導讀：本文描述了一個驅動解決方案，開發使用Richtek RT8450芯片組驅動三個高亮度led作為替代傳統基與MR16的鹵素燈泡。它能夠從12 v交流電源為高亮LED提供350毫安恒流驅動。設計已經優化了部分計數和溫度性能。在在透鏡部分和更廣泛的輸入電壓范圍方面服務于5W LED。這種設計可以滿足流明的要求。
主要特征:
輸入電壓：12V/24V直流或5~40V交流
降壓升壓拓撲結構，輸入電壓可低于或高于輸出LED電壓
輸出電流：350mA
輸出電流精度：±5%
高效：大于80%
亮度控制：直流電壓或PWM
轉換頻率：1MHz
工作環境：-40℃ to 85℃
軟啟動功能
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.
