BSP450,高速转换，用于电源开关。3脚是TTL电平输入，4脚是工作电压输入，当3脚作用时，4脚与1脚导通。-BSP450, high-speed conversion, for the power switch. 3 is a TTL level input pin, 4 pin is the input voltage, when the role of 3 feet, 4 feet and 1 foot turn.