Principle of PWM intelligent controlled radiator fan
The technology background of PWM.
PWM is very strict in evaluating the cooling fan.
The traditional temperature control fan uses the temperature probe near the fan bearing to detect the inlet temperature of the fan, so as to adjust the speed of the fan. Although this temperature control has solved certain problems, but there is a rough precision, and temperature control speed can only be high-speed low-speed bipolar speed change. PWM is the abbreviation of pulse width modulation circuit. It has been widely used in industrial control and single chip microcomputer. In combines it with the CPU temperature detection of the motherboard, and applies it to the accurate speed control of the radiator fan, and achieves good results.
Functional characteristics of 2.PWM intelligent temperature control fan
Firstly, the PWM fan adjusts the fan speed directly from the CPU to obtain temperature information, there is no temperature measurement device on the fan.
According to different CPU temperatures, temperature-controlled fans will have different speed adjustments corresponding to it, and fan speed changes can be achieved four or five stages, or even more, basically the feeling of infinite speed change. Because of the real-time adjustment of pulse width signal, the change of fan speed is very sensitive, and the change of speed and CPU temperature is almost synchronous.
Second, the PWM fan can remain at a very low speed when the computer is on standby. In standby, the CPU temperature is below 450 degrees, its speed is only about 1000 revolutions, greatly reducing the noise of operation. The maximum speed of the design, more than 2,000 revolutions, will only occur 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 solve the problem of noise and performance.
Thirdly, the PWM temperature-controlled fan at the start of the moment, the speed will be raised to the highest, lasting several seconds, reduced to the standby low-speed level. This feature is also the most obvious feature of PWM intelligent temperature control fan, can be used to judge whether the fan and the motherboard really have PWM function, or whether its function is faulty, and even can be used as a reference to judge the true and false box radiator.
3.The simple principle of PWM intelligent temperature control fan on the main board with PWM function, in addition to the original temperature measurement circuit, a PWM control chip, his role is based on the temperature of the CPU measured by the temperature measurement circuit, the PWM pulse signal with different duty cycle. This pulse is a square wave, in a cycle, the high-level part of the signal of this wave accounted for the proportion of the whole cycle, we call it duty cycle. The whole cycle is a high level signal, and the duty cycle is 100%, otherwise the duty cycle is zero. The simplest PWM temperature control circuit, in the fan circuit board more than a control circuit, we simply understand it as a triode, which is connected to a PWM square wave pulse, if there is a high level on this stage, the other two poles of the triode in the on-state, if it is low level, the other two poles in the off-state. State. If the duty cycle of the square-wave pulse signal is 50%, that is, the high-level signal is half the time of a cycle, the transistor will be on for half the time of a cycle. Through the conduction time of the transistor in a cycle, it is easy to control the fan speed.
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