论文部分内容阅读
驱动串联的高亮度LED可保证均 匀的亮度,但是这种方法一般需 要电源电压大于跨接在LED串上的总正向电压。一个开关方式升压变换器能以小于LED正向偏压的输入有效地驱动LED串,但是这样的电路同样不具有调节流经LED的电流的能力。增加一些电阻和两个晶体管可使电路升压且同时调节电流(见电路图)。 用5V工作时,标准的升压变换器(IC1、L1、D1和所有的电容器)把电压加在LED串上,足以产生由电流读出电阻器R4值设置的LED电流。R4的上
Driving a series of high-brightness LEDs ensures uniform brightness, but this method typically requires that the supply voltage be greater than the total forward voltage across the LED string. A switching mode boost converter can effectively drive LED strings with less than LED forward bias input, but such circuits also do not have the ability to regulate the current through the LEDs. Adding some resistors and two transistors can boost the circuit and adjust the current at the same time (see circuit diagram). With a 5V operation, the standard step-up converter (IC1, L1, D1 and all capacitors) applies a voltage across the LED string sufficient to generate the LED current set by the R4 value of the current sense resistor. R4 on