LED温度的上升会使LED使用寿命缩短，所以需要考虑到散热因素。本篇应用介绍了安森美半导体线型恒流LED驱动器CAT4101的热能反馈技
AND9053/D Resistance r3 is recommended to keep close to R2@Tt 0.9 ED current value. To help estimate bridge components and feedback 0.8 resistor simple XLs calculator is provided. Example 55 0.7 calculation for selected r6=R=10k. r3=1. 8k. Vcc= 0 Temperature 5V,VO= Vrset+ VID2=2V, NTC resistances from epcos 0.6 datasheet for B57421V2103H062 R2@Tm= 1553 Ohm 0.5 (74C)and R2(@TI=1732 Ohm(70C)is 0.4 R (1732-1553)·5 @T0 +1553≈18510hm 40 Tamb= 27.C 0.3 Pin 10 W Temperature 10k·5 0.2 10k·5 1.8k+155310k+185130.1089V 35 measured at 0.1 1.8k·10k·5-0.1089·1.8k·10k 30 0 R ≈68.5k9 10 0 40 (18k+10k)·0.1089 TIME(minutes) Figure 6. Achieved Results, Inactive Thermal Foldback, Pin~10 W, Vin=12 V, Ta= 24C, Regular R2 0 R6 DM +oV Operation 9 0.9 D current 0.8 0.7 0.6 山60 Temperature 0.5 R 04当 50 Tamb~40°C Pin c 10 W 0.3 45 系口0T measured at heatsink 0.1 35 10 15 TIME(minutes) Figure 5. MCPCB Assembly, ToP Layer View Figure 7. Achieved Results, Activated Thermal Fold back. Pin-10 W Vin =12V. Ta-400C Conclusion and Application Example In an ideal case, foldback functionality should not be Please note according to ntc datasheet there is resistance activated during proper operation, but in the case of variation, therefore to match required temperature, precise unexpected situations like increased ambient temperature NtC resistors or individual resistance measurement at Tt improper installation, etc, it will help to protect lighting and Tm are required solution and keep its lifetime high. When an over tem perature condition occurs, the thermal foldback circuitry reduces the regulated current through the LEDS, while continuing to operate it(dimming). In Figure 9, practical application of 10 W LEd accent lamp is shown. PCB Layout for driver based on MCPCB (Metal Core Printed Circuit Board) is shown in Figure 5. Here, LED driver supply around 800 ma to three serial connected 3 W leds Achieved results for different ambient temperatures are shown in Figure 6(inactive thermal foldback, regular fixture functionality) and Figure 7(activated thermal foldback increased ambient temperature). As can be seen, calculated and achieved results are consistent. This approach can be applied to multichannel design for instance for street lighting, flower stimulation lights and many others Figure 8. Realization on MCPCB, Bergquist Al =1 mm http://onsemi.co 3 AND9053/D Figure 9. Application Example, 10 W LED Lamp http://onsemi.co AND9053/D Table 1. cAt4101 BOARD LIST OF COMPOnENTS Name Manufacturer Description Package Part number Quantity AX Ceramic Capacitor Size 1206 M1/35V C2 AVX Tantalum Capacitor TANT-32-16 22u/10V AV Tantalum Capacit TANT-60-32 10u/35V C4.C5 AVX Ceramic Capacitor Size 0805 100n 2 c6 AVX Ceramic Capacitor Size 0805 10n C7 AⅩ Ceramic Capacitor Size 1206 n 111 CON1 AVⅩ SSL AVX connector ssL9159-4P Interface CoN2 NA PCB Terminal TB2P5 LED 1 D1 ON Semiconductor Schottky Diode 3 A/60V SMB MBRS240 1 D2 ON Semiconductor Schottky Power Rectifier 0.5 A,30V SOD-123 MMSD4148 RO Vishay 0 Ohm shunt Size 1206 Comment 2 Bourns MF-SM Series Bourns MF-SM Series MF-SM-2920 PTC11A PTC Resettable Fl IC1 ON Semiconductor Low IQ Low Dropout 5V/100 mA Linear SOT-223 NCV8664 Regulator(Automotive) IC2 ON Semiconductor 3 A, Adjustable Output Voltage, Step D2PAK5 CAT4101 Down Switching Regula IC3 ON Semiconductor Low Voltage, Rail-to-Rail Operational SOIC 8 Mc33201 Amplifier R1 Yageo SMD Resistor RC1206 1/4 W Size 1206 670 Ohm R2 EPCOS 10k NTC Resistor Size 0805 B57421V2103Ho62 111 R Yageo SMD Resistor RC1206 1/4 Size 1206 10k R4 Yageo SMD Resistor RC0805 1/4W Size 0805 2k2 1 R5 Yageo SMD Resistor RC1206 1/4 W Size 1206 68k R6 Yageo SMD Resistor RC0805 1/4 W Size 0805 10k R7 Y SMD Resistor RC0805 1/4 W Size 0805 18k *Build note: All components except of LEDs are placed on MCPCB(Metal Core Printed Circuit Board), as shown in Figure 5 and Figure 8. The MCPCB is thermally attached to heat sink with LEDS(Figure 9). Ideally ntc resistor should be located at LED MCPCB or close to it, but in this application this was not really required ON Semiconductor and ON) arc rogistorod trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC rosorves the right to make changos without furthor notice Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. Al operating parameters, including "Typicals" must be validated for each customer applicatian by customer's technical experts. SCILLC does not convey any license under its patent ngts nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant in o the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLc oroduct could create a situation where personal injury or death may occur. Should Buyer purchase or use SCiLLC products for any such unintended or unauthorized application, Buyer shall indemnify anc hold Scillc and its officers, employees, subsidiaries, affiliates and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. 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