This application incorporates by reference Taiwan application Serial No. 090125720, filed Oct. 17, 2001.
1. Field of the Invention
This invention relates in general to a controlling device for a motor. More particularly, the invention relates to a controlling device for a motor capable of being driven by an AC power source or a DC power source.
2. Description of Related Art
A conventional AC (alternative current) fan uses an AC power source as its working power source, so that the coil wiring of the stator or the rotor is to form an induced magnetic field to operate the motor. However, since the rotational speed of the motor is proportional to the frequency of the AC power source, the rotational speed of the motor cannot be increased due to too low frequency of the AC power source. For some situations requiring a high wind flow, the motor cannot increase its rotational speed because the conventional fan""s motor uses the AC power source. The formula of fan speed expressed as follow: r.p.m.=(N*f/2)*(60 sec.), wherein r.p.m. is the round-per-minute speed, N is the pole of wirings, and f is the frequency of AC power source.
Conventionally, in order to obtain a high wind flow by using the AC motor, multiple motor sets are combined to achieve an output of high wind flow. An alternative method is to increase the number of pole wirings within the AC motor, so that the motor""s rotational speed is increased to arise the wind flow. However, to increase the number of pole wirings is not only that the coil wirings are very difficult, but the motor""s manufacturing cost is also increased. Therefore, these solutions do not meet the economic requirements.
In addition to the above defects, the inductance of coil is always in an high impedance if the fan working in AC mode, which is because the current of coil is alternatively changed. The working current of the AC motor can be expressed as followed.
I=V/Zxe2x80x83xe2x80x83(1)
Where I is the working current of the AC motor, V is the voltage provided by the power source, and Z is the impedance of the coil. From the formula (1), the impedance Z of the coil is expressed below.
Z={square root over (R2+XL2)}xe2x80x83xe2x80x83(2)
where XL is an AC inductance, XL=2xcfx80f L. Therefore, when the motor coil is from the static status to the operation status, it needs a sufficient current to make the coil to create a sufficient starting torque. In addition, the current is proportional to the voltage, and therefore, the starting voltage for the motor is also very high. Accordingly, the low voltage characteristic of the AC motor is very worse. Moreover, when the conventional AC motor is locked, because no break protection device, the temperature increases will damage the fan.
As a result, for the current fan using the AC motor, its rotational speed, starting up approach, protection device and manufacturing cost are restricted by the AC power source, and therefore cannot overcome the aforementioned defects. Therefore, to further improve the AC motor structure is demanded.
In light of the foregoing description, it is an object of the present invention is to provide a motor controlling device, wherein an AC power source is used and the rotational speed of the motor of the fan can be effectively increased.
According to the object(s) mentioned above, the present invention provides a motor controlling device for an AC/DC driven motor. This controlling device is used for an AC/DC driven motor. The motor comprises plural coils, and the motor controlling device comprises an AC/DC converting unit, a voltage stabilizing unit, a phase detecting/controlling unit, and a high voltage driving unit. The AC/DC converting unit is inputted an AC power source to convert the AC power source into a high voltage DC voltage. The voltage stabilizing unit is coupled to the AC/DC converting unit, for receiving the high voltage DC voltage to convert it into a low voltage DC voltage. The phase detecting/controlling unit is coupled to the motor and the voltage stabilizing unit, for receiving the low voltage DC voltage as a work voltage, and for detecting a polarity of the permanent magnet to output a first detecting and a second detecting signals accordingly, so as to provide a shut down protection when the motor is locked. The high voltage driving unit is coupled to the AC/DC converting unit, the phase detecting/controlling unit, and the motor, for receiving the high voltage DC voltage as a work voltage, and for receiving the first detecting and the second detecting signals to output accordingly a first driving and a second driving signals so as to drive the motor.