JP3414889B2 - Fan control circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a fan control circuit for controlling the rotation speed of a fan motor which constitutes an air conditioning system for automobiles.

[0002]

2. Description of the Related Art As a fan control circuit for controlling the rotation speed of a fan motor, for example, as shown in FIG.
There is a type field effect transistor 10 (hereinafter, referred to as MOSFET) that controls the applied voltage of the fan motor 12 steplessly. In this circuit, CP
The voltage applied to the fan motor 12 is controlled by mainly amplifying the control signal from U14 by the operational amplifier 16 in the subsequent stage to change the gate voltage of the MOSFET 10. The voltage applied to the fan motor 12 is a voltage between two points A and B that sandwich the fan motor 12 (voltage between terminals), that is, the voltage of the accessory power supply (ACC) that is the power supply of the fan motor 12 and the output of the drain of the MOSFET 10. It is given as the difference from the voltage.

The operational amplifier 18 in the preceding stage constitutes a voltage follower circuit so that the output thereof is not affected by any load connected to the output terminal. Of the two input terminals of the operational amplifier 16 in the subsequent stage, the output of the operational amplifier 18 in the previous stage is given to the non-inverting input terminal (+),
The voltage of the accessory power supply (ACC) which is the power supply of the fan motor 12 is divided and applied to the inverting input terminal (-) by the resistors R2 and R4. The gain of the operational amplifier 16 is determined by the resistors R1, R2, R3, and R4. For example, the gain of the voltage follower circuit (operational amplifier 18) at the front stage is set to 1 and the gain of the operational amplifier 16 at the rear stage is set to 6, respectively. And the overall amplification gain is 1 × 6 = 6
Has doubled.

Further, conventionally, a capacitor C1 having one end grounded is connected to the inverting input terminal (-) of the operational amplifier 16. The capacitor C1 is for releasing high-frequency noise that enters the circuit point E and may be input to the inverting input terminal (-) of the operational amplifier 16 to the ground. On the other hand, the high frequency noise that has entered the non-inverting input terminal (+) of the operational amplifier 16 is dropped to the ground via the capacitor C2 and the capacitor C1. High-frequency noise is mixed in the circuit due to various causes such as radio waves.

[0005]

However, in the conventional fan control circuit configured as described above, the inverting input terminal (-) of the operational amplifier 16 is connected to the capacitor C1 for removing high frequency noise. Therefore, if low-frequency ripple noise is mixed in from the accessory power supply of the fan motor 12 to the point E of the circuit, the ripple noise is smoothed by the capacitor C1 and the resistor R4, and the output of the operational amplifier 16 is smoothed, so that the output of the fan motor 12 is smoothed. The voltage at the point B applied to one terminal (the drain output of the MOSFET 10) is also smoothed. At this time, the fan motor 12
Since the voltage at the point A (voltage of the accessory power supply) given to the other terminal of the device contains ripple noise, after all,
The voltage applied to the fan motor 12 (= voltage at point A−voltage at point B) includes a low-frequency AC component (noise).
When the voltage applied to the fan motor 12 fluctuates due to noise in this manner, the fan motor 12 vibrates, and this vibration is amplified by the resin case that houses the fan motor 12, which may cause abnormal noise. Note that the low-frequency ripple noise is an AC noise characteristic that appears in the DC output from the power supply unit when, for example, the capacity of the alternator that constitutes the power supply unit and the capacity of the battery are not matched.

As a measure for preventing the generation of abnormal noise due to low frequency ripple noise, conventionally, for example, a member for covering the resin case for housing the fan motor 12 is further provided to suppress the vibration of the resin case, Alternatively, the power supply itself has a function of suppressing the occurrence of ripples. However, if such measures are taken, an increase in cost is inevitable.

The present invention has been made in view of the above problems of the prior art. It is possible to remove the influence of high frequency noise and effectively generate abnormal noise due to ripple noise without increasing the cost. An object of the present invention is to provide a fan control circuit which can be prevented.

[0008]

[Means for Solving the Problems]

In order to achieve the above object, the invention according to claim 1 controls a voltage applied to a fan motor while changing a gate voltage of a MOS field effect transistor by an output of an operational amplifier at a final stage. In, while applying the power supply voltage of the fan motor divided by a resistor to one input terminal of the operational amplifier,
A signal removing circuit for removing the output of the operational amplifier when the fan motor is not operating is connected to the output terminal of the operational amplifier, and a noise removing capacitor is not connected to the input terminal of the operational amplifier. Characterize.

According to a second aspect of the invention, the operational amplifier of the preceding stage is provided.
Output a control signal from the final stage operational amplifier to the MOS by the control signal amplified by the final stage operational amplifier.
In a fan control circuit for controlling an applied voltage of a fan motor while changing a gate voltage of a field effect transistor, a power supply voltage of the fan motor is divided by a resistor and applied to one input terminal of the final stage operational amplifier. together, to have a gain in the previous stage of the operational amplifier, and connect the signal removal circuit for removing the output of the operational amplifier of the final stage at the time of non-operation of the fan motor to the output terminal of the operational amplifier of the last stage Therefore, a noise removing capacitor is not connected to the input terminal of the final stage operational amplifier.

[0011]

[Action]

[0012] In the invention of the thus configured according to claim 1, the operational amplifier in the final stage, the input terminal on the side where the power supply is connected to the fan motor is connected to a capacitor for noise removal Therefore, when low frequency ripple noise is mixed into the circuit from the power source, the ripple noise appears in the output of the operational amplifier as it is without being smoothed. Therefore, since the ripple noise of the same phase is given to both terminals of the fan motor, the AC characteristics of the applied voltage of the fan motor becomes 0V by subtracting them, and as a result, no abnormal noise is generated. On the other hand, since the signal removing circuit removes the output of the operational amplifier when the fan motor is not operating, the high frequency noise that enters the circuit when the fan motor is not operating is output to the fan motor even if it is amplified by the operational amplifier. There is no risk of malfunction. Thus, the prevention of malfunction due to high frequency noise and the prevention of abnormal noise due to ripple noise can be achieved only by improving the circuit.

According to the second aspect of the present invention, since the noise eliminating capacitor is not connected to the input terminal of the final stage operational amplifier to the side to which the power source of the fan motor is connected, the circuit has the above structure. When low-frequency ripple noise is mixed from the power supply, the ripple noise appears in the output of the final stage operational amplifier as it is without being smoothed. Therefore, since the ripple noise of the same phase is given to both terminals of the fan motor, the AC characteristics of the applied voltage of the fan motor becomes 0V by subtracting them, and as a result, no abnormal noise is generated. On the other hand, if the gain is
By the way, since the final stage operational amplifier has a small gain, even if high frequency noise enters the circuit during the control of the fan motor, the noise is not amplified so much,
The influence on the output can be suppressed to a small level. Further, since the signal removing circuit removes the output of the operational amplifier when the fan motor is not operating, the high frequency noise that has entered the circuit when the fan motor is not operating is output to the fan motor even if it is amplified by the operational amplifier. There is no risk of malfunction. Thus, only by improving the circuit, the influence of high frequency noise is always removed regardless of whether the fan motor is operating or not, and at the same time, the generation of abnormal noise due to ripple noise is prevented.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a fan control circuit according to an embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals. The circuit shown in FIG. 1 has almost the same basic configuration as the conventional circuit shown in FIG. 2, but in order to prevent the generation of abnormal noise due to ripple noise while maintaining the high frequency noise removal function, the circuit shown in FIG. On the other hand, the following three improvements have been added. That is, first, as a countermeasure against abnormal noise due to ripple noise, the capacitor C1 for removing high frequency noise provided in the conventional circuit is deleted, and secondly, in connection with the removal of the capacitor C1, high frequency noise removal is performed. As a countermeasure, the operational amplifier 18 in the previous stage is provided with a gain and the gain of the operational amplifier 16 in the subsequent stage is lowered. Thirdly, as a countermeasure against high frequency noise, a transistor circuit as a signal removing circuit is provided at the output of the operational amplifier 16 in the subsequent stage. 20 are added. In this circuit,
Since the two operational amplifiers 16 and 18 are used, the operational amplifier 16 in the subsequent stage becomes the operational amplifier in the final stage.

In the following, the configuration of the circuit of this embodiment will be described first, taking these differences into consideration. A microcomputer (CPU) is an auto-amplifier that controls each part of an automobile air conditioner.
14 built-in, output port P20 of this CPU 14
A transistor circuit 22 is connected to. CPU1
A control signal (rectangular pulse signal) for the fan motor 12 is output from the output port P20 of No. 4. The transistor circuit 22 functions to amplify the control current output from the output port P20 and secure the current. Transistor circuit 2
Resistor R is connected to the collector of transistor TR1
A power source Vcc (for example, 5 V) is connected via 5. The transistor circuit 22 may be omitted depending on the function of the CPU 14.

A smoothing circuit composed of a resistor R6 and a capacitor C3 is connected to the transistor circuit 22. The capacitor C3 is composed of an electrolytic capacitor. The smoothing circuit has a function of smoothing a rectangular wave signal output from the CPU 14. The control signal smoothed by the smoothing circuit is applied to the non-inverting input terminal (+) of the operational amplifier 18 in the preceding stage.

The operational amplifier 18 has its output terminal connected to the inverting input terminal (-) via the resistor Rf, and receives the input signal (control signal) from the non-inverting input terminal (+). At this time, the output voltage is applied to the inverting input terminal (-) by two resistors Rf.
Since the voltage divided by Rs and Rs is applied, the operational amplifier 1
A gain of 8 will be given by (1 + Rf / Rs). In the present embodiment, the gain of the operational amplifier 16 in the subsequent stage is lowered, so that the gain which was 1 in the conventional circuit is set to 3, for example. Resistors Rf and Rs have large resistance values (for example, 10
Therefore, the operational amplifier 18 has a function of transmitting a stable and stable output to a subsequent circuit without mutual interference. Operational amplifier 1
The output terminal of 8 is connected to the operational amplifier 16 of the latter stage through the resistor R1.
Is connected to the non-inverting input terminal (+).

A transistor circuit 24 is connected between the resistor R1 and the non-inverting input terminal (+) of the operational amplifier 16. Specifically, the collector of the transistor TR2 constituting the transistor circuit 24 is connected between the resistor R1 and the non-inverting input terminal (+) of the operational amplifier 16,
The emitter is grounded. Also, the transistor TR
The base of 2 is an output port P22 of the CPU 14 via a resistor.
It is connected to the. The transistor circuit 24 has a function of performing signal processing for turning off the fan motor 12, and when a signal (for example, 5V) is output from the output port P22 of the CPU 14, the transistor TR is turned on.
2 is turned on, the output of the operational amplifier 18 (control signal from the CPU 14) is dropped to the ground, and the fan motor 12
Not output to. On the other hand, when the output signal from the output port P22 of the CPU 14 disappears, the transistor TR2 is turned off, so that the output of the operational amplifier 18 is transmitted to the non-inverting input terminal (+) of the operational amplifier 16 in the subsequent stage. .

Non-inverting input terminal (+) of the operational amplifier 16
Is the operational amplifier 1 of the preceding stage via the resistor R1 as described above.
8 is connected to the output terminal of the fan motor 12 and one terminal of the fan motor 12 and the MOSFET 10 via the resistor R3.
Connected to point B between the drains of the. Since the drain voltage of the MOSFET 10 that reflects the output of the operational amplifier 16 is applied to the point B, the output of the operational amplifier 16 is eventually fed back to the non-inverting input terminal (+). On the other hand, the inverting input terminal (-) of the operational amplifier 16 is connected to the point A between the other terminal of the fan motor 12 and the accessory power supply (ACC) via the resistor R2, and is connected to the inverting input terminal (-). Is the voltage of the accessory power supply (ACC), which is the power supply of the fan motor 12, and the two resistances R2 and R4.
The voltage divided by is given. Therefore, the gain of the operational amplifier 16 in the subsequent stage is four resistors R1, R2, R3,
Determined by R4. For example, when the resistance values are set so that R1 = R4 and R3 = R2 are satisfied, the gain of the operational amplifier 16 is R3 / R1 (or R2 / R4).
) Is given. In the present embodiment, the gain which was 6 in the conventional circuit is lowered to 2, for example. In this case, the total amplification gain of the operational amplifiers 18 and 16 in the front stage and the rear stage is 3 × 2 = 6 times.
X6 = 6 times). As described above, in this embodiment, the capacitor C1 connected to the inverting input terminal (-) of the operational amplifier 16 in parallel with the resistor R4 in the conventional circuit is deleted.

A capacitor C2 is connected between the non-inverting input terminal (+) and the inverting input terminal (-) of the operational amplifier 16. This capacitor C2 is for removing the high frequency noise that has entered the non-inverting input terminal (+) of the operational amplifier 16, and has the function of setting the AC component between the two inputs of the operational amplifier 16 to 0V. . A resistor C3 forming a feedback circuit is connected in parallel with a capacitor C4 for phase correction. Further, a capacitor C5 is connected to the power supply line of the operational amplifier 16, and this capacitor C5 is for grounding high frequency noise that has entered the power supply line of the operational amplifier 16.
Although the resistor R7 is a load resistor, it may be omitted because the fan motor 12 that is a load exists.

A capacitor C6 and a resistor R8 are connected between the output terminal of the operational amplifier 16 and the ground. The capacitor C6 removes noise and removes the operational amplifier 16
Of the operational amplifier 16 is converted into a voltage by the resistor R8. The voltage converted by the resistor R8 is MO as the gate voltage.
It is applied to the gate of SFET 10. The resistor R9 is for current protection and for attenuating current energy.

The auto-amplifier including the CPU 14, the operational amplifiers 18 and 16 and the like are connected to the external MOSFET 10 and the fan motor 12 by connectors 26, 28 and 30. Specifically, two points A and B sandwiching both terminals of the fan motor 12 are respectively connected to the connector 26,
The resistor R2 (that is, the inverting input terminal (-) of the operational amplifier 16) and the resistor R3 (that is, the non-inverting input terminal (+) of the operational amplifier 16) are connected via 28. The gate of the MOSFET 10 is connected to the resistor R9 (that is, the output terminal of the operational amplifier 16) via the connector 30.

In this embodiment, a transistor circuit 20 as a signal removing circuit is connected between the resistor R9 and the connector 30. Specifically, this transistor circuit 20
The collector of the transistor TR3 constituting the transistor is connected between the resistor R9 and the connector 30, and the emitter is grounded. Further, the base of the transistor TR3 is connected to the output port P22 of the CPU 14 via the resistor, like the transistor circuit 24. This transistor circuit 20
Has a function of preventing malfunction of the fan motor 12 when the fan motor 12 is in an off state. That is, when a signal is output from the output port P22 of the CPU 14, the transistor circuit 24 operates to stop the fan motor 12 as described above, but at the same time, in the transistor circuit 20, the transistor TR3 also turns on. , The output of the operational amplifier 16 is dropped to the ground and is not output to the fan motor 12. That is, for example, even if high frequency noise enters the inverting input terminal (-) of the operational amplifier 16 and is amplified by the operational amplifier 16 and output, the transistor circuit 20 surely drops it to the ground. A malfunction will be prevented. The transistor TR2 of the transistor circuit 24 is the operational amplifier 18
If the output of the transistor can be 0V, the transistor circuit 20
It can be deleted by adding the transistor TR3.

Capacitors C7 and C8 are connected to the connectors 26 and 28, respectively, in order to allow noise mainly entering from the outside to escape to the ground.

Next, the operation of the circuit configured as described above will be described. When the target temperature is set, the CPU 14
In the case of automatic control, it is based on the input signals from various sensors not shown (for example, inside air sensor, outside air sensor, solar radiation sensor, etc.), and in the case of manual selection, it is based on the signal from the selected air volume switch. A target air volume is determined by performing arithmetic processing, and a control signal (rectangular pulse signal) corresponding to the determined target value for air volume control is output from the output port P20. At this time, the output from the output port P22 is low.
Therefore, the transistor circuits 24 and 20 are both off.

The control signal output from the port P20 of the CPU 14 is smoothed by the smoothing circuit (the resistor R6 and the capacitor C3) after the current is secured by the transistor circuit 22, and the gain of 3 is provided in the preceding operational amplifier 18. Is amplified three times by the non-inverting input terminal (+) of the operational amplifier 16 in the subsequent stage.
Be transmitted to.

The operational amplifier 16 in the subsequent stage has resistors R1 and R2.
, R3, R4 determines the gain (here,
2), which further amplifies the input control signal by a factor of 2 and outputs it. The output (current) of the operational amplifier 16 is a resistor R
It is converted into a voltage by 8 and this voltage is given to the gate of the MOSFET 10 as a gate voltage. MOSFET
Reference numeral 10 gives a drain voltage corresponding to the gate voltage to one terminal (point B) of the fan motor 12. At this time, since the voltage of the accessory power supply (ACC) is applied to the other terminal (point A) of the fan motor 12, the applied voltage of the fan motor 12 is the voltage of the accessory power supply (ACC) (point A). It is a value obtained by subtracting the drain voltage (voltage at the point B) of the MOSFET 10 from (voltage). That is, the voltage applied to the fan motor 12 is steplessly controlled by the gate voltage according to the control signal output from the CPU 14. The fan motor 12 has its applied voltage (more specifically,
It rotates at a rotation speed according to its DC component). At that time, M
The drain voltage (voltage at point B) of the OSFET 10 is fed back to the non-inverting input terminal (+) of the operational amplifier 16, and the gate voltage is automatically adjusted so that the voltage actually applied to the fan motor 12 matches the target value. Controlled by.

Accessory power supply (ACC) during the above operation
Therefore, if low frequency ripple noise is mixed into the line (point E) of the inverting input terminal (-) of the operational amplifier 16, there is no capacitor C1 (see FIG. 2) used in the conventional circuit. It appears in the output of the operational amplifier 16, that is, the gate voltage of the MOSFET 10 without being smoothed, and the noise component of the drain voltage (voltage at the point B) of the MOSFET 10 has the same phase as the ripple noise at the point A. Therefore, the AC component of the voltage applied to the fan motor 12 becomes 0 V, and as a result, the fan motor 12
Since the vibration of is eliminated, no abnormal noise is generated by the ripple noise.

Further, even if high frequency noise is mixed in at point E during operation of the fan motor 12, the gain of the operational amplifier 16 is low, specifically, it is set to twice the conventional one-third. The mixed high frequency noise is not amplified so much by the operational amplifier 16, and its influence is minimized.

On the other hand, when the fan motor 12 is stopped, the CPU 14 outputs a 5V signal from the output port P22. As a result, both the transistor circuits 24 and 20 are turned on. The transistor circuit 24 in the ON state drops the output of the operational amplifier 18 in the previous stage to the ground, and blocks the transmission of the output to the subsequent stage circuit. Also,
By turning on the transistor circuit 20, even if high-frequency noise is mixed in at the point E, the output of the operational amplifier 16 is dropped to the ground due to the noise, so that it is effective that the fan motor 12 malfunctions due to the noise. To be prevented.

Therefore, according to the present embodiment, the capacitor C1 used in the conventional circuit is deleted, and the ripple noise mixed at the point E from the accessory power supply (ACC) is directly input to the operational amplifier 16 and the drain of the MOSFET 10 is inputted. Since the voltage is output to the point B, the AC characteristic of the applied voltage of the fan motor 12 becomes 0 V, and the generation of abnormal noise due to ripple noise can be effectively prevented.

Further, since the operational amplifier 18 in the previous stage is provided with a gain and the gain of the operational amplifier 16 in the subsequent stage is lowered, it is mixed into the point E during the operation of the fan motor 12 while maintaining the overall amplification gain. It is possible to minimize the influence of output due to high frequency noise. Further, the transistor circuit 20 is added to the output terminal of the operational amplifier 16 in the subsequent stage so as to prevent the output of the operational amplifier 16 from being transmitted to the fan motor 12 when the fan motor 12 is not operating. The malfunction of the fan motor 12 due to the high frequency noise mixed in at the point E during the stop is prevented. Therefore, regardless of whether the fan motor 12 is operating or not, the influence of the high frequency noise mixed in the point E can be always removed, and the deleted capacitor C can be removed.
It is possible to realize a high-frequency noise removal function similar to the function of 1.

Therefore, according to the present embodiment, it is possible to effectively prevent generation of abnormal noise due to low-frequency ripple noise while maintaining the resistance to high-frequency noise and in a manner compatible with it.

Moreover, in the present embodiment, as a measure against abnormal noise due to ripple noise, it is not necessary to double-cover the fan motor 12 or add a function of suppressing the occurrence of ripples to the power source itself as in the conventional case. Since it can be dealt with only by changing the cost, there is almost no increase in cost, which is extremely advantageous in terms of cost.

In the present embodiment, as a countermeasure against high frequency noise, the gain of the operational amplifier 16 in the subsequent stage is lowered and the transistor circuit 20 is provided so as to cope with both the operation and non-operation of the fan motor 12. We have taken two additional measures, but in some cases it is possible to adopt only one of them.

[0036]

【The invention's effect】

[0037] As described above, according to the first aspect of the invention, together with providing a Ripurunoizu the same phase to both terminals of the fan motor without using a capacitor for noise removal, the output terminal of the operational amplifier in the final stage Since the signal removing circuit is added to the above, it is possible to effectively prevent generation of abnormal noise due to ripple noise while preventing malfunction due to high frequency noise while the fan motor is stopped. Moreover, since only the circuit is improved, there is almost no increase in cost.

According to the second aspect of the present invention, the ripple noise of the same phase is applied to both terminals of the fan motor without using the noise removing capacitor, and the calculation increase in the preceding stage is performed.
Since the width of the operational amplifier is given a gain and the gain of the final stage operational amplifier is reduced, and the signal elimination circuit is added to the output terminal of the operational amplifier, the influence of high frequency noise during the operation of the fan motor is minimized. It is possible to effectively prevent the generation of abnormal noise due to ripple noise while suppressing the malfunction of the fan motor due to high-frequency noise while the fan motor is stopped. Moreover, since only the circuit is improved, there is almost no increase in cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a fan control circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a conventional fan control circuit.

[Explanation of symbols]

10 ... MOS type field effect transistor 12 ... Fan motor 14 ... CPU 16, 18 ... Operational amplifier 20 ... Transistor circuit (signal removal circuit)

Claims (2)

(57) [Claims] 1. A fan control circuit for controlling the applied voltage of a fan motor (12) while changing the gate voltage of a MOS field effect transistor (10) by the output of an operational amplifier (16) at the final stage. (16) The power supply voltage of the fan motor (12) is divided by resistors (R2, R4) and applied to one input terminal of the fan motor (12), and the output terminal of the operational amplifier (16) is supplied with the fan motor (12). A signal removing circuit (2) for removing the output of the operational amplifier (16) when not operating.
0) is connected, and a noise removing capacitor is not connected to the input terminal of the operational amplifier (16). 2. From the operational amplifier (18) in the preceding stage to the final stage
A control signal is output to the operational amplifier (16) , and M is generated by the control signal amplified by the final operational amplifier (16).
A fan control circuit for controlling an applied voltage to a fan motor (12) while changing a gate voltage of an OS type field effect transistor (10), wherein the fan motor (16) is connected to one input terminal of the final stage operational amplifier (16). 12) The power supply voltage of the resistor (R2, R
4) It is divided and given according to 4), and the operation of the preceding stage is performed.
The gain is given to the amplifier (18) , and the fan motor (1) is connected to the output terminal of the final stage operational amplifier (16).
A signal removing circuit (20) for removing the output of the final stage operational amplifier (16) when not operating in 2) is connected, and the input terminal of the final stage operational amplifier (16) is used for noise removal. Fan control circuit characterized by not connecting the capacitor of.