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Speed control cooling fan, PWM duty ratio understanding

popularity: one thousand four hundred and twenty-nine Time of publication: June 15, 2020 17:13:45

What is PWM duty ratio

PWM is the abbreviation of pulse width modulation circuit. It has been widely used in industrial control and single chip microcomputer. Intel combines it with CPU temperature detection of motherboard, and applies it to Cooling fan Good results have been achieved in the precise control of the rotating speed.

In addition to the original temperature measuring circuit, a PWM control chip is added to the main board with PWM function. Its function is to send out PWM pulse signals with different duty ratios according to the CPU temperature measured by the temperature measuring circuit. This pulse is a kind of square wave. In a period, the proportion of the high-level period of the square wave signal to the whole cycle is called Control ratio

Why control the fan speed:

1. Reduce noise

2. Reduce power consumption;

3. Prolong the life of cooling fan.

What is the function of PWM duty ratio

The same fan can adjust the rotating speed in different environment;

To meet the needs of customers for noise, energy consumption and heat dissipation.

The simplest PWM temperature control circuit has more control circuits on the circuit board of the fan. We simply understand it as a triode, in which the first stage is connected with the square wave pulse of PWM. If there is a high level on this stage, the other two poles of the triode are in the on state; if it is low frequency, the other two poles are in the off state. If the duty cycle of the square wave pulse signal is 50%, that is, the high-level signal takes half of the time in a cycle, then the triode will be on for half of the time in a cycle. Through this triode in a cycle of conduction time, we can easily achieve the control of fan speed. If the duty cycle of PWM square wave pulse signal can achieve multiple levels, then the fan speed can also achieve multiple levels.


Keywords: Speed control cooling fan, PWM duty ratio understanding