DN06033/D Design Note – DN06033/D NCP3065 SEPIC LED Driver for MR16 Device Application Input Voltage Output Power Topology I/O Isolation NCP3065 NCV3065 Solid State, Automotive and Marine Lighting 8-20 V, 12Vdc, 12Vac <15 W SEPIC NONE Other Specifications Output Voltage Current Ripple Nominal Current Max Current Min Current Output 1 Output 2 Output 3 Output 4 7.2-23 V <15 % 0.35, 0.7, 1.0 A 1A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A Minimum Efficiency 75% Circuit Description This design note describes a DC-DC converter circuit that can be easily configured to drive LEDs at several different output currents and voltage. It can be configured for either AC or DC low voltage input. It is proposed for driving High Brightness LEDs such as Lumileds LuxeonTM, Osram OstarTM, TopLEDTM and Golden Dragon as well as the Cree XLAMPTM etc. and it is designed for replace traditional MR16 bulbs with LEDs like mentioned above. MR16 input voltage range is usually 12 Vdc and 12Vac but you can use this circuit for wide input voltage. You have to only think about right component selection. The circuit uses the NCP3065 switching regulator configured to drive a series string of LEDs in constant current mode. NCP3065 is monolithic power switching regulator capable of delivering 1.5A at output voltages 0.235V to 35V. Circuit benefit is in the wide input and output voltage range and in the high efficiency and small application volume. The brightness of the LED or light intensity as measured in Lumens is proportional to the forward current flowing through the LED. Dimming PWM input is included. Pulse Feedback resistor (R2) is used to vary the slope of the oscillator ramp, achieve duty cycle control and stabilize switching frequency in the wide input voltage range. October 2007, Rev. 0 This demo board can be ordered from ON web site, its name is NCP3065D1SLDGEVB. Key Features y Buck-Boost operation y Wide input and output operation voltage y Regulated average output current y Overcurrent and overvoltage protection included y PWM Dimming input y High operation frequency y Minimal input and output current ripple y Whole application in circle with 30mm diameter y Designed for MR16 bulbs www.onsemi.com Figure 1 – Demo board top view 1 DN06033/D Schematic Figure 2 – MR16 SEPIC converter schematic Design Notes A SEPIC (single-ended primary inductance converter) is distinguished by the fact that its input voltage range can overlap the output voltage range. There is principal schema is shown in Figure 3. Figure 3 – Principal SEPIC schematic When switch SW is ON, energy from the input is stored in inductor L1. Capacitor CP is connected in parallel to L2, and energy from CP is transferred to L2. The voltage across L2 is the same as the CP voltage, which is the same as the input voltage. At this time, the diode is reverse biased and COUT supplies output current. If the switch SW is OFF, current in L1 flows through CP and D1 then continues to the load and COUT. This current recharges CP for the next cycle. Current from L2 also flows through D1 to the load and COUT that is recharging for the next cycle. Inductors L1 and L2 could be uncoupled, but then they must be twice as large as if they are coupled. Another advantage is that if coupled inductors are used there is very small input current ripple. Values of coupled inductors are set by these equations D= + VF VOUT 7,2 + 0.4 min = = 0,487 + VIN + VF 7,2 + 8 + 0.4 VOUT min min Load current 350mA: ΔI = r ⋅ I OUT D 0.487 = 0.8 ⋅ 0.35 ⋅ = 0.266 A 1− D 1 − 0.487 October 2007, Rev. 0 ⋅D V 8 ⋅ 0.487 = L1, 2 = IN min = 29 .3μH 2 ⋅ f ⋅ ΔI 2 ⋅ 250 ⋅ 10 3 ⋅ 0.266 www.onsemi.com 2 DN06033/D Load current 700mA: ΔI = r ⋅ I OUT V ⋅D 8 ⋅ 0.487 L1,2 = IN min = = 14.6 μH 2 ⋅ f ⋅ ΔI 2 ⋅ 250 ⋅ 103 ⋅ 0.532 D 0.487 = 0.8 ⋅ 0.7 ⋅ = 0.532 A 1− D 1 − 0.487 Load current 1000mA: ΔI = r ⋅ I OUT ⋅D V 8 ⋅ 0.487 L1,2 = IN min = = 10.3μH 2 ⋅ f ⋅ ΔI 2 ⋅ 250 ⋅ 103 ⋅ 0.76 D 0.487 = 0.8 ⋅ 1 ⋅ = 0.76 A 1− D 1 − 0.487 where r is the maximum inductor current ripple factor. The nearest coupled inductor values for the 0.7 A variant is 15 μH. Output current is set by RS (R6, R7 and R8) value. So this resistor can be calculating by the formula: RS = 0,235 I OUT . On the evaluation board, the value of RS can be selected by jumpers J3, J4. When both are open output current is setup to 350mA. With J3 shorted, the output current increase to 700mA and when you shorted both J3 and J4 you setup output current to1A. To protect the circuit against high output voltage on light loads or load disconnection, output voltage is clamped by a Zener diode (D5) to approximately 24.5 V. External power MOSFET is forced by internal NPN Darlington transistor, by driver from external diode D2 and by PNP transistor Q2. Maximum MOSFET current can be calculated by this formula: U max ⎛ 0,8 ⎞ 23 ⎛ r⎞ I Q1 max = ⎜1 + ⎟ ⋅ I OUT OUT = ⎜1 + = 2,5 A ⎟ ⋅ 0,7 ⋅ U IN min 2 ⎠ 8 ⎝ 2⎠ ⎝ To minimize power MOSFET conductance losses, it is recommended to select a transistor with small RDSON. To minimize switching losses, it is recommended to select a transistor with small gate charge. Power MOSFET must also have a breakdown voltage higher than: VFETPK = VIN + VOUT = 20 + 23 = 43V Switch peak current protection is set by R1 at I PKset = 0,2 R1 A suitable value is higher than maximum switch current. R1 < 0,2 I Q1 max = 0,2 = 80mΩ 2,5 Diode D1 is stressed with reverse voltage VD1 max = VIN + VOUT = 20 + 23 = 43V and with current I D1 = I OUT = 0,7 A The C1 coupling capacitor is stressed on input voltage and on current VOUT max 23 D max = = = 0,74 VOUT max + VIN min 23 + 8 I C 2 RMS = VOUT ⋅ I OUT VIN 1 − D max 23 ⋅ 0,7 1 − 0,74 = = 1,2 A D max 8 0,74 and its minimal value is C2 > October 2007, Rev. 0 I OUT ⋅ D min 0,7 ⋅ 0,47 = = 2μF 0,05 ⋅ V IN min ⋅ f 0,05 ⋅ 8 ⋅ 250 ⋅10 3 www.onsemi.com 3 DN06033/D Application LEDs configuration Vf = 7.2V Vf = 10.8V Vf = 14.4V Output current 350mA 700mA 1000mA 350mA 700mA 1000mA 350mA 700mA 1000mA Pulse feedback resistor R2 value Input voltage 12 Vdc 12 Vac 7.5k 5.1k 6.2k 4.3k 5.1k 5.1k 8.2k 6.8k 8.2k 5.1k 9.1k 8.2k 13k 12k 10k 10k 28k 11k J2-3 input is used for dimming. The dimming signal level is 2-10 V or can be used TTL compatible signal. Recommended dimming frequency is about 200 Hz. For frequencies below 100 Hz the human eye will see the flicker. The low dimming frequencies are EMI convenient. Dimming function is based on the NCP3065’s feedback input. The second way to achieve this is to use the IPK pin as can be seen in application note AND8298. Conclusion This circuit was developed based on requirements for replacing traditional MR16 bulb with new High brightness LEDs. This circuit is ideal in applications with strings of two to six LED chips connected in series, everywhere where input and output voltage overlap. The advantages of this circuit include its small size, low price, wide input and output voltage ranges, and very small input current ripple. Figure 4 – Application example top side October 2007, Rev. 0 www.onsemi.com 4 DN06033/D PC Board Figure 5 – components position on PCB Figure 6 – PCB’s top side – not in scale Figure 7 – PCB’s bottom side – not in scale October 2007, Rev. 0 www.onsemi.com 5 DN06033/D Table 1– Bill of materials Designator Quantity Description Value Tolerance Footprint Manufacturer Manufacturer Part Number Substitu tion Allowed Lead Free C1 1 Ceramic capacitor SMD 47uF/25V 20% 1812 Taiyo Yuden TMK432C476MM-T Yes Yes C2, C3 2 Ceramic capacitor SMD 47uF/16V 20% 1210 Taiyo Yuden EMK325BJ476MM-T Yes Yes C4 1 Ceramic capacitor SMD 3.3nF 5% 0805 TDK C2012C0G1H332J Yes Yes C5 1 Ceramic capacitor SMD 10uF/25V 20% 1210 Taiyo Yuden TMK325BJ106MM-TR Yes Yes C6 1 Ceramic capacitor SMD 100nF 10% 0805 TDK C2012X7R1H104K Yes Yes C7 1 Ceramic capacitor SMD 100pF 5% 0805 TDK C2012C0G1H101J Yes Yes C8 1 Ceramic capacitor SMD 2.2nF 10% 0805 TDK C2012X7R2A222K Yes Yes MBRS260T3G - SMB ON Semiconductor MBRS260T3G No Yes BAT54T1G - SOD-123 ON Semiconductor BAT54T1G No Yes MMSZ24T1G 5% SOD-123 ON Semiconductor MMSZ24T1G No Yes Yes D1 1 Surface Mount Schottky Power Rectifier D2 1 Schottky Diode 30V D5 1 J1 1 Zener Diode 500 mW 24 V AMPMODU Mod II Right-Angle Horizontal PCB Connector J2 1 Input connector J3, J4 2 Jumper, RM 2.54 mm J3, J4 2 Q1 1 Jumper, RM 2.54 mm, PCB pin's Power MOSFET 32Amps, 60Volts, Logic Level, N-Channel Q2 1 PNP General Purpose Transistor Q3 1 General Purpose Transistor NPN 5535676-5 - - TYCO 5535676-5 Yes DG350-3.50-03 - - Degson DG350-3.50-03 Yes Yes Jumper - 2.54 Harwin M7686-05 Yes Yes Jumper - PCB pin's - 0003 Harwin M20-9990205 Yes Yes NTD32N06LT4G - DPAK ON Semiconductor NTD32N06LT4G No Yes MMBT3906LT1G - SOT-23 ON Semiconductor MMBT3906LT1G No Yes BC817-40LT1G - SOT-23 ON Semiconductor BC817-40LT1G No Yes R1 1 Resistor SMD WSL1206 -0.05R/0.5W 1% 1206 Welvyn WSL1206 -0.05R/0.5W Yes Yes R2 1 Resistor SMD 8k2 1% 0805 Vishay CRCW08058K20FKEA Yes Yes R3 1 Resistor SMD 1k5 1% 0805 Vishay CRCW08051K50FKEA Yes Yes R4 1 Resistor SMD 1k 1% 0805 Vishay CRCW08051K00FKEA Yes Yes R5 1 Resistor SMD 1k2 1% 0805 Vishay CRCW08051K20FKEA Yes Yes R6, R7, R8 3 Resistor SMD 0R68 5% 1206 Tyco Electronics RL73K2BR68JTD Yes Yes R9 1 Resistor SMD 10k 1% 0805 Vishay CRCW080510K0FKEA Yes Yes R10 1 Resistor SMD 100R 1% 0805 Vishay CRCW0805100RFKEA Yes Yes T1 1 Dual inductor PF0553.153NL - - Pulse Eng. PF0553.153NL Yes Yes IC1 1 Constant Current Switching Regulator NCV3065MNTXG - DFN ON Semiconductor NCV3065MNTXG No Yes October 2007, Rev. 0 www.onsemi.com 6 Comments DN06033/D Measurements Figure 8 – Line regulation for VIN = 12Vdc, IOUT = 350 mA Figure 9 – Line regulation for VIN = 12Vdc, IOUT = 700 mA October 2007, Rev. 0 www.onsemi.com 7 DN06033/D Figure 10 – Efficiency for VIN = 12Vdc, IOUT = 350mA and 700 mA Figure 11 – Line regulation for VIN = 12Vac, IOUT = 350 mA October 2007, Rev. 0 www.onsemi.com 8 DN06033/D Figure 12 – Line regulation for VIN = 12Vac, IOUT = 700 mA Figure 13 – Efficiency for VIN = 12Vac, IOUT = 350mA and 700 mA October 2007, Rev. 0 www.onsemi.com 9 DN06033/D Figure 14 – Dimming linearity, dimm.frequency 200Hz 1 © 2007 ON Semiconductor. Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its products at any time, without notice. Design note created by Petr Konvicny, e-mail: [email protected] October 2007, Rev. 0 www.onsemi.com 10