PWM Function of Axial DC Cooling fan

1. PWM technical background PWM (Pulse Width Modulation).

The traditional temperature-controlled fan uses a temperature probe near the fan bearing to detect the temperature of the fan‘s air inlet, thereby adjusting the fan‘s speed. Although this kind of temperature control solves certain problems, it has rough accuracy, and the speed of temperature control can only achieve high-speed and low-speed bipolar transmission. PWM is the abbreviation of pulse width modulation circuit, which has been widely used in industrial control and single-chip microcomputers. Intel combined it with the CPU temperature detection of the motherboard, and applied it to the precise control of the speed of the radiator fan, and achieved good results.

2. The functional characteristics of the PWM intelligent temperature control fan.

First of all, the PWM fan adjusts the fan speed by obtaining temperature information directly from the CPU, and there is no temperature measuring device on the fan. Depending on the CPU temperature, the temperature-controlled fan will have different speed adjustments corresponding to it, and the speed of the fan can be changed to four levels, five levels, or even more, which is basically a feeling of infinitely variable speed. Due to the real-time adjustment of the pulse width signal, the change of the fan speed is very sensitive, and the change of the speed and the CPU temperature are almost synchronized. Second, the PWM fan can maintain a very low speed when the computer is in standby. In standby, the CPU temperature is below 40-50 degrees, and its speed is only about one thousand revolutions, which greatly reduces the operating noise. The designed maximum speed, more than two thousand revolutions, will only appear when the CPU temperature is close to the limit temperature, that is, 65-67 degrees. Compared with the traditional temperature-controlled fan, it has a larger speed control range and better solves the problems of noise and performance.

3. Simple principle of PWM intelligent temperature control fan

On the motherboard with PWM function, in addition to the original temperature measurement circuit, a PWM control chip is added. Its function is to send out PWM pulse signals with different duty cycles according to the CPU temperature measured by the temperature measurement circuit. This pulse is a square wave. In a cycle, the high-level period of the square wave signal accounts for the proportion of the entire cycle, which we call the duty cycle. The entire cycle is a high level signal, the duty cycle is 100%, otherwise the duty cycle is zero. The simplest PWM temperature control circuit has an additional control circuit on the circuit board of the fan. We simply understand it as a triode, one of which is connected to the square wave pulse of PWM. If a high level appears on this level, Then the other two poles of the triode are in the conducting state, and if it is low, the other two poles are in the off state. If the duty cycle of the transmitted square wave pulse signal is 50%, that is, the high-level signal occupies half of a cycle, then the transistor will be in conduction state for half of a cycle. Through the conduction time of this transistor in one cycle, we can easily control the fan speed. If the duty ratio of the square wave pulse signal of the PWM can achieve multiple levels, then the fan speed can also achieve multiple levels.

When the PWM temperature-controlled fan is turned on, the speed will increase to the highest, and after a few seconds, it will decrease to the low speed level of standby. This feature is also the most obvious feature of the PWM intelligent temperature control fan. It can be used to determine whether the fan and the motherboard really have the PWM function, or whether its function is faulty, and can even be used as a reference judgment standard for true and false box radiators. .

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