二极管是电流驱动型器件，PC817 输入电流控制在 8 ~ 15mA ，输出电流＜30mA 吧。http://wenku.baidu.com/link?url=GIg78Ql4rgzAWKMqLu1s_L8aI2wUEX2CV23tcn9Jkkg7xS1wBHdAXvIaeRx5qGmvwe9SiZ7_fS5uoNQ4o-k3w6tLLyXbSC4X1E4kGQEWp1u
