JPH087243B2 - Digital current detector - Google Patents

Description

The present invention relates to a current detection device, and more particularly to a digital output current detection device.

[Conventional technology]

Conventionally, an analog output device as shown in FIG. 4 is known as a current detection device.

This device detects the magnetic field Hi created by the detected current by the Hall element 40, amplifies it by the amplifier 41, takes it out as the analog output Oa through the current booster 42, and also causes the current to flow through the secondary coil 43 to generate the magnetic field of the detected current. There is a feedback type current detector that operates so as to give feedback so as to cancel Hi.

However, recently, since many devices using the current detector are digital control devices, the current detection device is also required to have a digital output. Therefore, the analog output obtained by this device is expensively analog-to-digital converted to obtain a digital output.

[Problems to be Solved by the Invention]

The above-mentioned conventional device requires an expensive analog / digital converter to obtain a digital output, and since the current detection device is analog, it is vulnerable to disturbance and has many adjustment points.

The present invention has been made in view of the above points, and an object thereof is to use an expensive analog / digital converter, and
An object of the present invention is to provide a digital current detection device capable of obtaining a highly accurate digital amount by compensating for disturbance, offset, and drift, which have been problems in analog circuits.

[Means for solving the problem]

In order to achieve the above object, the present invention configures a digital current detection device as follows. The reference numerals of the constituent elements are those of the embodiment shown in FIG.

That is, the feedback secondary coil 7 is added to the magnetic field Hi generated by the current to be detected in the direction of canceling the feedback magnetic field Hf, and the magnetic detection for magnetic field detection is performed in the feedback loop for generating the feedback magnetic field Hf. Element 1
An amplifier 2 that amplifies the output of the magnetic detection element 1, a voltage comparator 3 that compares the output voltage Ez of the amplifier 2 with a predetermined reference voltage Er, and an output voltage Ez of the voltage comparator 3.
Is higher than the reference voltage Er, the reference clock is counted up (down), and if it is lower than the reference voltage Er, the up / down counter 4 that counts down (up) and the digital output of the up / down counter 4 are converted into analog signals.
The converter 5 and the current booster 6 that supplies the analog output of the D / A converter 5 to the feedback secondary coil 7 as a current for generating the feedback magnetic field Hf are connected, and the digital output Od of the up / down counter 4 is connected. The feedback type current detection system and the tracking comparison type A / D converter are constructed in the same feedback loop by taking out as the current detection signal.

[Action]

According to the above configuration, when the magnetic detection element 1 detects the magnetic field Hi created by the detected current, the amplifier of the feedback loop
2, voltage comparator 3, up / down counter 4, D / A converter 5, current booster 6, secondary coil 7 for feedback
Feedback field Hf in the direction to cancel the magnetic field Hi via
Occurs in the magnetic circuit (corresponding to the magnetic body 1A in FIG. 2). The output of the amplifier 2 in the latter stage of the magnetic detection element 1 at this time serves as the basis of the feedback magnetic field Hf output, but it is assumed that it corresponds to the magnetic field Hi and thus the current to be detected, and it is digitalized via the voltage comparator 3 and the up / down counter 4. It can be taken out as a value. When the detected current changes, a difference ΔH between the magnetic fields Hi and Hf occurs, but in this case as well, Hf feedback commensurate with the magnetic field ΔH is applied by the feedback loop, and this is digitally output via the up / down counter 4. It

For example, if Hf is fed back so that ΔH becomes zero, the reference voltage Er of the voltage comparator is set to zero. In this case, the input voltage Ez of the comparator 3 is set.
When Ez <0 due to a change in ΔH, the up / down counter 4 counts down (or counts up) more than the current state, and when Ez> 0, counts up (or counts down). In this way, the comparator 3 and the up / down counter 4 become a follow-up comparison type A / D converter, and the detected current is detected from the digital output.

As described above, since the analog circuit element of the feedback type current detection system and the tracking comparison type A / D converter are configured in the same feedback loop, disturbance, offset and drift are also compensated. For example, when the offset voltage is superimposed on the output of the amplifier 2, the offset voltage eO is added to the voltage Ez corresponding to the original detected current i, and the secondary coil 7 receives the detected current i as the feedback current ic. A considerable amount of current and a small amount of current iO flowing to eO flow (ic =
i + iO, and in order to pass iO, the amplification factor of the amplifier 2 may be increased).
After the voltage of iO is converted by the magnetic detection element 1, it is negatively fed back to the amplifier 2 so that the offset voltage eO is canceled out and the offset voltage is compensated. This is similarly compensated for the drift and disturbance of the analog signal transmission system, and the up / down counter 4 (the digital signal Od corresponding to the detected current i is supplied from the feedback loop system in which such compensation is performed. Since it can be taken out via a comparison type current detector), the current detection accuracy is improved.

〔Example〕

 An embodiment of the present invention will be described with reference to FIGS.

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

In FIG. 1, Hi is a magnetic field generated by the detected current. With respect to this magnetic field Hi, the feedback secondary coil 7 creates a feedback magnetic field Hf in the direction of canceling Hi through the feedback type current detection system described below.

In the feedback loop for generating the feedback magnetic field Hf, the Hall element (magnetic detection element) 1
Amplifier 2, zero cross comparator (voltage comparator) 3, up / down counter 4, and D / A converter 5
, Current booster 6 and feedback secondary coil 7
And are connected. The Hall element 1 has a difference ΔH between the magnetic fields Hi and Hf.
Is detected, and an output corresponding to the magnetic field ΔH is generated. This output is amplified by the amplifier 2 and input to the zero cross comparator 3. Zero cross comparator 3 has input voltage Ez
(Amplifier 2 output voltage Ez) is equal to reference voltage Er (here, Er
= 0) to determine whether Ez <0 or Ez> 0. Then, when Ez <0, the output Ec is set to L level, and when Ez> 0, it is set to H level. This output Ec counts up or down the clock CL from the clock oscillator 9 as an up / down switching signal of the up / down counter 4. Digital output Od of this up / down counter 4
After converting to analog value through D / A converter 5,
A current is passed through the secondary coil 7 through the current booth 6 to create a magnetic field Hf generated thereby.

This magnetic field Hf operates so as to exactly cancel the magnetic field Hi created by the detected current i, and feedback is applied so that the added magnetic field ΔH of both is zero. Therefore, the digital output Od that follows the detected current is obtained from the output of the up / down counter 4. In this way, the feedback type current detection system and the tracking comparison type A / D converter (comparator 3, up / down counter 4) are configured in the same feedback loop. Reference numeral 8 is a power supply for driving the Hall element.

FIG. 2 is a specific example of the configuration of the present invention in which the detection mechanism is modeled, and FIG. 3 is a waveform of each part for explaining FIG.

The present invention will be specifically described with reference to FIGS. 2 and 3.
When the current i to be detected is passed through the current terminals I ₁ and I ₂ , a magnetomotive force is generated by the coil C ₁ wound around the magnetic body 1A, and the gap portion of the magnetic body 1A
Magnetic field Hi is generated in GP. The Hall element 1 driven by a constant current i ₀ is arranged in this gap GP. The output e ₀ of the Hall element 1 is amplified by the amplifier 2 and its output is compared with the reference voltage Er by the voltage comparator 3 '. Output e ₀ is reference voltage Er
When it is higher, the output Ec is set to H level, and when it is lower than the reference voltage Er, the output Ec is set to L level. With this voltage Ec, the up / down counter 4 counts up or down the reference clock CL. The output of the counter 4 is a digital quantity, which can be taken out as a digital output Od, and can be further subjected to digital / analog conversion to take out the output as an analog output Oa. Further, it is amplified by the amplifier 10 and the output is resistor R
To the secondary coil 7 wound around the magnetic body 1A, a current is passed through the secondary coil 7 to generate a magnetomotive force in the opposite direction to the magnetomotive force generated by the detected current i, and the detected current i in the air gap GP. Magnetic field created by
It is designed to generate a magnetic field Hf in the opposite direction to Hi, and constitutes a feedback circuit as a whole.

FIG. 3 shows an example of the detected current i having a sine wave as shown. Since the magnetic field Hi proportional to this is generated by the flow of the current i, the output e ₀ of the Hall element 1 also has a waveform as shown by e _{01 in} the case of no feedback. However, since there is feedback, the output e _{0 of the} Hall element 1
Is a substantially constant value as shown by e ₀ . Next, assuming that the reference voltage Er of the voltage comparator 3'is zero, the Hall element 1
If the output e _{0 of} is greater than zero, the voltage comparator 3 '
Output Ec becomes H level, and when it is small, it becomes L level, so H and L are repeated as shown by Ec in the figure. As a result, assuming that the reference clock is CL shown in the figure, the figure shows the magnitude of the digital output Od of the up / down counter CUN4.
It becomes like Od ₁ (pseudo digital quantity). That is, when the voltage Ec is at the H level (a) point, the up / down counter counts up every clock CL and the output increases, and when the voltage Ec is at the L level (b) point, the clock increases.
The output is reduced by counting down for each CL.

When this digital output Od is added to the digital / analog converter 5 and the analog output Oa is filtered, it becomes Oa shown in the figure. This output Oa is connected to the resistor R and 2 through the amplifier 10.
When applied to the next coil 7, the current ic of the coil 7 becomes sinusoidal as shown.

Here, the frequency of the reference clock CL is shown to be about 60 times the frequency of the detected current i. However, if the ratio is increased, the value of the digital output Od becomes a smooth sine wave and the detected current i becomes The response speed to follow up becomes faster.

Further, since the reference voltage Er of the voltage comparator 3'is set to zero in the above embodiment, the magnetic fields Hi and 2 produced by the detected current i are
The next coil 7 operates so that the magnetic field Hf generated by the current ic becomes equal, but when the reference voltage Er has a certain value, it operates so that a predetermined constant difference occurs between the magnetic fields Hi and Hf. By adjusting the reference voltage, a bias magnetic field can be constantly applied to the operating point of the Hall element 1, and the Hall element 1 having excellent sensitivity and linearity can be selected and used. Further, since the analog circuit element of the feedback type current detection system and the tracking comparison type A / D converter are configured in the same feedback loop, disturbance, offset, drift, etc. are compensated. For example, when the offset voltage is superimposed on the output of the amplifier 2, the offset voltage eO is added to the voltage Ez corresponding to the original detected current i, and the secondary coil 7 receives the detected current i as the feedback current ic. A considerable amount of current and a small amount of current iO flowing to eO flow (ic =
i + iO), iO in the feedback current ic is voltage-converted by the magnetic detection element 1 and then negatively fed back to the amplifier 2, so that the offset voltage eO is canceled out and offset voltage compensation is performed. This is similarly compensated for drift and disturbance in the analog signal transmission system, and the up / down counter 4 (the digital signal Od corresponding to the detected current i is supplied from the feedback loop system in which such compensation is performed. Since it can be taken out via a comparison type current detector), the current detection accuracy is improved.

〔The invention's effect〕

As described above, according to the present invention, since the analog circuit element of the feedback type current detection system and the tracking comparison type A / D converter are configured in the same feedback loop, the disturbance and offset generated in the analog signal transmission system The drift can be compensated by a simple circuit configuration, and as a result, the number of adjustment points can be reduced, and a digital current detection device that can obtain a highly accurate digital output can be provided. Further, an expensive and complicated analog / digital converter is not required, and the digital current detection system can be constructed using a simple counter at low cost.

Further, since the operating point of the magnetic field / voltage conversion element can be freely selected, there is an effect that the conversion element having no high characteristics can be sufficiently used.

[Brief description of drawings]

1 to 3 show the configuration of an embodiment of the present invention. FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is another embodiment of the present invention in which a detection mechanism is modeled. FIG. 3 is a configuration diagram showing an embodiment of FIG. 3, FIG. 3 is an operation explanatory diagram of FIG. 2, and FIG. 4 is a configuration diagram of a conventional example. Hi ... magnetic field created by current to be detected, Hf ... magnetic field created by secondary winding, 1 ... Hall element, 1A ... magnetic material, 2 ... amplifier,
3 ... Zero cross comparator, 3 '... Voltage comparator, 4 ... Up / down counter, 5 ... Digital / analog converter, 6 ... Current booster, 7 ... Secondary coil, 8 ... Hall element power, 9 ...... clock generator, 10 ...... amplifier, gap GP ...... magnetic, C ₁ ...... 1 primary coil, CL ...... clock, Er ...... reference voltage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-213783 (JP, A) JP-A 61-225663 (JP, A) JP-A 53-15170 (JP, A) Practical application Sho-57- 168075 (JP, U) Actual development Sho 51-6840 (JP, U) Japanese patent Sho 49-5183 (JP, B1) Japanese public Sho 53-34706 (JP, B2) Japanese public Sho 52-14069 (JP, B2)

Claims (3)

[Claims] 1. A feedback secondary coil for adding a feedback magnetic field Hf to a magnetic field Hi generated by a current to be detected in a direction of canceling the feedback magnetic field Hf, wherein a magnetic field is detected in a feedback loop for generating the feedback magnetic field Hf. A magnetic detection element, an amplifier that amplifies the output of the magnetic detection element, a voltage comparator that compares the output voltage of the amplifier with a predetermined reference voltage, and a reference when the output voltage of the voltage comparator is higher than the reference voltage. An up / down counter that counts up (down) the clock and down (up) when it is low, a D / A converter that converts the digital output of the up / down counter into an analog signal, and the D
An analog output of the A / A converter is connected to the feedback secondary coil as a current booster for supplying the feedback magnetic field Hf as a current, and the digital output of the up / down counter is taken out as a current detection signal. A digital current detection device characterized in that a feedback current detection system and a tracking comparison type A / D converter are configured in the same feedback loop. 2. The digital current detection device according to claim 1, wherein the reference voltage of the voltage comparator is variable. 3. The digital current detector according to claim 1, wherein the digital output is taken out from the output terminal of the up / down counter and the analog output is taken out from the output terminal of the D / A converter. apparatus.