board (ILED=400mA) ILED=400mA Dimmer Voltage (V1) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #4 (Dimming Control ILED=200mA) => Channel 1: V1 AL8812EV1 Board (ILED=200mA) ILED=200mA Dimmer Voltage (V1) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 7 of 18 AL8812EV1 User Guide Waveform #5 (Dimming Control ILED=26mA Lowest Brightness) => Channel 1: V1 AL8812EV1 Board (ILED=26mA Lowest Brightness) ILED=26mA Dimmer Voltage (V1) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #6 (Maximum Dimming) => Channel 1: V2; Channel 2: I2 AL8812EV1 Board (Full Brightness) Electronic Transformer Voltage (V2) Electronic Transformer Current (I2) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 8 of 18 AL8812EV1 User Guide Waveform #7 (Zoom-in for Maximum Dimming) => Channel 1: V2; Channel 2: I2 AL8812EV1 Board (Full Brightness) Electronic Transformer Voltage (V2) Electronic Transformer Current (I2) 3.26msec Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #8 (Dimming Control full brightness) => Channel 2: I2 AL8812EV1 Board (ILED=660mA Full Brightness) Electronic Transformer Current (I2) in 5A/DIV ILED=660mA (Full Brightness) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 9 of 18 AL8812EV1 User Guide Waveform #9 (Dimming Control ILED=400mA) => Channel 2: I2 AL8812EV1 Board (ILED=400mA) Electronic Transformer Current (I2) in 5A/DIV ILED=400mA Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #10 (Dimming Control ILED=200mA) => Channel 2: I2 AL8812EV1 Board (ILED=200mA) Electronic Transformer Current (I2) in 5A/DIV ILED=200mA) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 10 of 18 AL8812EV1 User Guide Waveform #11 (Dimming Control ILED=26mA Lowest Brightness) => Channel 2: I2 AL8812EV1 Board (ILED=26mA Lowest Brightness) Electronic Transformer Current (I2) in 5A/DIV ILED=26mA ( Lowest Brightness) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA Waveform #8 (Maximum Dimming) => Channel 1: V2; Channel 2: I2; Channel 3: I3 AL8812EV1 Board (Full Brightness) Electronic Transformer Voltage (V2) Electronic Transformer Current (I2) LED Output Current (I3) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 11 of 18 AL8812EV1 User Guide Waveform #9 (Maximum Dimming) => Channel 3: I3; Channel 1: V3 AL8812EV1 Board (Full Brightness) LED Output Voltage (V3) LED Output Current (I3) Condition: IN=120VAC; OUT=3 LEDs in series / 660mA AL8812EV1 Rev1 April 2014 www.diodes.com Page 12 of 18 AL8812EV1 User Guide Functional Data Curves AL8812EV1 Rev1 April 2014 www.diodes.com Page 13 of 18 AL8812EV1 User Guide Transformer Compatibility List 1) 120VAC to 12VAC Electronic Transformers without dimmers in 3 LEDs in series: Electronic Transformers (120VAC to 12VAC) Index Brand Model 1 RSA RT60A (60W) 2 HATCH RS12-150 (150W) 3 HATCH RS12-60M-LED (60W) 4 HATCH VS12-75W (75W) 5 HATCH RS12-60M (60W) 6 HATCH RS12-80M (80W) 7 HATCH RS12-105 (105W) 8 HATCH RS12-15M-LED (15W) Performance Result (No flicker) √ √ √ √ √ √ √ √ 2) 120VAC to 12VAC Electronic Transformers with dimmers in 3 LEDs in series Electronic Transformers (120VAC to 12VAC) Index Brand Model 1 HATCH RS12-60M-LED (60W) 2 HATCH VS12-75W (75W) 3 HATCH RS12-60M (60W) 4 HATCH RS12-15M-LED (15W) Note: 120VAC Dimmer Type LUTRON SELV-300P / 300W LUTRON MAELV-600 / 600W √ √ √ √ √ √ √ √ √ = No Flicker AL8812EV1 Rev1 April 2014 www.diodes.com Page 14 of 18 AL8812EV1 User Guide Application Information Circuit Description This design consists of three sections: 1) The input PFC circuit converts the 12VAC input voltage to a DC voltage around 30V (AL8812). 2) The output Buck LED Driver drives the three LEDs in series at a fixed current (AL8807A). 3) Finally, the phase-detect circuit generates a voltage proportional to the phase of the incoming AC voltage (when triac dimming is used). PFC Circuit The AL8812 Boost converter is a simple “Constant ON time controller”. By keeping the same ON time throughout the AC cycle, the circuit will draw a current that will closely match the voltage and result in a constant input current. This eliminates the classic peak current problem with a bridge rectifier and a large input filter capacitor. The PFC circuit includes the input bridge rectifier, EMI filter (if needed) and the AL8812 Boost converter. The AC input voltage is rectified by the bridge circuit and filtered by C1, R1, C4, and C5. This first filter removes the high frequency that is generated by the Electronic Transformer in the range of 20-30 KHz. An additional diode rectifier circuit (D5, C2) is used to generate a voltage that is used to power the circuit that will turn on/off the external MOSFET of the Boost converter. This circuit is very important as the gate drive of the MOSFET has to be greater than 3-4 volts throughout the AC cycle. The external MOSFET is used to reduce the heat dissipation in the AL8812. The AL8812 has a current limit resistor R3 which sets the maximum current allowed through the inductor L1. The output voltage is set by the divider R6, R5 to an output of around 35 volts. The output voltage is filtered by the two capacitors C8 and C9. These two capacitors store energy that will be used when the input voltage is low during the AC cycle. Buck LED Driver The AL8807A is a step-down DC-DC converter designed to drive LEDs with a constant current. The current through the LED is controlled by R11. In the present Evaluation board, the current is set to around 660mA based on a resistor value of 0.15Ω. The current is set using the “CTRL” input pin which in this new version of the IC can vary from 0 to 2.5V, controlling the current from 0mA to the maximum current at 2.5V. This control input pin is used to lower the LED current as the TRIAC dims the LED. In this way, the energy stored in the two output capacitors AL8812EV1 Rev1 April 2014 www.diodes.com Page 15 of 18 AL8812EV1 User Guide of the PFC circuit will be able to provide current throughout the AC cycle. TRIAC Phase Detection Circuit The phase of the TRIAC is detected by using an additional rectifier circuit that generates a voltage in proportional to the phase of the TRIAC Driver. This is done by rectifying the input AC voltage and averaging the energy using a resistor to charge a capacitor. Two additional resistors in series, R12 and R8, slowly discharge this circuit so it will follow the input phase change. The two resistors, R12 and R8, are used to scale the voltage so the range is from 0 to 2.6V to the Buck LED driver control pin. A simple transistor emitter follower circuit is used to drive a 1K resistor in the emitter circuit. This low resistance is needed to drive the input control pin of the AL8807A LED driver because the pin outputs a small current of 50uA, which limits the lowest control voltage to around 50 mV. Setting the LED output current (AL8807A): The LED output current is set using resister R11 and the formula: ILED = VTH / R11 where VTH is equal to 0.1V For a current of 660mA, R11 is about 0.15Ω. Setting the PFC Variables (AL8812) The choice for the size of the boost converter inductor selected in this design is based on a compromise which it is able to support a peak current to around 1.5A since the average input voltage will be around 12-14V. The boost converter (AL8812) includes a current limit resistor R3 which will limit the current through the inductor and thus the power delivered to the output load. The formula for the resistor is: IPK(switch) = 0.25V / R3 For a current limit of 1A, R3 is 0.25Ω. In this evaluation design, this value was selected based on having three LEDs in series drawing about 660mA. It was found that two 33µF capacitors mounted in parallel would just fit into the cavity of the MR16 bulb. The important design goal is to have the PFC circuit, which is used to always draw current from the Electronic Transformer. AL8812EV1 Rev1 April 2014 www.diodes.com Page 16 of 18 AL8812EV1 User Guide Performance Description The evaluation board allows the testing of different combinations of circuit component values to match the final design specifications. The main design goal is to have a constant load on the Electronic Transformer so that it will be operating throughout the AC cycle. This is accomplished when the input power is about the same as the output power. Overall, there are three major components that are essential to the operation of the circuit. The first component to select is the resistor (R11) in the Buck LED driver (AL8807A) that sets the final current through the LED string. This will set the amount of power the system needs. The second component is the value of the (R3) which limits the current provided to the output filter capacitors. This should be adjusted so that the boost input circuit by AL8812 LED driver is always running and thus providing a load to the Electronic Transformer. This usually means that the output voltage of the PFC circuit will have a large ripple. This will be okay as long as the lowest voltage is higher than the maximum final LED string voltage. The third component is the output capacitors (C8 and C9) of the PFC circuit. These should not be too large that the PFC circuit stops working. If it happens, the resonant circuit of the Electronic Transformer will become erratic and cause the LEDs to flicker. 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