CN1073757C - DC brushless fan detection circuit - Google Patents

Abstract

The invention relates to a direct current brushless fan detection circuit, which comprises a circuit formed by a Hall sensor, two transistors and two magnetic field coils, and is characterized in that: the second transistor and the second magnetic field coil are connected with a loop formed by serially connecting a capacitor and a resistor, and a circuit is led out to the gate of a field effect transistor powered by a voltage source different from the power supply of the fan, and a signal detection lead is led out from the drain of the field effect transistor, so that the level of a detection signal can be adjusted by changing the voltage of the field effect transistor, and the fan is enabled to be in a specific level when the fan stops running due to faults, thereby not only widening the range of the detection signal, but also making the detection of the faults of the fan more definite.

Description

DC brushless fan detection circuit

The invention relates to a fan detection circuit, in particular to a small DC brushless fan which can be used for heat dissipation of power supplies, computers and microcomputer chips, and has the ability to adjust the detection signal level range and detect fan failures. Fan detection circuit.

In terms of the internal control circuit of the small-sized DC brushless fan in the prior art, as shown in FIG. Two magnetic field coils L1 and L2 connected in series on the transistors 10 and 20 are jointly composed. Using the corresponding relationship of the loop, when the power is turned on, the transistor 10 is first turned on and the magnetic field coil L1 is powered, and the magnetic field coil L1 The generated magnetic field is magnetic due to the effect of homosexual repulsion so that the fan blade rotor provided with the magnetic field rotates, and then the Hall sensor 40 senses the change of the magnetic field of the rotor rotation, thereby sending a high-level signal to make the transistor 10 that was turned on originally Turn off, turn on another transistor 20 and another magnetic field coil L2, and the magnetic field coil L2 generates the same magnetic field as the fan blade rotor, and pushes the fan blade rotor to continue to rotate, so that the alternate conduction and generation The alternating magnetic field makes the blade rotor run continuously.

However, the internal control circuit of the above-mentioned fan is only for the operation of the fan. As to whether the fan itself is operating and the speed is normal, because it only has a power input terminal and there is no other situation for detecting the fan operation signal, there is no way to know. As we all know, When the fan is running continuously, it is easy to cause unstable speed or even stop completely due to factors such as wear or circuit instability or failure. This is very likely to cause components to Abnormal work or even burning, obviously does not meet the actual requirements, therefore, there is a signal line obtained by pulling out a signal line from the base or collector of the aforementioned first and second transistors 10, 20 to obtain a frequency that is proportional to the rotation speed of the fan. Proportional square wave signal, according to this signal, the internal operation of the fan can be known and used as detection and warning (such as external light detection circuit, sound detection circuit, frequency counting circuit or speed control circuit, etc.). It can achieve the purpose of detecting the operation of the fan, but because the level of the derived signal is limited by the voltage of the fan power supply, it cannot be adjusted according to actual needs, and when the fan fails, the detected signal level depends on the Depending on the position of the blade rotor, the level may be high or low, and the output signal level when the fan fails cannot be predicted. Therefore, the application of the detected signal is often limited, and it is necessary to improve it.

The purpose of the present invention is to provide an improved DC brushless fan detection circuit, which can adjust the detection signal level range and detect fan failure, and make the detection signal of the fan more convenient and more in line with actual needs.

Another object of the present invention is to provide an improved DC brushless fan detection circuit, which can adjust the detection signal level range, and can flexibly adjust the size of the external voltage source Vcc according to the needs of practical applications to obtain the required The detection signal level range enables the fan detection signal to have a wider range of applications.

Another object of the present invention is to provide an improved DC brushless fan detection circuit, which can clearly detect whether the fan is faulty or not.

The purpose of the present invention is achieved like this:

A DC brushless fan detection circuit, including a DC brushless fan control circuit composed of a Hall sensor, two transistors and two magnetic field coils, is characterized in that:

Between the junction of the second transistor and the second magnetic field coil and the grounding point, a loop connected in series with a capacitor and a resistor is connected across the loop, and at the same time, a line is drawn from the junction of the capacitor and the resistor to The gate of a field effect transistor powered by a voltage source different from the fan power supply is used to control the action of the field effect transistor, and a signal detection wire is drawn from the drain of the field effect transistor for detecting the fan operating conditions and detect fan failures.

In the above brushless DC fan detection circuit, a diode is connected in series between the junction of the capacitor and the resistor and the gate of the field effect transistor, and a diode is connected in series with the gate of the field effect transistor. A second capacitor is connected to the ground at the junction of the poles to provide a detection method for rotation detection.

In the detection circuit of the brushless DC fan mentioned above, the field effect transistor is an N-channel enhancement metal oxide semiconductor field effect transistor.

The present invention has the following advantages due to the adoption of the above-mentioned technical scheme:

1. Since a loop connected in series with a capacitor and a resistor is bridged between the junction of the second transistor and the second magnetic field coil and the ground point, and a circuit is drawn from the junction of the capacitor and the resistor To the gate of a field effect transistor powered by a voltage source different from the fan power supply to control the action of the field effect transistor, and a signal detection wire is drawn from the drain of the field effect transistor, so its detection The level of the output signal can be adjusted and set according to actual needs without being limited by the power supply voltage of the fan, and the detected signal is a square wave signal whose frequency is proportional to the fan rotation speed when the fan is running normally , and when the fan fails, it will always present a specific potential (such as high level), so it can not only detect the fan's operation, but also clearly know whether the fan is faulty, and make the detection signal of the fan more convenient and convenient. It is more in line with actual needs.

2. Since the junction of the second transistor of the internal control circuit of the fan and the second magnetic field coil is grounded with a capacitor connected in series with a resistor to form an RC circuit type, and the signal at the junction of the resistor and capacitor is drawn out as It is the input of the gate (Gate) of a Field Effect Transistor (FET) to control the switch of the Field Effect Transistor, and the Field Effect Transistor is pulled up by an external voltage source Vcc different from the fan power supply. The resistor (Pull-Up Resistor) is powered, and the drain (Drain) of the field effect transistor forms a signal detection point, which can be connected to a signal detection wire to the outside world, because the RC circuit and the field effect transistor Therefore, the potential of the detected signal depends on the voltage source Vcc and is not limited by the fan power supply voltage, so the Vcc can be flexibly adjusted according to the needs of practical applications to obtain the required detection signal level range , so that the fan detection signal can have a wider range of applications.

3. Since the signal of the signal detection wire presents a square wave signal whose frequency is proportional to the rotation speed of the fan when the fan is operating normally, and remains at a specific level (such as a high level) when the fan fails, so , which can achieve the purpose of clearly knowing whether the fan is faulty or not by the level of the signal detection wire.

It can be seen that the present invention not only greatly improves the detection capability of the fan signal, but also makes the detection of the fan fault clearer, so that the design of the fan signal detection is more in line with the actual needs.

Through the following description of an embodiment of the brushless DC fan detection circuit of the present invention combined with the accompanying drawings, the purpose, structural features and advantages of the present invention can be further understood. Among them, the attached figure is:

FIG. 1 is an electrical schematic diagram of a DC brushless fan detection circuit proposed according to the present invention.

Fig. 2 is an output waveform diagram of the signal detection wire in the detection circuit of the brushless DC fan proposed by the present invention when the fan is in normal operation.

3A is an output waveform diagram of the signal detection wire when the fan is faulty and does not run in the detection circuit of the brushless DC fan according to the present invention, but the junction of the second transistor and the second coil is at a low level.

3B is an output waveform diagram of the signal detection wire when the second transistor and the second coil connect the second transistor and the second coil in the detection circuit of the brushless DC fan proposed by the present invention and the fan is not running.

FIG. 4 is a waveform diagram of signal detection wire output when detecting changes in fan speed in the DC brushless fan detection circuit according to the present invention.

Fig. 5 is an electrical schematic diagram for the application of rotation detection (Rotation Detection) in the DC brushless fan detection circuit proposed according to the present invention.

Fig. 6 is an output waveform diagram of a signal detection wire used as a rotation detection (Rotation Detection) application in the DC brushless fan detection circuit proposed according to the present invention.

Fig. 7 is an electrical schematic diagram of a brushless DC fan in the prior art.

As shown in Figure 1, the internal control circuit of the fan of the present invention also forms a basic circuit with a Hall sensor 40, two transistors 10, 20 and two magnetic field coils L1, L2, and the design of the detection circuit of the present invention is to The junction of the second transistor 20 and the second magnetic field coil L2 draws the circuit and connects it to the ground through a loop connected in series by a capacitor C3 and the resistor R3, and simultaneously draws a circuit from the junction of the capacitor C3 and the resistor R3 to A Gate (Gate) of a Field Effect Transistor 30 whose Source is grounded to control the action of the Field Effect Transistor 30, wherein the Field Effect Transistor may be an N-channel Enhanced Metal Oxide Semiconductor Field Effect Transistor (Enhancement nMOS ), and a signal detection wire 50 is drawn from the drain (Drain) end of the field effect transistor 30 as a signal output, and the power supply of the field effect transistor 30 is provided by an external voltage source Vcc different from the fan power supply Provided via a pull-up resistor (Pull-Up Resistor) R4.

As shown in Figure 2, this is the output waveform diagram of the signal detection wire 50 of the present invention when the fan is in normal operation. The junction of the second magnetic field coil L2 produces a square wave signal whose frequency is proportional to the fan blade speed, and this signal causes the periodic charging and discharging of the RC circuit formed by the capacitor C3 and the resistor R3, so that the signal fed into the field effect transistor 30 It also appears as a periodic waveform with alternating levels of ups and downs. This periodic waveform signal causes the field effect transistor 30 to be turned on intermittently due to the alternation of the level. When the field effect transistor 30 is turned on, the voltage Vcc of its power supply across the pull-up resistor R4 so that the drain presents a low level, and when the field effect transistor 30 is turned off, the level of the drain is the same as the high level of its power supply voltage Vcc, so the signal can be The output of the detection wire 50 obtains a square wave signal whose level range is the same as the power supply voltage applied to the field effect transistor 30 and whose frequency is proportional to the fan blade speed, so the level of the signal depends on the power supply of the field effect transistor The size of the voltage Vcc is not limited by the voltage Vin of the fan power supply as in the conventional technology, so the level of the detected signal can be adjusted by changing the size of the power supply voltage Vcc of the field effect transistor 30, so that the detected signal has Larger range and more diverse applications.

Considering that when the fan fails, the output waveform of the signal detection wire 50 can be as shown in Figure 3. When the fan is not running, according to the difference in the stop position of the fan blade rotor, the original position of the second transistor 20 and the second magnetic field coil The square wave signal at the junction of L2 may be at a high level or a low level. When it is at a low level, the field effect transistor 30 is in a cut-off state and makes the output of the signal detection wire 50 present a high level (as shown in FIG. 3A ), and when it falls at a high level, the DC voltage at the junction cannot be fed into the gate of the field effect transistor 30 due to the blocking of the capacitor C3, so the field effect transistor 30 also enters the cut-off state and makes the signal The output of the detecting wire 50 also presents a high level (as shown in FIG. 3 B ), therefore, when the fan fails and does not operate, the signal detecting wire 50 will always present a specific level (high level), which can be extremely The failure of the fan is clearly detected, which solves the disadvantage of the traditional technology that the level of the output signal cannot be predicted when the fan fails.

In terms of application of the present invention, the rotating speed (RPM) of the fan can be known by the following calculation formula:

RPM=(2f/N)×60, f: frequency, N: number of magnetic poles of the fan;

Because the speed of the fan can be known, it can be known in advance that the speed of the fan is abnormal. The output waveform diagram shown in Figure 4 is the change in the speed of the fan detected by the signal detection wire 50. Make the fan speed change with the temperature, or through the application of other circuits (such as a high-pass rectifier circuit plus a sound or LED warning circuit), so as to issue a warning when the signal detection wire 50 presents a high level and no longer changes.

In addition, the present invention can also provide the detection mode of rotation detection (Rotation Detection), the circuit as shown in Figure 5, it is in Fig. A diode D2 is connected in series between the gates of the transistor 30, and a capacitor C4 is connected to the ground at the junction of the diode D2 and the gate of the field effect transistor 30 to form an application circuit for rotation detection. Its working mode is as follows In the output waveform diagram shown in FIG. 6 , when the fan is running, the output of the signal detection wire 50 is low level, and once the fan stops running, it turns to high level, so it can detect abnormality of the fan with a minimum of components.

To sum up, since the present invention improves the detection circuit of the brushless DC fan, it can not only adjust the detection signal level range and detect fan failure, but also make the detection signal of the fan more convenient and more in line with actual needs; and , can flexibly adjust the size of the external voltage source Vcc according to the needs of practical applications to obtain the required detection signal level range, so that the fan detection signal can be used in a wider range; in addition, it can also clearly detect fan failure and no. Therefore, the detection capability of the DC brushless fan signal is greatly increased.

Claims (3)

1. a DC brushless fan checking circuit comprises the brush DC fan control circuitry that constitutes with hall sensor, two transistor and two field coils, it is characterized in that:

The loop that cross-over connection is connected in series mutually by a capacitor and a resistor between the junction of described transistor seconds and second field coil and earth point, and simultaneously draw the gate of the field-effect transistor that a circuit to powered by the voltage source that is different from fan power supply to control the action of this field effect electric crystal by the junction of this capacitor and resistor, and drain electrode place of this field-effect transistor is drawn a signal and is detected lead certainly, for the situation that detects fan running and detect the fault of fan.

2. DC brushless fan checking circuit according to claim 1 is characterized in that:

Forward be connected in series a diode with the junction of resistor between the gate of field-effect transistor at described capacitor, and be connected one second capacitor with the junction of the gate of field-effect transistor to ground, with the recognition that provides a rotation to detect at this diode.

3. DC brushless fan checking circuit according to claim 1 and 2 is characterized in that:

Described field-effect transistor is that a N channel enhancement metal oxide semiconductor field effect is answered transistor.

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