diff --git a/app/by_fan_control.c b/app/by_fan_control.c
index d9c9bd6..64a5c60 100644
--- a/app/by_fan_control.c
+++ b/app/by_fan_control.c
@@ -70,8 +70,8 @@ void by_pwm_update_duty(uint32_t update_pwm_duty1, uint32_t update_pwm_duty2)
  */
 void by_pwm_power_duty(int32_t bpwm_duty_ls, int32_t bpwm_duty_rs, int32_t bpwm_duty_lb, int32_t bpwm_duty_rb)
 {
-    bpwm_duty_ls = clip_s32(bpwm_duty_ls, 500, 1000);
-    bpwm_duty_rs = clip_s32(bpwm_duty_rs, 500, 1000);
+    bpwm_duty_ls = clip_s32(bpwm_duty_ls, 500, 999);
+    bpwm_duty_rs = clip_s32(bpwm_duty_rs, 500, 999);
     bpwm_duty_lb = clip_s32(bpwm_duty_lb, 2500, 6000);
     bpwm_duty_rb = clip_s32(bpwm_duty_rb, 2500, 6000);
     pwm_set_duty(FAN_LS_PWM_PIN, bpwm_duty_ls);