Fan system with hysteresis character and method thereof

Abstract

A fan system includes a fan, a hysteresis circuit including a temperature sensor, a first operational amplifier having a negative input end coupled to the temperature sensor, and a second operational amplifier having a negative input end coupled to an output end of the first operational amplifier and having a positive input end coupled to a power supply for outputting a first voltage when the temperature sensed by the temperature sensor is greater than a first temperature, and for outputting a second voltage when the temperature sensed by the temperature sensor is lower than a second temperature. The fan system further includes a fan switch coupled to the hysteresis circuit and the fan for controlling a rotational speed of the fan according to the first voltage or the second voltage outputted from the hysteresis circuit. The first temperature is greater than the second temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagram of a fan switch corresponding to temperature of a conventional display card.

FIG. 2 illustrates a functional block diagram of an interface capable of controlling fan rotational speed according to temperature change.

FIG. 3 illustrates a circuit diagram explaining operation of a hysteresis circuit, a fan switch, and a fan according to one embodiment of the present invention.

FIG. 4 illustrates a graph of interface temperatures corresponding to switching rotational speeds and a graph of interface temperatures corresponding to on and off of a fan.

FIG. 5 illustrates a diagram of a hysteresis circuit according to another embodiment of the present invention.

FIG. 6 illustrates a relationship diagram of Vin and Vout corresponding to the hysteresis circuit of FIG. 5.

FIG. 7 illustrates a relationship diagram of inputting voltage and outputting voltage of a hysteresis circuit according to another embodiment of the present invention.

Claims

1. A fan system with hysteresis character, the fan system comprising: a fan;a hysteresis circuit comprising: a temperature sensor;a first operational amplifier having a first negative input end coupled to the temperature sensor and a first output end; anda second operational amplifier having a second negative input end coupled to the first output end and having a second positive end coupled to a first power supply for outputting a first voltage when the temperature sensed by the temperature sensor is greater than a first temperature, and for outputting a second voltage when the temperature sensed by the temperature sensor is lower than a second temperature and a second output end; anda fan switch coupled to the hysteresis circuit and the fan for controlling a rotational speed according to the first voltage or the second voltage outputted by the hysteresis circuit;wherein the first temperature is greater than the second temperature.

2. The fan system of claim 1 wherein when power level of a first positive input end is greater than power level of the first negative input end, the first output end is open, and when power level of the second positive input end is higher than the power level of the second negative input end, the second output end is open.

3. The fan system of claim 1 wherein the hysteresis circuit further comprises a pull-high resistor coupled to the second output end and a second power supply for enhancing the voltage of the fan switch when the second output end is open.

4. The fan system of claim 1 wherein the temperature sensor is a negative temperature coefficient heat sensitive conductance.

5. The fan system of claim 1 wherein the fan system comprises: a bipolar junction transistor comprising an emitter, a collector, and a base, the emitter being coupled to a third power supply, and the collector being coupled to the fan; anda metal-oxide semiconductor (MOS) comprising a source, a drain, and a gate, the drain being coupled to the base of the bipolar junction transistor, the source being coupled to a ground end, and the gate being coupled to the hysteresis circuit for receiving voltage signals transmitted from the hysteresis circuit in order to control on and off of the bipolar junction transistor.

6. The fan system of claim 5 wherein the fan switch further comprises a resistor, an end of the resistor coupled to the fan, another end of the resistor coupled to the third power supply that is also coupled to the emitter of the bipolar junction transistor.

7. The fan system of claim 5 wherein the fan system further comprises a capacitance coupled to the collector of the bipolar junction transistor for storing electric charge supplied to rotate the fan.

8. An interface capable of controlling fan speed according to temperature change, the interface comprising: at least one electronic component, the electronic component generating different temperatures according operation condition;a fan:a hysteresis circuit, comprising: a temperature sensor coupled to the electronic component;a first operational amplifier having a first negative input end coupled to the temperature sensor and a first output end; anda second operational amplifier having a second negative input end coupled to the first output end, and a second positive input end coupled to a first power supply for outputting a first voltage when the temperature sensed by the temperature sensor is greater than a first temperature, and for outputting a second voltage when the temperature sensed by the temperature sensor is lower than a second temperature and a second output end; anda fan switch coupled to the hysteresis circuit and the fan, the fan switch is utilized for controlling the fan speed according to the first voltage or the second voltage outputted by the hysteresis circuit;wherein the first temperature is greater than the second temperature.

9. The interface of claim 8 wherein the temperature sensor is a negative temperature coefficient heat sensitive conductance.

10. The interface of claim 8 wherein the fan switch comprises: a bipolar junction transistor comprising an emitter, a collector, and a base, the emitter being coupled to a third power supply, and the collector being coupled to the fan; anda metal-oxide semiconductor (MOS) comprising a source, a drain, and a gate, the drain being coupled to the base of the bipolar junction transistor, the source being coupled to a ground end, and the gate being coupled to the hysteresis circuit for receiving voltage signals transmitted from the hysteresis circuit in order to control on and off of the bipolar junction transistor.

11. The interface of claim 10 wherein the fan switch further comprises a resistor, an end of the resistor coupled to the third power supply that is also coupled to the emitter of the bipolar junction transistor.

12. The interface of claim 10 wherein the fan switch further comprises a capacitance coupled to the collector of the bipolar junction transistor for storing electric charge supplied to rotate the fan.

13. The interface of claim 10 wherein the interface is a display interface.

14. A method of controlling fan speed according to temperature detected, the method comprising the following steps: controlling the fan to switch from a first speed to a second speed when the temperature sensed rises from below a first temperature to the first temperature; andcontrolling the fan to switch from the second speed to a third speed when the temperature sensed falls from above a second temperature to the second temperature;wherein the first temperature is greater than the second temperature.

15. The method of claim 14 wherein the second speed is greater than the first speed, and the second speed is greater than the third speed.

16. The method of claim 14 wherein the first speed and the third speed are zero.