占空比调节请教

2万 · 2018-8-17 09:23

STM32 PWM

static void TIM3_Mode_Config(void)
{
      TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
      TIM_OCInitTypeDef  TIM_OCInitStructure;

      u16 CCR1_Val = 200;

  TIM_TimeBaseStructure.TIM_Period = 999;

  TIM_TimeBaseStructure.TIM_Prescaler = 0;
  TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1 ;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR1_Val;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

  TIM_OC1Init(TIM3, &TIM_OCInitStructure);
  TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);

  TIM_ARRPreloadConfig(TIM3, ENABLE);

  TIM_Cmd(TIM3, ENABLE);
}

占空比是20%的时候，高电平占20%，亮度反而更亮，我想让80%占空比的时候亮，20%的时候弱，怎么实现呢