Abstract: A power tool comprises a housing, a direct current motor arranged in the housing, a speed reduction mechanism coupled to a shaft of the motor, a tool head driven by the speed reduction mechanism, a first direct current power source, and a switching device. The motor comprises a common brush, a high speed brush and a low speed brush which are in sliding contact with a commutator. The switching device is configured to selectively connect the common brush and the high speed brush with the power source to operate the motor in a high speed mode and to connect the common brush and the low speed brush with the power source to operate the motor in a low speed mode.

Abstract: When the fan inserted in the fan header is a 4-pin fan, the control chip outputs PWM signals with different duty factors to the control pin of the fan header, to automatically change the rotary speed of the 4-pin fan. When the fan inserted in the fan header is a 3-pin fan, the control chip outputs the PWM signals whose duty factor changes with temperature of a chip under the fan to control the first power source to provide a voltage to the adjusting circuit. The adjusting circuit rectifies the voltage output from the first power source as an analog voltage signal to the control circuit. The control circuit controls the third power source to output a changeable driving voltage to the power pin of the fan header to control the rotary speed of the 3-pin fan.

Abstract: A commutation and velocity control system of a brushless DC motor receives a velocity command signal and provides command signals to drive the brushless DC motor. The system includes a summer that receives the velocity command signal and a velocity feedback signal and provides a velocity error signal indicative of the difference. A velocity loop compensator receives said velocity error signal and provides a compensated velocity error signal. A magnitude sensing circuit senses the magnitude of said compensated velocity error signal and provides a velocity magnitude signal indicative thereof. A polarity sensing circuit senses the polarity of the said compensated velocity error signal and provides a velocity polarity signal indicative thereof.

Abstract: The invention relates to an electric drive device with a DC motor (2) comprising a control circuit with an electronic commutator (3). The invention is characterized in that a derivation of a control signal (V_i_ref) is obtained from an induced motor voltage (E_sample) detected by a measuring device and from a reference value (V_i_av) which serves to regulate the speed of the DC motor (2), and in that the derived control signal (V_i_ref) serves to achieve a substantially constant torque of the DC motor (2) through adjustment of the motor currents (ia, ib, ic).

Abstract: A method and circuit design for establishing the operating status of a direct drive, multiple speed motor. More specifically, the invention furnishes a method for providing feedback to an air distribution system indicating first whether the system motor is operating and second which speed winding has been selected. The circuit design senses the voltage differences between the speed windings of the motor and also between the first speed motor winding and the power supply. The voltage difference sensed by the circuit will determine whether a light emitting diode (LED) illuminates. The illumination of the LED indicates to the system controller whether the motor is operating and the speed winding that has been selected, thus providing the necessary feedback to the air distribution system controller.

Abstract: A method and apparatus for operating a polyphase dc motor selectively in dual-coil or uni-coil commutation modes. The motor has a plurality of "Y" connected driving coils connected together at a center tap. Each driving coil has an input node at an end opposite the center tap, and is driven by a switch pair. Each switch pair is arranged for connection in series across a power supply voltage, and has a node between each switch connected to a respective one of the coil input nodes. An additional pair of switches are provided for connection in series across the power supply with a connection node between each switch connected to the center tap. A circuit is provided to operate the switches to cause a driving current to be passed between sequentially selected pairs of the driving coils for an initial start-up time.