本文不提供完整程序，僅點出要點

1：時鐘配置。因為PWM輸出屬于復用功能，所以時鐘使能必須使能RCC_APB2Periph_AFIO ；

2：IO口使能。因為PWM屬于復用功能，所以IO輸出設置要配置成GPIO_Mode_AF_PP;而不能配置成普通輸出IO的GPIO_Mode_OUT_PP模式；

3：PWM初始化代碼如下，本程序只用通道3輸出，所以pwm輸出只配置了通道3，TIM_OC3Init(TIM3, &TIM_OCInitStructure);需要多通道輸出PWM則需要配置多個PWM輸出通道，通過改變TIM_Pulse 的值可以改變pwm的占空比（可以通過直接操作寄存器TIM3->CCR3=2400來實現）。

/* Time Base configuration */
  TIM_TimeBaseStructure.TIM_Prescaler = 0;   //預分頻為0
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;//向上計數
  TIM_TimeBaseStructure.TIM_Period = 4800; //8191=8.789 KHz, 4095=17.57 KHz,頻率太高超過人耳聽力范圍
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;    //時鐘分頻系數為0
  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;   //計數周期數為0 
  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);   //TIM3配置參數寫入

     /* Channel 1, 2,3 and 4 Configuration in PWM mode */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;             //pwm模式選擇PWM2
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;  //正向通道輸出使能
 // TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;   //反向通道輸出使能
  TIM_OCInitStructure.TIM_Pulse = 2400;                 //占空比設置
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;     //正向通道輸出極性
  //TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCPolarity_Low;         //反向通道輸出極性
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;  //正向通道閑散電平
  //TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;   //反向通道閑散電平
  TIM_OC3Init(TIM3, &TIM_OCInitStructure);
  TIM_OC3PreloadConfig(TIM3,TIM_OCPreload_Disable);
  TIM_ClearITPendingBit(TIM3,TIM_IT_CC3);

  TIM_Cmd(TIM3, ENABLE);
  TIM_CtrlPWMOutputs(TIM3, ENABLE);