STM32RCT6标准库初始化定时器3PWM通道一，频率72kHz,占空比50%的代码

以下是使用STM32标准库初始化定时器3的PWM通道1，频率为72kHz，占空比为50%的代码：

#include "stm32f4xx.h"

void TIM3_PWM_Init()
{
  GPIO_InitTypeDef GPIO_InitStruct;
  TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
  TIM_OCInitTypeDef TIM_OCInitStruct;

  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

  GPIO_InitStruct.GPIO_Pin = GPIO_Pin_6;
  GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStruct.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
  GPIO_Init(GPIOA, &GPIO_InitStruct);

  GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_TIM3);

  TIM_TimeBaseInitStruct.TIM_Prescaler = 0;
  TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
  TIM_TimeBaseInitStruct.TIM_Period = 999;
  TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
  TIM_TimeBaseInitStruct.TIM_RepetitionCounter = 0;
  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitStruct);

  TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
  TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStruct.TIM_OutputNState = TIM_OutputNState_Disable;
  TIM_OCInitStruct.TIM_Pulse = 499;
  TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
  TIM_OCInitStruct.TIM_OCNPolarity = TIM_OCNPolarity_High;
  TIM_OCInitStruct.TIM_OCIdleState = TIM_OCIdleState_Reset;
  TIM_OCInitStruct.TIM_OCNIdleState = TIM_OCNIdleState_Reset;
  TIM_OC1Init(TIM3, &TIM_OCInitStruct);

  TIM_Cmd(TIM3, ENABLE);
}

其中，我们使用了GPIOA的第6个引脚作为PWM输出引脚，并将该引脚设置为复用模式(AF)。接着，我们初始化了定时器3的时钟，并配置了定时器的基本参数，比如分频系数、计数模式、周期等。最后，我们使用了TIM_OCInitStruct结构体初始化了PWM输出通道1，设置了PWM的占空比为50%。

请注意，以上代码仅供参考，具体实现还需要根据实际情况进行修改。