KR20000017630U - Pwm control circuit for a dc brushlesss fan - Google Patents

Abstract

A rectifier circuit for rectifying a voltage signal representative of the rotational speed of the fan, a comparator for comparing the rectified voltage signal to a reference voltage signal, and a DC brushless ) A PWM control circuit for the fan is provided, and the rotational speed of the fan can be controlled and maintained at a constant value.

A reference voltage signal is generated by a voltage divider formed by a thermistor and a resistor so that the rotational speed of the fan can be adjusted as the temperature of the working environment changes.

Description

[0001] The present invention relates to a PWM control circuit for a DC brushless fan,

The present invention relates generally to a PWM (Pulse Width Modulation) control circuit for a DC (direct current) brushless fan, and more particularly to a speed control circuit for a DC brushless fan.

A typical DC brushless fan has only two terminals, namely a source terminal and a ground terminal, which have been commonly used in some circumstances when the requirements regarding the rotational speed of the fan are not strict.

However, when a DC brushless fan is used for dissipation of a power supply or microprocessor chip that typically generates significant heat, the operating state of the fan is observed and controlled to effectively facilitate heat dissipation do.

To prevent damage to electronic components due to insufficient heat dissipation, a " third terminal " of a DC brushless fan has been utilized. That is, a third terminal (so-called signal detection terminal) extending from the internal control circuit of the fan is utilized.

By using the third terminal of the DC brushless fan, it is possible to detect a rectangular wave signal which is synchronous with the fluctuation of the rotation speed of the fan and to connect to an external circuit.

The purpose of this invention is to provide a PWM control circuit to the DC brushless fan to control the rotational speed of the fan and to maintain it at a constant value.

Another purpose of the present invention is to provide a PWM control circuit in a DC brushless fan to adjust the rotational speed of the DC brushless fan as the temperature of the working environment changes, thereby achieving optimum heat dissipation .

1 is a schematic block diagram illustrating a PWM control circuit for a DC brushless fan according to the present invention;

Figure 2 is a detailed circuit diagram of the PWM control circuit of Figure 1;

3 is a diagram showing a voltage signal output from a switching element of a PWM control circuit according to the present invention;

4 is a characteristic diagram of a rectifier circuit of another PWM control circuit in the present invention.

According to one aspect of the present invention, a PWM control circuit for a DC brushless fan includes a rectifier circuit, a comparator, and a switching device, wherein the rectifier circuit receives a square wave signal from the fan, Compares the rectified DC voltage signal to a reference voltage signal, and the switching element is repeatedly closed and opened according to the comparison result from the comparator.

According to another aspect of the present invention, a reference voltage signal is generated by a voltage divider formed of a resistor and a thermistor connected in series between the ground and source voltages.

Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

1, the PWM control circuit 1 for the DC brushless fan 50 includes a rectifier circuit 10, a comparator 20, and a switching element 30. The rectifier circuit 10 includes a rectifier circuit 10, a comparator 20, The fan 50 to be controlled is provided with a source terminal V +, a ground terminal G and a signal detection terminal T.

1, the input terminal of the rectifying circuit 10 is connected to the signal detecting terminal T of the fan 50, and the output terminal of the rectifying circuit 10 is connected to the inverted input terminal of the comparator 20. [ The rectifying circuit 10 receives a continuous square wave signal from the fan 50 which indicates the rotational speed of the fan 50 and transmits the rectified and filtered DC voltage signal V1 to the comparator 20. [

The non-inverted input terminal of the comparator 20 is connected to the reference voltage signal V _ref which is used to set the rotational speed of the fan 50 and the output terminal of the comparator 20 is connected to the switching element 30 . The comparator 20 compares the current DC voltage signal V1 from the rectifying circuit 10 with the reference voltage signal V _ref and transmits a signal to control the switching element 30 according to the comparison result.

The switching element 30 is three terminal elements, for example, the switching element 30 is formed by an electronic switch such as a transistor. The switching element 30 is connected in series between the source voltage Vcc and the source terminal V + of the fan 50 and the third terminal (control terminal) of the switching element 30 is connected to the output terminal of the comparator 20 .

The operation of the switching element 30 depends on the comparison result of the rectified DC voltage signal V1 outputted from the rectifying circuit 10 and the reference voltage signal V _ref .

When the DC voltage signal V1 output from the rectifier circuit 10 is lower than the reference voltage signal V _ref , that is, when the rotational speed of the fan 50 is lower than its set value, the comparator 20 switches the logical high value And outputs it to the element 30. The switching element 30 is then closed and the fan 50 is powered on. Thus, the rotational speed of the fan 50 is increased.

In contrast, when the DC voltage signal V1 output from the rectifying circuit 10 is higher than the reference voltage signal _Vref , that is, when the rotational speed of the fan 50 is higher than its setting value, And outputs a low value to the switching element 30. Then, the switching element 30 is opened, and the fan 50 is powered off. Thus, the rotational speed of the fan 50 is reduced.

In operation, the switching element 30 is repeatedly closed and opened as the rotational speed of the fan changes, and the fan 50 is intermittently powered on, so that the rotational speed of the fan 50 is controlled to be maintained at a constant value .

3, the output signal V2 of the switching element 30 is a rectangular wave. Here, the width TIME ON represents the period during which the switching element 30 is closed, and the width TIME OFF represents the period during which the switching element 30 is closed. Lt; / RTI > is open. According to the above description of FIG. 1, the widths TIME ON and TIME OFF are modulated to control the rotational speed of the fan 50.

In Fig. 2, the detailed circuit for implementing the rectifying circuit 10 of Fig. 1 is described as follows. In the rectifying circuit 10, the DC voltage component of the detected spherical signal from the terminal T of the fan 50 is isolated by the capacitor 11. The signal detected without the DC voltage component is then rectified by two diodes 12 and 13 acting as a half-wave rectifier and filtered by an RC filter formed of a resistor 14 and a capacitor 15.

Thus, the detected signal from the fan 50 can be converted to a rectified and filtered DC voltage signal V1, which is applied to the rotational speed n of the fan 50 (as shown in FIG. 4) It is proportional.

2, a reference voltage signal V _ref is generated by a voltage divider formed by a NTC (negative temperature coefficient) thermistor 40 and a resistor 42 connected in series between a source voltage Vcc and a ground fault.

When the temperature of the working environment increases, the resistance of the NTC thermistor 40 decreases, so that the divided reference voltage signal V _ref is increased. That is, the setting value of the rotational speed of the fan 50 increases as the temperature of the working environment increases.

In contrast, the setting value of the rotational speed of the fan 50 is reduced as the temperature of the working environment decreases.

As the NTC thermistor 40 aids in the temperature compensating role, the rotational speed of the DC brushless fan 50 can be adjusted as the temperature of the working environment changes, so that optimal heat dissipation can be achieved.

In another embodiment (not shown), if no temperature compensation is required, the reference voltage signal V _ref can simply be generated by a voltage divider formed by two resistors connected in series between the source voltage Vcc and ground GND .

While the present invention has been described with reference to certain preferred embodiments, it is understood that various modifications, substitutions and alterations can be made by those skilled in the art within the spirit and scope of the present invention as defined by the appended claims.

Claims (12)

A PWM control circuit for a DC brushless fan provided with a source terminal, a ground terminal, and a signal detection terminal, A rectifying circuit for receiving a voltage signal from the signal detecting terminal of the fan and generating a rectified DC voltage signal, A comparator for comparing the rectified DC voltage signal with a reference voltage signal, And a switching element that is opened when the rectified DC voltage signal is lower than the reference voltage signal and is open when the rectified DC voltage signal is higher than the reference voltage signal, The fan is intermittently powered on, and the rotational speed of the fan is controlled and maintained at a constant value. The method according to claim 1, Wherein the rectifying circuit comprises a half-wave rectifier. 3. The method of claim 2, Wherein the half-wave rectifier is formed of two diodes. The method according to claim 1, Wherein the rectifying circuit further comprises an RC filter. 5. The method of claim 4, Wherein the RC filter is formed of a resistor and a capacitor. The method according to claim 1, Wherein the rectifier circuit further comprises a capacitor isolating a DC voltage component present in the received voltage signal. The method according to claim 1, Wherein the reference voltage signal is generated by a voltage divider. 8. The method of claim 7, Wherein the voltage divider is formed of a thermistor and a resistor. 8. The method of claim 7, And the voltage divider is formed of two resistors. The method according to claim 1, Wherein the comparator is formed of an operational amplifier. The method according to claim 1, Wherein the switching element is an electronic switch. 12. The method of claim 11, Wherein the switching element is formed of a transistor.