Abstract: A discharge protection circuit for discharging a full-bridge circuit in a brushless DC fan, wherein the brushless DC fan comprises a control circuit outputting at least one first control signal and at least one second control signal to the full-bridge circuit. The second control signal is a reverse signal of the first control signal; and the full-bridge circuit comprises a first impedance, a second impedance and a switch. The switch has a first terminal, a second terminal, and a third terminal that is grounded. The first terminal and the first impedance are in series connection for receiving the first control signal to control the status of the switch. The second terminal and the second impedance are in series connection and are connected to the input terminal of the second control signal of the full-bridge circuit, and the full-bridge circuit is discharged according to the status of the switch.

Abstract: A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.

Abstract: A fan motor speed control circuit includes a driving circuit, a voltage division circuit, and a speed modulator. The voltage division circuit has a first transistor and a plurality of resistors and is connected between a voltage source and the driving circuit. The speed modulator has a second transistor and a plurality of parallel resistors and is connected between the voltage division circuit and the driving circuit. The current of the fan motor speed control circuit flows through a first path under a first input voltage generated from the voltage source and through a second path under a second input voltage larger than the first one; the parallel resistors are in the second path such that the current value passing through the driving circuit varies according to the resulting resistance value of the parallel resistors.

Abstract: A fan speed control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a phase compensation unit. The PWM signal generating circuit generates a PWM control signal with a sequence of alternating on-time and off-time, and the driving circuit outputs a driving signal according to the PWM control signal to a fan motor. The phase compensation unit is connected to the fan motor for delaying or advancing the PWM control signal by a phase angle to synchronize the acting period of the back electromotive force formed by the magnetic flux variation with the off-time of the PWM control signal.

Abstract: A thermal control variable-speed circuit without switching noise is connected with a driving circuit, which controls the rotation speed of a fan motor using a driving voltage. The thermal control variable-speed circuit includes a reference voltage output circuit and a driving voltage control circuit. The reference voltage output circuit outputs a corresponding reference voltage signal according to ambient temperature changes. The reference voltage output circuit has one end connected to a first resistor in series and to a second resistor in parallel. The driving voltage control circuit outputs a corresponding driving voltage according to the magnitude of the reference voltage signal.

Abstract: A circuit board adapted to a fan comprises a circuit region and a heat-dissipative film. The circuit region is provided on a first surface of the circuit board and comprises at least one heat-generating component thereon. The heat-dissipative film is coated on an edge portion of the first surface and is in contact with the heat-generating component. A plurality of openings through the heat-dissipative film, a protrusion of the circuit board, a cutout in the protrusion to expose the heat-generating component to airflow, etc., have been disclosed and claimed for enhancing the efficiency in heat dissipation. A heat sink may also be provided on a second surface opposite to the first surface of the circuit board. The heat sink is connected to the heat-dissipative film to help dissipate the heat generated by the operation of the fan.