Patent ID: 7218073
Filing Date: 2007-05-15
Classification: F04D,Y02B

Abstract:
1. A fan motor speed control circuit, comprising: a digital/analog converting unit for receiving a pulse width modulation (PWM) signal, and transforming the PWM signal to a voltage signal; and a driving unit connected with the digital/analog converting unit in series for receiving the voltage signal, and providing a first predetermined voltage and a second predetermined voltage among which the first predetermined voltage is higher than the second predetermined voltage; wherein, the fan motor has a low constant rotation speed when the level of the voltage signal is higher than the first predetermined voltage level; the fan motor has a variable rotation speed when the level of the voltage signal is lower than the first predetermined voltage level but higher than the second predetermined voltage level; the fan motor has a high constant rotation speed when the level of the voltage signal is lower than the second predetermined voltage level.