JP2009281774A - Current sensor - Google Patents

Abstract

An object of the present invention is to provide a current sensor capable of dynamically removing an offset and having high responsiveness.
A current sensor includes: a first current sensor that detects and outputs a current flowing through an output conductor; a first storage unit that stores an output signal of the first current sensor as first digital data; A first section detecting unit 33 that detects a first section in which the first digital data is less than or equal to a predetermined value, and a second trimming method that detects and outputs a current flowing in the output conductor 2 to remove a predetermined offset amount. The offset amount is calculated based on the current sensor 20, the second storage unit 42 that stores the output signal of the second current sensor 20 as second digital data, and the second digital data in the second section corresponding to the first section. The offset calculating part 43 and the offset setting part 44 which sets this offset amount as predetermined | prescribed offset amount are provided.
[Selection] Figure 1

Description

  The present invention relates to a current sensor using a Hall element.

Conventionally, current values of line currents of various electric devices are detected using a current sensor using a Hall element.
In this current sensor, specifically, a core having a gap is prepared and arranged so that the line current to be measured passes on the central axis of the core. A Hall element is disposed between the gaps, and a control current is passed through the Hall element.
According to this current sensor, the magnetic force generated in proportion to the line current is converged by the core and passes through the Hall element. Then, this Hall element converts the magnetic force into a voltage and outputs it as a detection signal.

By the way, the Hall element constituting the above current sensor has a unique offset voltage due to component difference, individual difference, and the like.
Therefore, a method for removing the offset of the current sensor by a trimming method or a chopper method has been proposed.
The trimming method is a method of measuring the offset voltage of the Hall element in advance and removing the offset voltage based on the measurement result (see, for example, Patent Document 1).
JP 2005-300303 A

  However, although this trimming method has high responsiveness, it is necessary to measure the offset voltage in advance, and the offset voltage has a characteristic that it changes with the change of the ambient temperature or the passage of time. In some cases, the level of the offset voltage changed.

On the other hand, the chopper method is a method of removing the offset from the detection signal by switching the polarity of the power source supplied to the current sensor at a predetermined frequency and performing a chopping operation of the detection signal.
According to this chopper method, even if the level of the offset voltage changes, the offset voltage can be removed dynamically. However, since the chopping operation is performed, there is a problem that the responsiveness is lowered.

  An object of the present invention is to provide a current sensor that can dynamically remove an offset and has high responsiveness.

  The current sensor of the present invention (for example, a current sensor 1 described later) is a current sensor that measures a current flowing through an output conductor (for example, an output conductor 2 described later) using a Hall element, and a current flowing through the output conductor. A first current sensor (for example, a first current sensor 10 to be described later) and first digital storage means for A / D converting the output signal of the first current sensor and storing it as first digital data (For example, an A / D converter 31 and a first storage unit 32, which will be described later), and first section detection means (for example, a later-described first section) that detects a section of the first digital data that is equal to or less than a predetermined value as the first section. 1 section detector 33) and the polarity of the power source of the Hall element (for example, second Hall element 21 described later) is fixed, the current flowing through the output conductor is detected, and a predetermined offset amount is removed. The output signal of the second current sensor is A / D converted in synchronization with the second trimming current sensor (for example, a second current sensor 20 described later) and the first digital storage means. 2nd digital storage means (for example, A / D converter 41 and 2nd storage part 42 mentioned below) memorize | stored as 2 digital data, and the part equivalent to the said 1st area is made into a 2nd area about the said 2nd digital data An offset calculating means (for example, an offset calculating section 43 described later) that extracts and calculates an offset amount based on the digital data of the second section, and an offset amount calculated by the offset calculating means is used as the predetermined offset amount. Offset setting means for setting (for example, an offset setting unit 44 described later).

According to the present invention, when the first digital data output from the first current sensor is equal to or less than a predetermined value, a section that is equal to or less than the predetermined value is determined as a section in which no current flows through the output conductor, To detect.
Then, a second section corresponding to the first section is extracted from the second digital data output from the second current sensor. Since the second section is a section in which no current flows through the output conductor, it can be determined that the data value of the second section is substantially equal to the offset amount of the second current sensor. From the output of.

Therefore, the offset amount can be updated each time a state in which no current flows through the output conductor, so that the offset can be removed dynamically without interrupting the measurement of the current value.
Further, since the second current sensor is a trimming type current sensor with high responsiveness, responsiveness can be secured by removing the offset from the output of the second current sensor.

  In this case, when the first section detection means detects the first section, the storage processing by the first digital storage means and the second digital storage means is interrupted, and the offset calculation means and the offset setting means are driven, It is preferable that the storage process is resumed after the setting of the predetermined offset amount by the offset setting means is completed.

  According to the present invention, since the storage process by the first digital storage means and the second digital storage means is interrupted from the detection of the first section until the setting of the predetermined offset amount is completed, the adjustment of the offset amount is performed. Can be performed smoothly.

  In this case, the first current sensor includes a Hall element (for example, a first Hall element 11 described later), and the polarity of the power source of the Hall element is switched to perform a chopping operation of the detection signal. It is preferable to output the detection signal after removing the offset.

  According to the present invention, since the first current sensor is a chopper-type current sensor, the offset can be reliably removed from the detection signal, and the first section in which no current flows through the output conductor can be reliably detected.

  In this case, it is preferable that the second section corresponding to the first section is earlier than the first section by a predetermined phase.

  When a chopper type current sensor is used as the first current sensor, a response time is delayed with respect to the trimming type second current sensor. However, according to the present invention, since the second section corresponding to the first section is made faster than the first section by a predetermined phase, a delay in response time of the first current sensor to the second current sensor can be eliminated.

  In this case, it is preferable that the first current sensor is a shunt resistor connected in series to the output conductor.

  According to this invention, since the first current sensor is a shunt resistor, the manufacturing cost of the current sensor can be reduced.

  According to the present invention, the offset amount can be updated each time a state where no current flows in the output conductor, so that the offset can be removed dynamically without interrupting the measurement of the current value. Further, since the second current sensor is a trimming type current sensor with high responsiveness, responsiveness can be secured by removing the offset from the output of the second current sensor.

Hereinafter, an embodiment of the present invention will be described.
FIG. 1 is a diagram showing a configuration of a current sensor 1 according to an embodiment of the present invention.
The current sensor 1 includes a first current sensor 10, an A / D converter 31 serving as a first digital storage unit, a first storage unit 32 serving as a first digital storage unit, and a first section detection unit 33 serving as a first section detection unit. , Second current sensor 20, A / D converter 41 as second digital storage means, second storage section 42 as second digital storage means, offset calculation section 43 as offset calculation means, and offset setting means An offset setting unit 44 is provided.

The first current sensor 10 detects and outputs a current flowing through the output conductor 2.
FIG. 2 is a diagram illustrating the configuration of the signal processing circuit of the first current sensor 10.
The first current sensor 10 includes a first Hall element 11, a switch network 12, and a differential amplifier 13, and is a chopper-type current sensor capable of switching the polarity of the power source of the first Hall element 11 at a predetermined frequency. is there.

  The differential amplifier 13 amplifies and outputs a difference between two input signals. Here, it is assumed that the gain of the differential amplifier 13 is set to an appropriate value.

  The first Hall element 11 is a substantially cross-shaped element that converts magnetism into an electric signal, and is relative to the direction in which the Hall terminals 11a and 11b provided opposite to each other and the arrangement direction of these 11a and 11b intersect. Hall terminals 11c and 11d provided in the direction.

  The switch network 12 includes four changeover switches Sa, Sb, Sc, and Sd. The switch Sa connects the hall terminal 11 a to the constant current source 14 or the positive terminal of the differential amplifier 13. The switch Sb connects the hall terminal 11 b to the ground or the negative terminal of the differential amplifier 13. The switch Sc connects the hall terminal 11 c to the constant current source 14 or the positive terminal of the differential amplifier 13. The switch Sd connects the hall terminal 11 d to the ground or the negative terminal of the differential amplifier 13.

  In the switch network 12, the switches Sa, Sd, Sb, and Sc are controlled to connect the hall terminal 11 a to the constant current source 14, connect the hall terminal 11 b to the ground, and connect the hall terminal 11 c to the positive amplifier 13. Connected to the terminal, the Hall terminal 11d connected to the negative terminal of the differential amplifier 13, the Hall terminal 11a connected to the positive terminal of the differential amplifier 13, and the Hall terminal 11b connected to the negative terminal of the differential amplifier 13. The Hall terminal 11c is connected to the constant current source 14, and the Hall terminal 11d is connected to the ground.

  According to the first current sensor 10 described above, the polarity of the output signal can be reversed by switching the polarity of the current supplied from the constant current source 14 to the first Hall element 11 by controlling the switch network 12.

  The second current sensor 20 detects the current flowing through the output conductor 2, removes a predetermined offset amount by the offset variable unit 25, and outputs it.

FIG. 3 is a diagram illustrating a configuration of a signal processing circuit of the second current sensor 20.
The second current sensor 20 includes a second Hall element 21 and a differential amplifier 22, and is a trimming type current sensor in which the polarity of the power source of the second Hall element 21 is fixed.

  The differential amplifier 22 amplifies and outputs a difference between two input signals. Here, it is assumed that the gain of the differential amplifier 22 is set to an appropriate value.

The second Hall element 21 is a substantially cross-shaped element that converts magnetism into an electrical signal, and is relative to the direction in which the Hall terminals 21a and 21b provided opposite to each other and the arrangement direction of these 21a and 21b intersect. Hall terminals 21c and 21d provided in the direction.
The hall terminal 21 a is connected to the constant current source 23, the hall terminal 21 b is connected to the ground, the hall terminal 21 c is connected to the positive terminal of the differential amplifier 22, and the hall terminal 21 d is the negative terminal of the differential amplifier 22. Connected to the terminal.

The offset variable unit 25 is a D / A converter, which converts the output signal from the offset setting unit 44 into an analog signal and outputs the analog signal to the negative terminal of the differential amplifier 22, thereby detecting the detection signal of the second Hall element 21. A predetermined offset amount is removed.
In the present embodiment, the offset variable unit 25 is a D / A converter, but is not limited thereto, and may be a potentiometer.

The first storage unit 32 stores the signal output from the first current sensor 10 and A / D converted by the A / D converter 31 as first digital data over a certain period.
The first storage unit 32 is a memory having an FIFO structure, and stores data at times t0 to t (n−1), for example, as shown in FIG.

The 1st area detection part 33 detects the area below a predetermined value among 1st digital data as a 1st area.
Here, the fixed period is a time required to calculate the offset amount, and the predetermined value is, for example, zero.
Specifically, as shown in FIG. 5, a moving average filter based on the four first digital data is used to remove noise. That is, the average value calculation means 331 calculates an average value of the four first digital data as a moving average value. Then, the comparison means 332 compares the obtained moving average value with a predetermined value, and when the moving average value is continuously equal to or less than the predetermined value over a certain period, this section is output as the first section. To do.

The 2nd memory | storage part 42 memorize | stores the signal output from the 2nd current sensor 20, and A / D-converted by the A / D converter 41 as 2nd digital data over a fixed period.
The second storage unit 42 has the same configuration as the first storage unit 32.

  When the first section is detected by the first section detector 33, the offset calculator 43 extracts a portion corresponding to the first section as the second section from the second digital data stored in the second storage section 42. Then, the offset amount is calculated based on the second digital data in the second section. Specifically, the offset amount is calculated so that the data value of the second section becomes zero.

Here, the chopper type first current sensor 10 uses a low-pass filter in order to suppress chopping noise. Although the high-frequency component of the signal can be removed by this low-pass filter, a phase delay occurs in the signal. On the other hand, the trimming-type second current sensor 20 does not use a low-pass filter, and therefore hardly causes a signal phase delay.
Therefore, the first current sensor 10 of the chopper method has a slower response time than the second current sensor 20 of the trimming method. Therefore, when extracting the second section, the delay time of the response time is taken into consideration. There is a need.

Specifically, as shown in FIG. 6, in order to remove noise, a moving average filter based on the four second digital data is used. That is, the average value calculation means 431 calculates the average value of the four second digital data as the moving average value.
Here, considering the response time delay of the first current sensor 10, the second storage unit 42 uses the moving average value (see FIG. 5) obtained using the data at times t 3 to t 6 in the first storage unit 32. On the other hand, the moving average value obtained using the data at times t4 to t7 corresponds.

  The offset setting unit 44 sets the offset amount calculated by the offset calculation unit 43 as a predetermined offset amount of the offset variable unit 25.

The operation of the current sensor 1 will be described with reference to the flowchart of FIG.
In step S <b> 1, the first current sensor 10 detects the current flowing through the output conductor 2.
In step S2, the A / D converter 31 A / D converts the output signal of the first current sensor 10 to generate first digital data.
In step S <b> 3, the first storage unit 32 stores the generated first digital data.

In step S <b> 4, the second current sensor 20 detects the current flowing through the output conductor 2.
In step S5, the A / D converter 41 A / D converts the output signal of the second current sensor 20 to generate second digital data.
In step S6, the second storage unit 42 stores the generated second digital data.

  In step S7, the first section detection unit 33 detects the first section based on the first digital data. Specifically, as shown in FIG. 8A, a section that is equal to or smaller than a predetermined value a among the data values of the first digital data is detected as the first section. This predetermined value a is zero or a value close to zero.

  In step S8, the offset calculation unit 43 determines whether the first section is detected. If this determination is YES, the storage processing of the first storage unit 32 and the second storage unit 42 is temporarily interrupted, and the process proceeds to step S9. If NO, the process returns to step S1.

In step S9, the second digital data is read by the offset calculation unit 43, and in step S10, the offset amount is calculated.
Specifically, as shown in FIG. 8B, a portion corresponding to the first interval is extracted as the second interval for the second digital data. The phase of the second section is earlier than that of the first section.
The first section is a section in which the data value is equal to or less than the predetermined value a, that is, the current of the output conductor 2 is substantially zero. Therefore, the data value in the second section can be handled as the offset amount f of the second current sensor 20.

  In step S <b> 11, the offset setting unit 44 sets the offset amount f calculated by the offset calculation unit 43 as a predetermined offset amount of the offset variable unit 25. After setting the offset amount, the storage processing of the first storage unit 32 and the second storage unit 42 is resumed, and the process returns to step S1.

According to this embodiment, there are the following effects.
(1) Since the offset amount can be updated each time a state in which no current flows in the output conductor 2, the offset can be removed dynamically without interrupting the measurement of the current value.
Further, since the second current sensor 20 is a trimming type current sensor with high responsiveness, responsiveness can be secured by removing the offset from the output of the second current sensor 20.

  (2) Since the storage process by the first storage unit 32 and the second storage unit 42 is interrupted until the setting of the predetermined offset amount f is completed after the first section is detected, the offset amount f is adjusted. It can be done smoothly.

  (3) Since the first current sensor 10 is a chopper-type current sensor, the offset can be reliably removed from the detection signal, and the first section in which no current flows through the output conductor 2 can be reliably detected.

  (4) Since the second section corresponding to the first section is made faster than the first section by a predetermined phase, a delay in response time of the first current sensor 10 to the second current sensor 20 can be eliminated.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the present embodiment, the first current sensor 10 is a chopper-type current sensor. However, the present invention is not limited thereto, and the first current sensor may be a shunt resistor connected in series to the output conductor 2. In this way, the manufacturing cost of the current sensor 1 can be reduced.

It is a figure which shows the structure of the current sensor which concerns on one Embodiment of this invention. It is a figure which shows the structure of the signal processing circuit of the 1st current sensor of the current sensor which concerns on the said embodiment. It is a figure which shows the structure of the signal processing circuit of the 2nd current sensor of the current sensor which concerns on the said embodiment. It is a figure for demonstrating operation | movement of the 1st digital memory | storage means of the current sensor which concerns on the said embodiment. It is a figure for demonstrating operation | movement of the 1st area detection means of the current sensor which concerns on the said embodiment. It is a figure for demonstrating operation | movement of the offset calculating means of the current sensor which concerns on the said embodiment. It is a flowchart which shows operation | movement of the current sensor which concerns on the said embodiment. It is a figure for demonstrating operation | movement of the current sensor which concerns on the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current sensor 2 Output lead 10 1st current sensor 11 1st Hall element 20 2nd current sensor 21 2nd Hall element 31 A / D converter (1st digital memory means)
32 1st memory | storage part (1st digital memory means)
33 1st section detection part (1st section detection means)
41 A / D converter (second digital storage means)
42 2nd memory | storage part (2nd digital memory means)
43 Offset calculator (offset calculator)
44 Offset setting unit (offset setting means)

Claims (5)

A current sensor that measures the current flowing through the output conductor using a Hall element,
A first current sensor for detecting and outputting a current flowing through the output conductor;
First digital storage means for A / D converting the output signal of the first current sensor and storing it as first digital data;
First section detecting means for detecting a section of the first digital data that is equal to or less than a predetermined value as a first section;
A trimming-type second current sensor that fixes the polarity of the power supply of the Hall element, detects a current flowing through the output conductor, removes a predetermined offset amount, and outputs it;
Second digital storage means for A / D converting and storing the output signal of the second current sensor as second digital data in synchronization with the first digital storage means;
About the second digital data, an offset calculating means for extracting a portion corresponding to the first section as a second section and calculating an offset amount based on the digital data of the second section;
A current sensor comprising: an offset setting unit configured to set an offset amount calculated by the offset calculation unit as the predetermined offset amount. The current sensor according to claim 1.
When the first section detection means detects the first section, the storage processing by the first digital storage means and the second digital storage means is interrupted, the offset calculation means and the offset setting means are driven, and the offset setting is performed. The storage process is resumed after the setting of the predetermined offset amount by the means is completed. The current sensor according to claim 1 or 2,
The first current sensor includes a Hall element,
A current sensor characterized in that the polarity of the power source of the hall element is switched and the detection signal is chopped to remove the offset from the detection signal and output the detected signal. The current sensor according to claim 3.
The current sensor, wherein the second section corresponding to the first section is earlier than the first section by a predetermined phase. The current sensor according to claim 1 or 2,
The first current sensor is a shunt resistor connected in series to an output conductor.

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