What is the cause of the speed regulation cooling fan startup latency
phenomenon: installed on the device speed regulation cooling fan, fan delay for a few seconds after the power supply turns, rotational speed control function is normal, after the cooling fan PWM control line disconnected, electric cooling fan rotation.
analysis: the cooling fan can speed the PWM control function is normal, but the fan does not turn there are two possible:
1, the PWM is low level.
2, duty ratio is too small, the fan can't start
detection: two oscilloscope probe, fan of the red and blue line, respectively, were to meet fans black line, power to the fan start within a few seconds, the PWM and whether to maintain a few seconds between low level, or the duty ratio is not small,
advice: fan PWM control hardware circuit design, the MCU PWM is not involved, give to the fans of PWM is a high level, the benefits is abnormal, PWM control of the fan is running, does not affect the cooling equipment.
the figure below: PWM is not involved, R201 is not short circuit;