JPH06253573A - Current detecting circuit - Google Patents

Abstract

PURPOSE:To provide a current detecting circuit for detecting a load current having variable magnitude at low cost while suppressing power consumption and fluctuation of power supply voltage. CONSTITUTION:The current detecting circuit comprises a motor 1, a voltage supply E1 for feeding the motor 1 with driving current, a lead wire 4 connected between the motor 1 and the voltage supply E1 and passing a driving current IF, and magnetic inductance elements 5, 6 for detecting the magnitude of the driving current IF flowing through the lead wire 4. The current detecting circuit further comprises a voltage supply E3 connected between one ends of the inductance elements 5, 6, and a multivibrator circuit 9 connected between the other ends of the inductance elements 5, 6 and further connected through the inductance elements 5, 6 with the voltage supply E3 in order to generate signals e1, e2 corresponding to the magnitude of the driving current IF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection circuit, and more particularly to a current detection circuit for detecting a load current whose magnitude varies.

[0002]

2. Description of the Related Art FIG. 9 is a circuit diagram of a motor control circuit to which an example of a conventional current detection circuit is applied.

In FIG. 9, reference numeral 1 denotes, for example, a DC motor for an electric automatic machine, which will be described later from a DC voltage source E ₁ via a coil L ₁ for suppressing an inrush current at the time of starting and a resistor Rx or a resistor Ro. It is driven by being supplied with a direct current as shown in.

There is power between the bottom of both resistors and ground.
The MOS FETs Q ₁ and Q ₂ or Q ₃ and Q ₄ are connected in series as shown, and the DC motor 1 is connected between the common connection points of the power MOS FETs. The rotation direction and speed of the DC motor 1 are determined by the gate G ₁ of each power MOS FET.
Each power MO is controlled by the control signal coming from the control unit 2 to G _4.
It is controlled by switching S FET.

For example, when controlling the direct current motor 1 in the normal direction, the power MOS FETs Q ₁ and Q ₄ are turned off.
And the gates G ₂ and G of the power MOS FETs Q ₂ and Q ₃
A rectangular wave signal having a predetermined timing is supplied to the controller ₃ to turn on both power MOS FETs, and the drive current I _F shown in FIG.
The DC motor 1 is rotated in the normal direction.

Since the drive current I _F varies depending on the mechanical load of the DC motor 1, the control unit 2 controls the control unit 2 to detect the drive current I _F and set it to a predetermined value. Controlling the rotation speed etc. is performed.

The current detection circuit for this purpose is based on the DC amplifier 3
Composed of. The DC amplifier 3 is a differential amplifier operated by a DC power source from the DC voltage source E ₂ , and has a resistance Rx, for example.
The voltage between both ends of is applied to the input terminal. As a result, the DC amplifier 3 supplies the control unit 2 with a voltage according to the magnitude of the drive current I _F flowing through the resistor Rx.

[0008]

However, in order to reduce the power supply of the DC voltage source E ₁ in order to reduce the power consumption, it is necessary to make the resistance Rx low. For example, when the DC motor 1 consumes several tens of amperes, there is a problem in that the resistor Rx for detecting the load current must be a special and expensive one with several tens mΩ.

Further, the DC voltage source E ₂ for supplying the DC power source to the DC amplifier 3 must have a higher voltage than the DC voltage source E ₁ for driving the motor. However, an expensive voltage source that normally generates several tens of volts is required for driving the motor, and in order to reduce the cost, for example, one high-voltage voltage source that is commonly used for driving the motor and driving the amplifier is prepared. The voltage for driving is used by lowering it so that the voltage for driving becomes lower than the voltage for driving an amplifier. Therefore, the power supply voltage supplied to the amplifier may fluctuate due to fluctuations in the magnitude of the load current.

Therefore, it is an object of the present invention to provide a current detection circuit which can be constructed at low cost and low power consumption and in which the power supply voltage supplied to the amplifier does not fluctuate.

[0011]

[Means for Solving the Problems] The above problems can be solved by the following constitution.

That is, a motor, a first power supply for supplying a drive current to the motor, a wiring means connected between the motor and the first power supply to serve as a drive current path, and a wiring means are provided. A current detecting means for detecting the magnitude of the flowing drive current, a second power source connected to one end of the current detecting means,
This is solved by including a signal generating unit that is connected to the other end of the current detecting unit and is connected to the second power source through the current detecting unit, and that generates a signal according to the magnitude of the driving current. .

[0013]

According to the present invention having the above construction, the driving current is supplied from the first power source to the motor through the wiring means. In addition, the signal generation unit operates so as to generate a signal according to the magnitude of the drive current through the current detection unit that is connected to the second power supply that is provided independently of the first power supply.

[0014]

FIG. 1 is a circuit diagram of an embodiment of the present invention. 9, those parts which are the same as those corresponding parts in FIG. 9 are designated by the same reference numerals, and a description thereof will be omitted.

In the figure, the DC voltage source E ₁ is the first
The drive current I _F supplied from the DC voltage source E ₁ to the DC motor 1 is the power source of the coil L ₁ and the power MOS FET Q.
_It flows through a lead wire 4 which is a wiring means for connecting with ₃ . The coil L ₁ is for suppressing inrush current and has a ferrite core material.

The lead wire 4 has an electric resistance R _LEAD and is wound around the magnetic inductance elements 5 and 6 several times. The magnetic inductance elements 5 and 6 and the ferrite magnets 7 and 8 constitute the current detecting means.

For example, as shown in FIG. 2, for example, ferrite magnets 7 and 8 for magnetic bias are arranged so as to face each other so that the magnetic poles have a cylindrical shape in the opposite direction, and the lead wire 4 is wound around this. Then, by inserting the magnetic inductance elements 5 and 6 into the through holes formed in the ferrite magnets 7 and 8, the magnetic inductance elements 5 and 6 are biased by the DC magnetic fields in opposite directions.

[0018] The magnetic inductance element is equivalently represented by a series circuit of a resistor R _M and the inductance L _M as shown in FIG. 3, the inductance L _M according to magnetic flux interlinking
The value of changes.

That is, the magnetic inductance element is shown in FIG.
As shown in, the inductance L _M increases as the magnitude of the magnetic flux φ decreases, and becomes maximum when the magnetic flux φ is zero. Therefore, by detecting the change in the external magnetic field excited by the drive current I _F flowing through the lead wire 4 by the magnetic inductance, the change in the magnitude of the drive current I _F can be detected.

Referring back to FIG. 1, one end of each of the magnetic inductance elements 5 and 6 is a DC voltage source E ₃ which is the second power source, and each other end is a multivibrator circuit 9 which is the signal generating means. It is connected to the. The DC voltage source E ₃ is provided independently of the DC voltage source E _1, and also supplies the power supply current to the DC amplifier 10 that additionally amplifies the output signal from the multivibrator circuit 9.

The magnetic inductance element 5 is the collector load of the transistor Q ₅ which constitutes the multivibrator circuit 9, and the magnetic inductance element 6 is also the collector load of the transistor Q ₆ .

Therefore, when the magnitude of the drive current I _F varies depending on the mechanical load of the DC motor 1 and the magnetic flux linked to the magnetic inductance elements 5 and 6 changes, the inductance value changes as described above. The change causes the voltage drop from E _{3 due} to the magnetic inductance elements 5 and 6 to change.

As a result, the transistor Q_FiveThe emitter of
Resistor R connected between the_FiveSignal at both ends of
Voltage e₁But again, transistor Q_FiveEmitter and graph
Resistor R connected between₆Signal voltage e on both ends of
₂Is generated, and both signal voltages e ₁And e₂Is the drive current I_F
Increases or decreases according to fluctuations in size.

By the way, since the ferrite magnets 7 and 8 are arranged so as to generate opposite bias magnetic fields, the respective peaks of the signal voltages e ₁ and e ₂ have different timings.

Therefore, the value of the balance adjusting half resistance R ₁ connected between the emitters of the transistors Q ₅ and Q ₆ and connected between both input terminals of the DC amplifier 10 is adjusted to adjust the multivibrator circuit 9 , The signal voltages e ₁ and e are applied to the output terminal of the DC amplifier 10.
A signal voltage e _out proportional to the detected magnetic field is obtained by adding and synthesizing the slopes of increase and decrease of ₂ .

The control unit 2 generates the four-phase control signals based on the signal voltage e _out to generate the power MOS FET Q, as described above.
Switching control of _{1 to} Q ₄ controls the rotation direction and speed of the DC motor 1.

According to this embodiment configured as described above,
The power MOS FETs Q _{1 to} Q ₄ are switching-controlled by the controller 2, and the drive current I _F is supplied from the DC voltage source E ₁ to the DC motor 1 through the lead wire 4 wound around the magnetic inductance elements 5 and 6 as a path. To be done. Since the magnetic inductance elements 5 and 6 have extremely high detection sensitivity, the lead wire 4
The drive current I _{F of} about several mA can be detected if the number of windings is set to several tens, and the current consumption can be reduced because a resistor for current detection is not required, which contributes to cost reduction. You can

Further, since the DC voltage source E ₃ is provided independently of the DC voltage source E ₁ for driving the motor, the multivibrator circuit 9, the DC amplifier 10, etc., regardless of the driving conditions of the DC motor 1. The power supply voltage can be set in consideration of operating conditions. Therefore, it is possible to reduce the voltage and power consumption as compared with the conventional case.

When the drive current I _F is a large current of 1 A or more, the number of windings of the lead wire 4 may be small,
For example, it is conceivable to configure the current detecting means as shown in FIG.

Further, when the drive current I _F is a large current, the number of windings of the lead wire 4 may be small. Therefore, it is conceivable to configure the current detecting means as shown in FIG. 5, for example.

In FIG. 5, 17 and 18 are ferrite magnets formed in a U shape and arranged in parallel, 15 and 1.
Reference numeral 6 is a magnetic inductance element arranged so as to form a closed loop with the ferrite magnets 17 and 18, and a lead wire 14 serving as a path of the drive current I _F is arranged so as to be orthogonal to the closed loop magnetic field. With this configuration, a drive current I _{F of} 1 A or more can be detected.

It is also conceivable to omit the above ferrite magnetic field generating ferrite magnets (7, 8, 17, 18). For example, the ferrite core material of the coil L ₁ of FIG. 1 may be magnetized to form a through hole, and a magnetic inductance element for current detection may be inserted.

Alternatively, it is conceivable to omit the ferrite magnet for generating the bias magnetic field by constructing as shown in FIG.

That is, as shown in FIG. 6, the magnetic inductance elements 19 and 20 for current detection connected between the DC voltage source E ₃ and the multivibrator circuit 9 include:
A lead wire 21, which serves as a path for the drive current I _F , is wound. Further, a series circuit including a lead wire 22 and a semi-fixed resistor R ₇ is connected to both ends of the DC voltage source E ₃ .

The lead wire 22 has magnetic inductances so that the magnetic inductance element 19 and the magnetic inductance element 20 are magnetically biased by DC magnetic fields in opposite directions due to the power source current I _C shunted from the DC voltage source E _3. The element is wound in the opposite direction. Therefore, by adjusting the resistance value of the semi-fixed resistor R ₇ , a predetermined bias magnetic field can be applied to each magnetic inductance element without using a ferrite magnet, which is effective for cost reduction.

In each of the above embodiments, the current detection circuit for detecting the drive current of the DC motor has been described, but another embodiment of the present invention in FIG. 7 shows a circuit for detecting the drive current of the AC motor. . In the figure, the same components as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, 31 is an AC motor,
It is driven and controlled by an AC motor control circuit 32 that operates by being supplied with power from a commercial AC power supply e _AC . In addition, the output terminal of the DC amplifier 10 and the AC motor control circuit 3
A series circuit of a rectifying circuit 33 and a buffer 34 is connected between the two.

The input signal waveform and the output signal waveform of the rectifier circuit 33 are as shown in FIG. That is, the signal voltage e _out from the DC amplifier 10 in which the half-wave waveform of the peak value corresponding to the detected current is continuous is input, and the signal voltage e _out ′ smoothed as shown in the figure is output.

This output signal waveform has the same waveform as the signal voltage e _out obtained by the current detection circuit of FIG. 1 with respect to the change of the drive current of the AC motor 31, and in this embodiment, the AC motor control circuit 32 outputs the signal. A control signal is generated based on the voltage e _out ′, and the AC motor 31 is controlled in a predetermined rotation direction and speed.

[0040]

As described above, according to the present invention, since the drive current is supplied from the first power source to the motor through the wiring means as the route, the current consumption can be reduced because the resistor for detecting the current is not required, and the low current consumption can be achieved. In addition to contributing to cost reduction, a signal according to the magnitude of the drive current is generated by the signal generating means via the current detecting means connected to the second power source provided independently of the first power source. Since it is generated, the second power source can be set regardless of the driving condition of the motor, and it has a feature that the voltage can be made lower and power consumption can be made lower than ever before.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a current detection unit in FIG.

FIG. 3 is an equivalent circuit diagram of a magnetic inductance element.

FIG. 4 is a characteristic diagram of a magnetic inductance element.

FIG. 5 is a configuration diagram of another example of a current detection unit.

FIG. 6 is a configuration diagram of still another example of the current detection means.

FIG. 7 is a circuit diagram of another embodiment of the present invention.

FIG. 8 is a signal waveform diagram of a main part of FIG.

FIG. 9 is a circuit diagram of a motor control circuit to which an example of a conventional current detection circuit is applied.

[Explanation of symbols]

1 DC motor 4,14,21 Lead wire 9 Multivibrator circuit 31 AC motor 5,6,15,16,19,20 Magnetic inductance element 22 Lead wire E ₁ , E ₂ , E ₃ DC voltage source e _AC Commercial AC power supply

Claims (2)

[Claims] 1. A motor, a first power supply for supplying a drive current to the motor, and a wiring means connected between the motor and the first power supply to serve as a path for the drive current. Current detecting means for detecting the magnitude of the drive current flowing through the wiring means, a second power source connected to one end of the current detecting means, and current detecting means connected to the other end of the current detecting means A current detecting circuit, which is connected to the second power source via a means, and includes a signal generating means for generating a signal according to the magnitude of the driving current. 2. The current detecting device according to claim 1, further comprising a magnetic inductance element arranged so as to detect an external magnetic field excited by the drive current flowing through the wiring device. Detection circuit.