"220V Cooling Fan" 220V mains voltage through the transformer will become after the AC voltage of 15V, after rectifier circuit into a DC voltage of about plus or minus 15V. -15V Voltage to the buffer amplifier integrated amplifier to provide a negative voltage. "220V Cooling Fan" + 15V DC voltage by five after V into a stable 5V voltage regulator microcontroller and D / A digital-analog converter IC provides operating voltage, when the power is turned on 89C51 is reset voltage reset, the internal start execution of the program, and the corresponding output voltage. "220V Cooling Fan" switch button, press a button next machine in standby mode. Power no voltage output, press any key to boot.