通过对PWM占空比的调节,实现小灯的渐亮的功能,当占空比为100％时 再从0％逐渐增加.PWM的周期一定要足够的快,否则其输出电压的波动范围很大,且测不出一个稳定的电压值,这样通过就观察不到小灯渐 效果. 另外,在改变PWM的周期和占空比之前和之后要分别禁止使用　TPM1,否则改变不起作用.(The PWM duty cycle regulation, realize the lights brightening function, when the duty ratio is 100% and then increased gradually from 0%.PWM cycles must be fast enough, otherwise the output voltage fluctuation range is large, and cannot measure a stable voltage value, this is not observed by lights gradually effect. In addition, in the period of change of PWM and duty ratio before and after respectively to prohibit the use of TPM1, otherwise the change does not work.)