CN102444603A - Fan control circuit - Google Patents

Abstract

A fan control circuit, including a triangular wave generating circuit, a temperature sensing circuit, a comparator and a switch circuit, the triangular wave generating circuit is connected to the positive input end of the comparator, and is used to output a triangular wave signal to the comparator , the temperature sensing circuit is connected to the inverting input end of the comparator, and is used to sense the ambient temperature and output a corresponding temperature signal to the comparator, and the comparator compares the magnitude of the triangular wave signal and the temperature signal, and outputs correspondingly A control signal is sent to the switching circuit to control the closing or opening of the switching circuit, and the switching circuit is connected between a power supply and a fan. The fan control circuit can reduce the load of the CPU.

Description

fan control circuit

technical field

The invention relates to a fan control circuit.

Background technique

At present, the cooling system inside the computer system generally uses the central processing unit to send a corresponding pulse width modulation signal to adjust the fan speed according to the temperature in the chassis. However, this method will increase the CPU load.

Contents of the invention

In view of the above, it is necessary to provide a fan control circuit that does not utilize a central processing unit, which can reduce the load on the central processing unit.

A fan control circuit, comprising a triangular wave generating circuit, a temperature sensing circuit, a first comparator and a switch circuit, the triangular wave generating circuit is connected to the positive input end of the first comparator, and is used to output a triangular wave signal To the first comparator, the temperature sensing circuit is connected to the inverting input terminal of the first comparator for sensing the ambient temperature and outputting a corresponding temperature signal to the first comparator, and the first comparator compares The magnitude of the triangular wave signal and the temperature signal are corresponding to output a control signal to the switch circuit to control the closing or opening of the switch circuit. The switch circuit is connected between a power supply and a fan.

The above-mentioned fan control circuit can control the speed of the fan according to the temperature of the chassis without using the CPU, thereby reducing the load on the CPU.

Description of drawings

FIG. 1 is a block diagram of a preferred embodiment of the fan control circuit of the present invention.

FIG. 2 is a circuit diagram of a first preferred embodiment of the fan control circuit in FIG. 1 .

3 is a first schematic diagram of the triangular wave signal generated by the triangular wave generating circuit in FIG. 2 and the control signal output by the comparator.

4 is a second schematic diagram of the triangular wave signal generated by the triangular wave generating circuit in FIG. 2 and the control signal output by the comparator.

FIG. 5 is a circuit diagram of a second preferred embodiment of the fan control circuit in FIG. 1 .

Description of main component symbols

Triangular wave generating circuit 10, 10'

Temperature sensing circuit 12, 12’

Comparators 11, U1, U1’, U2, U2’, U3, U3’

Switch circuit 15, 15’

fan 20

Power supply 30, Vcc

Resistors R1, R1’, R2, R2’, R3, R3’, R4, R4’, R5,

        R5’, R6, R6’, R7, R7’, R8, R9, R10

Capacitor C1, C1’, C2, C2’

Transistor Q1, Q1’, Q2, Q2’, Q3, Q3’

Detailed ways

Below in conjunction with accompanying drawing and preferred embodiment the present invention is described in further detail:

Please refer to FIG. 1 , a preferred embodiment of the fan control circuit of the present invention includes a triangular wave generating circuit 10 , a temperature sensing circuit 12 , a comparator 11 , a switching circuit 15 and a power supply 30 .

The triangular wave generating circuit 10 is connected to the positive input terminal of the comparator 11 for outputting a triangular wave signal to the comparator 11 .

The temperature sensing circuit 12 is connected to the inverting input terminal of the comparator 11 for sensing ambient temperature and outputting a corresponding temperature signal to the comparator 11 . The comparator 11 compares the triangular wave signal and the temperature signal, and outputs a control signal to the switch circuit 15 correspondingly.

The switch circuit 15 is connected between the power supply 30 and the fan 20 , and closes or disconnects the connection between the power supply 30 and the fan 20 according to the control signal, thereby correspondingly controlling the working state of the fan 20 .

Please refer to FIG. 2 , in the first preferred implementation of the fan control circuit, the triangular wave generating circuit 10 includes two comparators U2 , U3 and an NPN transistor Q1 . The positive input terminal of the comparator U2 is grounded, the negative input terminal is connected with the output terminal of the comparator U2 through a capacitor C1, and connected with the output terminal of the comparator U3 through a resistor R1, the power supply of the comparator U2 The terminal is connected to the power supply Vcc (that is, the power supply 30 above), the ground terminal is grounded, the output terminal is connected to the positive input terminal of the comparator U3 through a resistor R2, and the positive input terminal of the comparator U3 is also connected to the output terminal through the resistor R3. terminal, the inverting input terminal of the comparator U3 is grounded, the power supply terminal is connected to the power supply Vcc, and the ground terminal is grounded. The output terminal of the comparator U3 is also connected to the base of the NPN transistor Q1 through the capacitor C2 and the resistor R4 in turn, the base of the NPN transistor Q1 is also connected to the power supply Vcc through the resistor R5, the emitter is grounded, and the collector is connected through the resistor R6 Connect with the power supply Vcc. The collector of the NPN transistor Q1 is also used as the output terminal of the triangular wave generating circuit 10 and connected to the positive input terminal of the comparator U1 (ie 11 in FIG. 1 ).

The temperature sensing circuit 12 includes a resistor R7 and a positive temperature coefficient thermistor PTC, the power supply Vcc is connected to the inverting input terminal of the comparator U1 through the resistor R7, one end of the positive temperature coefficient thermistor PTC is grounded, and the other One end is connected between the inverting input end of the comparator U1 and the resistor R7. The ground end of the comparator U1 is grounded, and the power end is connected to the power supply Vcc.

The switch circuit 15 includes a PNP transistor Q2, the emitter of the PNP transistor Q2 is connected to the power supply Vcc, the base is connected to the output terminal of the comparator U1 through a resistor R8, and the collector is connected to the fan 20 .

The working principle of the fan control circuit in Figure 2 will be described below:

The triangular wave generating circuit 10 generates a fixed triangular wave signal, shown as Tri in FIG. 3 and FIG. 4 , and the triangular wave signal is output to the comparator U1.

Assuming that the temperature inside the chassis is high at this time, according to the characteristics of the positive temperature coefficient thermistor PTC, the resistance value of the positive temperature coefficient thermistor PTC is relatively high at this time, so that the power supply Vcc is output to the comparator U1 after voltage division. The voltage value (that is, the “temperature signal” above) is relatively high, as shown by the voltage value Va in FIG. 3 .

According to the working principle of the comparator U1, when the voltage at its positive input terminal is higher than the voltage at its negative input terminal, its output terminal outputs a high-level signal. Conversely, when the voltage at its positive input terminal is lower than the voltage at its inverting input terminal, its output terminal outputs a low-level signal. Therefore, the comparator U1 outputs a control signal shown as PWM-OUT1 in FIG. 3 , which has a first duty cycle.

Assuming that the temperature inside the chassis is low at this time, according to the characteristics of the positive temperature coefficient thermistor PTC, the resistance value of the positive temperature coefficient thermistor PTC is relatively low at this time, so that the power supply Vcc is output to the comparator U1 after voltage division. The voltage value (that is, the “temperature signal” above) is relatively low, as shown by the voltage value Vb in FIG. 4 . Therefore, the comparator U1 outputs a control signal shown as PWM-OUT2 in FIG. 4 , which has a second duty cycle. Apparently, the first duty ratio is smaller than the second duty ratio. According to the duty ratio of the control signal, the fan 20 rotates at a higher temperature than the fan 20 when the cabinet temperature is low.

The above-mentioned fan control circuit can make the rotating speed of the fan 20 lower when the temperature in the cabinet is low, and the rotating speed of the fan 20 be higher when the temperature in the cabinet is higher without using the central processing unit, thereby reducing the operating speed of the central processing unit. load.

Please refer to FIG. 5, the difference between the second preferred embodiment of the fan control circuit and the first preferred embodiment is that in the second preferred embodiment, the temperature sensing circuit 12' includes a resistor R7' and a negative temperature coefficient thermistor NTC, the switch circuit 15' includes a PNP transistor Q2' and an NPN transistor Q3, the output terminal of the comparator U1' is connected to the base of the NPN transistor Q3 through a resistor R8', the emitter of the NPN transistor Q3 is grounded, and the collector is passed through The resistor R9 is connected to the power supply Vcc, and is also connected to the base of the PNP transistor Q2' through the resistor R10. The emitter of the PNP transistor Q2' is connected to the power supply Vcc, and the collector is connected to the fan 20.

The principle of the fan control circuit in FIG. 2 is the same. When the temperature in the chassis is different, the comparator U1 will output control signals with different duty ratios, so as to control the switch circuit 15' to have a corresponding working state, so that the fan 20 can The speed is slower when the temperature is low, and the speed is faster when the temperature is higher.

Claims (6)

1. A fan control circuit, comprising a triangular wave generating circuit, a temperature sensing circuit, a first comparator and a switch circuit, the triangular wave generating circuit is connected with the positive input end of the first comparator for outputting a The triangular wave signal is sent to the first comparator, and the temperature sensing circuit is connected to the inverting input terminal of the first comparator for sensing the ambient temperature and outputting a corresponding temperature signal to the first comparator, the first comparator The device compares the magnitude of the triangular wave signal and the temperature signal, and correspondingly outputs a control signal to the switch circuit to control the closing or opening of the switch circuit. The switch circuit is connected between a power supply and a fan. 2. The fan control circuit according to claim 1, wherein the temperature sensing circuit comprises a voltage dividing resistor and a positive temperature coefficient thermistor, one end of the voltage dividing resistor is connected to the power supply, and the other end is connected to the The inverting input terminal of the first comparator is connected, one end of the positive temperature coefficient thermistor is grounded, and the other end is connected between the inverting input terminal of the first comparator and the voltage dividing resistor. 3. The fan control circuit according to claim 2, wherein the switch circuit comprises a first PNP transistor, the emitter of the first PNP transistor is connected to the power supply, and the base is compared with the first resistor through a first resistor. connected to the output of the device, and the collector is connected to the fan. 4. The fan control circuit according to claim 1, wherein the temperature sensing circuit comprises a voltage dividing resistor and a negative temperature coefficient thermistor, one end of the voltage dividing resistor is connected to the power supply, and the other end is connected to the The inverting input terminal of the first comparator is connected, one end of the negative temperature coefficient thermistor is grounded, and the other end is connected between the inverting input terminal of the first comparator and the voltage dividing resistor. 5. The fan control circuit according to claim 4, wherein the switch circuit comprises a first PNP transistor and a first NPN transistor, and the output terminal of the first comparator communicates with the first NPN transistor through a first resistor. The base of the transistor is connected, the emitter of the first NPN transistor is grounded, the collector is connected with the power supply through a second resistor, and is also connected with the base of the first PNP transistor through a third resistor, and the first PNP transistor is connected to the base. The emitter is connected to the power supply, and the collector is connected to the fan. 6. The fan control circuit according to claim 1, wherein the triangular wave generating circuit comprises a second comparator, a third comparator and an NPN transistor, the positive input terminal of the second comparator is grounded, The inverting input terminal is connected to its output terminal through a first capacitor, and is also connected to the output terminal of the third comparator through a first resistor, and the output terminal of the second comparator is connected to the third comparator through a second resistor The positive input terminal of the third comparator is connected to the positive input terminal of the third comparator, the positive input terminal of the third comparator is also connected to the output terminal of the third comparator, the negative input terminal of the third comparator is grounded, and the output terminal of the third comparator is also connected to Connect to the base of the NPN transistor through a second capacitor and a fourth resistor, the base of the NPN transistor is also connected to the power supply through a fifth resistor, the emitter is grounded, and the collector is connected to the power supply through a sixth resistor , the collector of the NPN transistor is also used as the output terminal of the triangular wave generating circuit and connected to the positive input terminal of the first comparator.

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