DN05055/D Compact 90-135Vac Hi‐PF Boost LED Driver http://onsemi.com DESIGN NOTE Table 1. DEVICE DETAILS Device Application Input Voltage Output Power Topology I/O Isolation NCP1075 + NCP4328A LED Driver 90 – 135 Vac Up to 9 W Boost Non-isolated Table 2. OTHER SPECIFICATIONS Constant Current Output 30 mA Nominal Voltage 220 Vdc Maximum Voltage 250 Vdc Minimum Voltage 200 Vdc Typical Power Factor 0.98 Typical THDi 11% Typical Efficiency 90% Startup Time < 20 msec Circuit Description LEDs are off for a portion of every line cycle when the input voltage is below the LED forward voltage, more LEDs are needed to produce the desired lumen output. In addition, the LED lamp exhibits over 100% ripple at 100/120 Hz. The impact of low frequency ripple on human performance is not a new concern in the lighting world and there is work underway to study this effect and set acceptable guidelines for the amount of flicker in LED light sources which are more sensitive since there is no optical persistence as is found in filament lamps. Further information can be found at website: (http://www.lrc.rpi.edu/programs/solidstate/assist/flicker.asp) If the LED string can be configured such that the forward voltage VF is greater than the peak AC voltage, this opens the door to use a boost topology to drive the LEDs. The output voltage must be higher than the peak of the applied ac input. This implies 135 Vac × √2 = 191 Vdc as the minimum LED voltage suitable for this boost converter application. A boost converter can provide high power factor and low THD, regulate accurate current regardless of LED forward voltage and line variation, and address the ripple issue eliminating the need to design with higher quantities of LEDs (or LED area) to achieve the desired lumen output. Note that many low power LEDs can also be arranged to achieve the required high voltage which is particularly High voltage LEDs are becoming more popular and are now available from multiple LED manufacturers such as CREE and Philips-Lumileds, see Figure 1. These package LEDs may have typical forward voltages ranging from 24 to > 200 V. Philips Luxeon H CREE XT-E Figure 1. Example High Voltage LED Products The development of these types of LEDs has been driven in part by the desire to improve the power conversion from the AC mains voltage to the LED string voltage as well as simplifying the driver electronics. In fact in some cases they have been promoted as being “driverless” since a diode bridge and linear regulator can implement a very simple circuit. There are several drawbacks to this approach. As the © Semiconductor Components Industries, LLC, 2014 February, 2014 − Rev. 1 1 Publication Order Number: DN05055/D DN05055/D Open load protection is provided by the second half of the NCP4328A controller. Precise regulation allows an LED operating voltage close to the maximum rating of the boost filter capacitor without typical tolerance concerns for less accurate protection methods. Maximum output power for this specific NCP1075 design is limited by the peak current limit, switching frequency, and maximum on-time of the switcher to about 9 W. The inductor determines the peak current as a function of applied voltage and on-time. In this case, 2.2 mH satisfies the switcher limitations. The selected inductor should support a peak current of 400 mA without saturating. Due to the low current, winding resistance is not a significant factor, but should be considered for maximum operating temperature. The close proximity of components on the small PCB means magnetic coupling is possible with the EMI filter magnetics which could introduce unwanted noise in the ac input. These magnetic components should be spaced as far as possible to avoid possible coupling. A magnetically shielded boost inductor like the part shown in the BOM may improve EMI performance. Q1 modulates the FB control pin of the NCP1075 providing high power factor control. Q1 performs as a voltage follower based on the shape of the rectified ac input pulling the FB pin low at the ac zero crossings. Maximum current for the NCP1075 occurs when the FB pin is about 3.2 V. The resistor divider formed by R4 and R5 sets the voltage at the base of Q1, and the emitter tied to FB pin is one diode drop higher. R4 is selected to provide a balance between low impedance to drive Q1 and minimal dissipation. 280k meets these criteria by dissipating less than 100 mW. Note that a 1206 package is required due to voltage and power stress on this resistor. R5 is selected as 3.9 kW to satisfy the 3.2 V level with 135 Vac applied to the converter input. This nominal 6.5 watt solution will support a range of LED voltages provided the current is adjusted to maintain the target power level. A nominal LED string voltage of 218 volts is used; therefore the output current is 30 mA nominal. Selecting the current sense resistor, R7, is as simple as dividing the reference voltage by the output current: R7= Vref / Iout = 0.0625 / 0.030 = 2.08 W, or use 2 W attractive to distributed light applications such as linear tube replacements. As with many high performance LED drivers, the proposed boost converter provides a constant output current compensating for input line voltage range and variation in LED voltage including temperature variation. Shown below are the design guidelines for this driver: • Input Range: 90–135 Vac • Output Current: 30 mA Typical • Output Voltage: 220 Vdc Typical • Efficiency: > 88% • Power Factor: > 0.95 • Open Load Protection This design is based on the ON Semiconductor NCP1075 switching regulator which integrates a 700 V MOSFET with control functions in a space saving SOT-223 or PDIP-7 package. In addition to the many protection features, this monolithic solution provides an internal Dynamic Self-Supply eliminating the need for external bias components. Since no bias winding is required, an off-the-shelf low cost magnetic can be used for the boost inductor. Typically, a current mode control converter must utilize an analog multiplier to achieve high power factor. In this design example, a simple transistor follower is employed to force the converter to reduce current draw around the zero crossings of the ac line. Combined with a small capacitor after the input diode bridge, this control method provides high power factor by programming the line current to follow the applied ac line voltage wave shape. LED current regulation is controlled by modulating the on-time away from the zero crossings of the input sine wave. Since most of the power transfer in a high power factor converter occurs near the peaks of the sine wave, balancing the characteristic near the zero crossing with controlled switching near the peaks provides high power factor and tight LED current regulation. Constant current control is implemented with a sense resistor in series with the LED load. The voltage across this resistor is processed by a combined Constant Voltage/ Constant Current controller, the ON Semiconductor NCP4328A. An internal reference provides a nominal 62.5 mV level to the current control loop, and 1.250 V to the voltage control loop. These amplifiers are combined internally to provide a single output control pin in a compact 5 pin TSOP package. The significance of this dual controller is the very low nominal supply current of 105 mA. At this low level, the Dynamic Self-Supply of the NCP1075 is able to provide bias power to the controller as well. The bias network is as simple as a filter capacitor and a trace connecting the two devices. A 10 mF 315 volt output filter capacitor was selected to maintain small component size and good filtering. Derating maximum voltage stress to 80% prolongs the useful life of the capacitor, netting 252 volts maximum. Selecting a capacitor rated 105°C with long operating life also enhances reliability. http://onsemi.com 2 DN05055/D A resistor divider is used to monitor the output voltage, and in order to minimize dissipation, the upper resistor, R9, is selected at 2 MW. Given the voltage control loop has a reference of 1.250 volts, this means the lower divider resistor, R10, follows the equation: R10 = (Vref × R9) / (Vout – Vref) = (1.250 × 2 MW) / (252 – 1.250) = 9.97 kW, or use 10 kW A capacitor is required after the diode bridge, providing a low impedance at high frequency for the inductor charging current. Ideally, this capacitor will have minimal change in voltage as the inductor charges minimizing ripple which the EMI filter must attenuate. However, this capacitor must follow the rectified ac line voltage in order to provide high power factor. At this power level, 100 nF is a good balance between these factors. The design is complimented with an input filter comprised of two off-the-shelf compact drum inductors, an X-capacitor, transient voltage suppressor and a fuse. The X-capacitor and inductors should provide attenuation without excessive dissipation or reactive current which would degrade power factor. Two 1.5 mH inductors and a 47 nF capacitor were tested and found to meet emission requirements. A miniature axial fuse keeps the design compact and the 1 A rating helps in passing the surge current to the MOV transient suppressor without opening. The schematic is shown in Figure 3. A prototype unit was built targeting a small board outline designed to be compatible with popular lamp base enclosures. The narrow portion holding the EMI filter easily fits inside the E27 screw base to utilize all available volume. The wider portion accommodates the high voltage output capacitor and boost inductor. Figure 2 shows a photo of the PCB which measures 0.95 inches by 1.365 inches (24 mm by 35 mm). Figure 2. Demonstration Board Performance is highlighted in Figures 4 and 5 showing current regulation, efficiency, Power Factor, and THD. The conducted EMI profile meets the CISPR22 Class B limits. The signature is shown in Figure 6 and a Bill of Materials is shown in Table 3. This example supports a 90−135 Vac input range but this design can be further optimized for the 100 Vac mains voltage found in Japan if need be and will meet the harmonic content requirements of JIS61000-3-2 Class C. http://onsemi.com 3 N−1 F1 1 2 2 1 MOV_5MM RV1 R3 1 MW 6.2 kW R1 6.2 kW 744746 L2 1.5 mH 1 1 C1 47 nF R2 2 2 2 1 + − NCP1075 DRAIN 4 GND FB VCC U1 HD06T − − D1 C3 1 mF 3 2 1 L3 2.2 mH C4 1 nF 744747 R5 3.9 kW C2 100 nF 2 1 2 2 1 2 1 B D3 BAS16 C E Q1 BC857 R6 1 MW MUR130 D2 R4 280 kW C5 10 mF 1 2 3 C7 33 nF NCP4328 5 VCC VSNS GND 4 FBC ISNS U2 C6 1 nF 2 1 2 L−1 2 1 4 1 http://onsemi.com 1 Figure 3. Schematic R10 10 kW R9 2 MW 1 R7 2W 2 2 1 L1 1.5 mH R8 22 kW 34−1 33−1 DN05055/D 35 95% 34 94% 33 93% 32 92% 31 91% 30 90% 29 89% 28 88% 27 LED Current 87% 26 Efficiency 86% 85% 25 90 95 100 105 110 115 120 125 130 Input Voltage (Vac) 1 25 0.98 20 0.96 15 0.94 10 0.92 5 THDi Power Factor Figure 4. Current Regulation and Efficiency Power Factor THDi 0.9 0 90 95 100 105 110 115 120 Input Voltage (Vac) Figure 5. Power Factor and THD http://onsemi.com 5 125 130 Efficiency LED Current (mA) DN05055/D DN05055/D NCP1075 LED Boost 120Vac 6 W dBuV 80 70 60 EN 55022; Class B Conducted, Quasi−Peak 50 EN 55022; Class B Conducted, Average 40 30 20 Average 10 0 −10 −20 1 10 10/16/2013 8:15:19 AM (Start = 0.15, Stop = 30.00) MHz Figure 6. EMI Signature http://onsemi.com 6 DN05055/D Table 3. BILL OF MATERIALS Ref Qty Type Value Description Tolerance Footprint Manufacturer Part Number C1 1 Capacitor 47 nF 310 Vac Metallized Polyester ±5% Box Vishay BFC233820473 C2 1 Capacitor 100 nF 250 Vdc Metallized Polyester ±10% Box Epcos B32520C3104K C3 1 Capacitor 1 mF 16 V Ceramic X7R ±10% 0603 SMD TKD C1608X7R1C105K080AC C4, C6 2 Capacitor 1 nF 50 V Ceramic NPO ±10% 0603 SMD TKD C1608C0G1H102K080AA C5 1 Capacitor 10 mF 315 V Electrolytic, 5000Hrs ±10% Radial Nichicon UPW2F100MPD C7 1 Capacitor 33 nF 50 V Ceramic X7R ±10% 0603 SMD TKD C1608X7R1H333K080AA D1 1 Diode HD06-T Rectifier bridge, 600 V, 0.8 A − SMD Diodes Inc. HD06-T D2 1 Diode MUR130 300 V, 1 A − SMA ON Semiconductor MUR130RLG D3 1 Diode BAS16 100 V, 200 mA − SOD−523 ON Semiconductor BAS16XV2T1G F1 1 Fuse 1A PICO, FAST, 125 Vac − Axial Littelfuse 0251001.MXL L1, L2 2 Inductor 1.5 mH Drum Inductor, 0.19 A ±10% Radial Wurth 7447462152 L3 1 Inductor 2.2 mH Drum Inductor, 0.32 A 10% Radial Wurth 7447471222 Q1 1 Transistor PNP 65 V, 100 mA − SOT−23 ON Semiconductor BC857BLT1G R1, R2 2 Resistor 6.2 kW 1/4 W 5% 1206 SMD Panasonic ERJ-8GEYJ622V R3 1 Resistor 1 MW 1/4 W 5% 1206 SMD Panasonic ERJ-8GEYJ105V R4 1 Resistor 280 kW 1/4 W 1% 1206 SMD Panasonic ERJ-8ENF2803V R5 1 Resistor 3.9 kW 1/10 W 1% 0603 SMD Panasonic ERJ-3EKF3901V R6 1 Resistor 1 MW 1/10 W 1% 0603 SMD Panasonic ERJ-3EKF1004V R7 1 Resistor 2W 1/4 W 1% 1206 SMD Vishay CRCW12062R00FKEA R8 1 Resistor 22 kW 1/10 W 1% 0603 SMD Panasonic ERJ-3EKF2202V R9 1 Resistor 2 MW 1/4 W 1% 1206 SMD Panasonic ERJ-8ENF2004V R10 1 Resistor 10 kW 1/10 W 1% 0603 SMD Panasonic ERJ-3EKF1002V RV1 1 MOV 264 V 150 Vac, 7.0J Varistor − Disc Littelfuse V240ZA05P U1 1 Controller NCP1075 Switcher, 65 kHz − SOT−223 ON Semiconductor NCP1075STAT3G U2 1 Controller NCP4328 Sec Side CV/CC Controller − TSOP6 ON Semiconductor NCP4328ASNT1G ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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