presented by:
Wayne_Chen

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DC Fan Speed Control PWM Signal Introduction
1. Speed Control Fan Structure
1-1. Use ON/OFF contr
Advantage：
Easy design and control method
Price cheaper
Disadvantage :
I. Power Dissipation is a design issue.
II. Not use friendly.
2. What is PWM Signal ?
PWM(Pulse Width Modulation): It’s a fixed frequency and pulse modulated for fan speed control.
Whenever change the duty cycle, the fan speed will be changed by system requirement
 The Purpose are :
1. The power dissipation will be saving.
2. And the working time will be increasing if the battery could not be charged outside. (especially NB system)
3. PWM control Methods introduction
3-1Speed Control Fan Structure (old version
 Use ON/OFF control by Transistor
Advantage：
I. Easy design and control method
II. Price cheaper.
Disadvantage：
I. Poor Reliability ( Transistor are On/OFF continuously)
II. Error judgment of tachometer signal.