STM32L151CC PWM Ausgang funktioniert nicht

GPIO_InitTypeDef GPIO_InitStructure;

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

TIM_OCInitTypeDef TIM_OCInitStructure;

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB, ENABLE);

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, s)

// Ausgangs-Pin für das PWM-Signal

GPIO_InitStructure.GPIO_Pin            = GPIO_Pin_13;

GPIO_InitStructure.GPIO_Mode           = GPIO_Mode_AF;

GPIO_InitStructure.GPIO_Speed          = GPIO_Speed_40MHz;

GPIO_InitStructure.GPIO_OType          = GPIO_OType_PP;

GPIO_InitStructure.GPIO_PuPd           = GPIO_PuPd_NOPULL;

GPIO_Init(GPIOB, &GPIO_InitStructure);

// Mapping für den PWM Ausgangs-Pin

GPIO_PinAFConfig(GPIOB, GPIO_PinSource13, GPIO_AF_TIM4);

// Konfiguriert den Timer

TIM_TimeBaseStructure.TIM_Period         = 100 - 1;

TIM_TimeBaseStructure.TIM_Prescaler      = (SystemCoreClock / 1000000) - 1;

TIM_TimeBaseStructure.TIM_ClockDivision  = TIM_CKD_DIV1;

TIM_TimeBaseStructure.TIM_CounterMode    = TIM_CounterMode_Up;

TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);

// Konfiguriert den PWM Kanal

TIM_OCInitStructure.TIM_OCMode           = TIM_OCMode_PWM1;

TIM_OCInitStructure.TIM_OutputState      = TIM_OutputState_Enable;

TIM_OCInitStructure.TIM_Pulse            = 0;

TIM_OCInitStructure.TIM_OCPolarity       = TIM_OCPolarity_High;

TIM_OC1Init(TIM4, &TIM_OCInitStructure);

TIM_OC1PreloadConfig(TIM4, TIM_OCPreload_Enable);

TIM_ARRPreloadConfig(TIM4, ENABLE);

TIM_Cmd(TIM4, ENABLE);

// Später dann Änderung der Helligkeit mit

int brightness; // 0=0%, 1=10%, 10=100%

int pulse = 10 - brightness * 10;

TIM_OCInitStructure.TIM_OCMode           = TIM_OCMode_PWM1;

TIM_OCInitStructure.TIM_OutputState      = TIM_OutputState_Enable;

TIM_OCInitStructure.TIM_OCPolarity       = TIM_OCPolarity_High;

TIM_OCInitStructure.TIM_Pulse            = pulse;

TIM_OC1Init(TIM4, &TIM_OCInitStructure);