如何用立琦RT8450正确地实现升降压LED,MR16解决方案
导读：本文描述了一个驱动解决方案，开发使用Richtek RT8450芯片组驱动三个高亮度led作为替代传统基与MR16的卤素灯泡。它能够从12 v交流电源为高亮LED提供350毫安恒流驱动。设计已经优化了部分计数和温度性能。在在透镜部分和更广泛的输入电压范围方面服务于5W LED。这种设计可以满足流明的要求。
主要特征:
输入电压：12V/24V直流或5~40V交流
降压升压拓扑结构，输入电压可低于或高于输出LED电压
输出电流：350mA
输出电流精度：±5%
高效：大于80%
亮度控制：直流电压或PWM
转换频率：1MHz
工作环境：-40℃ to 85℃
软启动功能
The device encompasses a full bridge and a freewheeling diode realized using extremely low leakage 1A, 20V schottky diodes to allow a nominal 12VAC input operations. The reference design has solder tags pins to bypass the bridge rectifier should the final lamp design to be used for purely DC operation.
The RT8450 is a new space saving and thermal efficient device specifically designed for thermal and space critical requirements of MR16 application, As the input voltage of MR16 is 12 VAC, a bridge rectifier is required to rectify the AC input to DC level in order to provide supply to RT8450 LED driver. With wide input operating voltage range of the RT8450 (from 4.5 VDC to 40 VDC), a small input capacitor can maintain continuous operation. The switching frequency is internally set to 1MHz, allowing the use of extremely small surface mount inductors and chip capacitors.To avoid the flick happened when the lower rectified voltage from AC input, the buck-boost topology is designed for MR16 application. The input voltage can be either higher or lower than LED output voltage. The LED current can be maintained its setting and kept the brightness in application by current senses control topology. The smaller sense resistance can be set the accurate output current easily. The circuit diagram of the MR16 lamp solution with RT8450 is shown in Figure 1, and Table 1 provides the listed component values and specific part numbers.
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