说明：  1.如果输入一个高电平，而输出需要一个低电平时，首选择npn。 2.如果输入一个低电平，而输出需要一个低电平时，首选择pnp。 3.如果输入一个低电平，而输出需要一个高电平时，首选择npn。 4.如果输入一个高电平，而输出需要一个高电平时，首选择pnp
(1. if you enter a high level, while the output requires a low level, NPN is the first choice. 2. if the input and output of a low level, need a low level, PNP is the first choice. 3. if the input and output of a low level, requires a high level, NPN is the first choice. 4. if you enter a high level, while the output requires a high level, PNP is the first choice)