功率晶體使用問題，麻煩幫忙修正

http://www.circuitstoday.com/pwm-motor-speed-controller
功率晶體去做機殼風扇的轉速調整
PWM motor speed controller

Description. 文件說明
This circuit is designed as per a request made by Mr Vinoth from India. His requirement was a 12V/5A DC fan motor controller. I think this circuit is sufficient for this purpose. Quad 2 input Schmitt trigger IC CD4093 is the heart of this circuit. Out of the four Schmitt triggers inside the 4093, U1a is wired as an oscillator with adjustable duty cycle. The U1b, U1c, U1d buffers the output of the oscillator to drive the switching MOSFET Q1.The MOSFET drives the DC motor according to the switching pulse obtained from the oscillator. When R1 is varied the duty cycle varies and so do the speed of the motor. Diode D3 acts as a freewheeling diode.

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改P通道MOSFET，改後正負會相反，(-)線接到主機板就不會影響可變電阻的調整。
主機板cpu風扇輸出插座有3腳和4腳，3腳主機板會隨cpu溫度利用PWM控制轉速，4腳會隨cpu溫度變頻控制風扇轉速。
有些主機板有附程式可以設定cpu溫度到達幾度風扇該開始低速轉，線性隨溫度調高轉速，溫度上升到幾度風扇全速運轉