The traditional temperature-controlled fan utilizes a temperature probe near the fan bearing to detect the temperature of the air inlet of the fan so as to adjust the rotation speed of the fan. Although this kind of temperature control solves certain problems, it has a rough accuracy, and the temperature-controlled rotation speed can only achieve high-speed and low-speed bipolar transmission. PWM is the abbreviation of pulse width modulation circuit. It has been widely used in industrial control and microcontroller. Intel integrated it with the CPU temperature detection of the motherboard to apply it to precise control of the speed of the radiator fan, and achieved good results.
The simple principle of the PWM intelligent temperature control fan is on the motherboard with PWM function, in addition to the original temperature measurement circuit, an additional PWM control chip, his role is based on the temperature measured circuit temperature of the CPU, issued a different Duty cycle PWM pulse signal. This pulse is a kind of square wave. In one cycle, the high-level period of this square-wave signal accounts for the proportion of the entire cycle, which we call the duty cycle. The entire cycle is a high signal, the duty cycle is 100%, and the duty cycle is zero. The simplest PWM temperature control circuit has a control circuit on the fan's circuit board. We simply understand it as a triode, in which the first-order and PWM square-wave pulses are connected. If there is a high level at this stage, The other two poles of the triode are in a conducting state. If it is a low level, the other two poles are in a disconnected state. If the duty cycle of the square-wave pulse signal sent out is 50%, that is, the high-level signal occupies half the time of one cycle, then this transistor will be in a conducting state for half of the cycle. Through this transistor's turn-on time in one cycle, we can easily control the fan speed. If the duty cycle of the PWM square-wave pulse signal can be achieved in multiple levels, the fan speed can also be achieved in multiple levels.
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