JP2008164449A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an accurate current measurement result by minimizing the influence of the noise received by the current measurement information by converting an analog voltage value at which the current to be measured is detected into pulse width information and digitally transmitting it. <P>SOLUTION: This current sensor comprises a detection resistor 1 where current to be measured flows, a comparator 4 where the detection voltage occurring at both ends or voltage proportional to the detection voltage is applied to one input end and a triangle wave or sawtooth wave having linear gradient is applied to the other input end, and a magnetic coupler 5 for electrically insulating and transmitting a PWM output signal of the comparator 4 whose pulse width is varied by the detection voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a “current sensor for current value measurement” used for machine tools, hybrid cars, EV cars (electric cars), etc., and in particular, “detection resistance through which current to be measured flows” and “processing of measurement results”. The present invention relates to a current sensor in which a “circuit portion” is electrically insulated by a “magnetic coupler”.

As a method of measuring the current value, a detection resistor is inserted into the circuit through which the current to be measured flows, the voltage at both ends thereof is measured, and the current to be measured is measured by Ohm's law from the known resistance value of the detection resistor. Generally,
(1) For example, in a factory where the noise environment is very bad (eg, a line where a robot assembles a car), the resistance value of the detection resistor is 100 μΩ, the measured current is 200 A, and the voltage at both ends is 20 mV. Since only a voltage is generated and only a signal of several mV is generated with a small current, noise is also mixed into the “measurement result processing circuit section” due to the influence of external noise, and the S / N ratio is deteriorated. Therefore, it is necessary to electrically insulate the measured current side from the “measurement result processing circuit unit” to eliminate the influence of noise as much as possible to reduce the measurement error.
(2) For example, in hybrid cars and EV cars, a large amount of electric power is required to drive the motor. Therefore, the operating voltage of a nickel metal hydride battery or a lithium ion battery is reduced to HV ( High-Voltage: High voltage of about 200V to 400V is used, but the ECU side (consisting of a microprocessor, AD converter and other logic ICs) is a 5V LV (Low-Voltage). Therefore, the HV block and the LV block must be insulated from each other for the purpose of preventing damage to parts and preventing electric shock.

  As shown in the above examples (1) and (2), there is a need for a current sensor having a structure in which the “detection resistor through which the current to be measured flows” and the “processing circuit section of the measurement result” are electrically insulated. .

  As a prior art, there is an “electric quantity detection sensor” disclosed in Patent Document 1 below.

In JP-A-2002-196020, in this Patent Document 1, the primary block to be insulated is constituted by a detection resistor and a series circuit of a phototransistor and a transformer primary winding connected between both ends, The secondary side light-emitting diodes are intermittently blinked by the output of the oscillation circuit, the primary side phototransistor is turned on / off, and the voltage generated in the primary side detection resistor is applied to the transformer secondary side winding. Electromagnetic induction is performed, and output is obtained by synchronous detection based on the output of the oscillation circuit.

The following points can be cited as problems of Patent Document 1.
(1) The measured current value, that is, the analog voltage generated at both ends of the detection resistor is transmitted via a transformer (insulation means), and the amplitude of the minute voltage including noise generated only by the turns ratio is used as the analog value. As a result of transmission, the S / N ratio deteriorates and the measurement error increases.
(2) Since a phototransistor is used as the intermittent means, the response is about 10 μs, the intermittent frequency is only raised to several hundred kHz, and the response is slow.

  Specifically, for example, in order to reduce the power loss to 2 W, the current to be measured is 200 A, the resistance value of the detection resistor is 100 μΩ, and the generated voltage is 20 mV (at 200 A full scale). Therefore, for example, when the current to be measured is 50 A, the generated voltage becomes a very small voltage of 5 mV, and the analog voltage value is transmitted in a state where the S / N ratio due to noise is bad.

  In view of the above points, the present invention converts the analog voltage value detected from the current to be measured into pulse width information and transmits it digitally, thereby minimizing the influence of noise on the current measurement information and achieving high accuracy. It is an object of the present invention to provide a current sensor that can obtain the current measurement result.

  In addition, the present invention uses a high-speed response magnetic coupler to electrically insulate the high-voltage side and the low-voltage side, and transmits the analog voltage value detected from the current under measurement as pulse width information via the magnetic coupler. Thus, another object is to provide a current sensor that can obtain a current measurement result with good responsiveness.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

  In order to achieve the above object, a current sensor according to an aspect of the present invention has a detection resistor through which a current to be measured flows, a detection voltage generated at both ends thereof, or a voltage directly proportional to the detection voltage applied to one input terminal. And a first PWM output signal of a first comparator in which a triangular wave or a sawtooth wave having a linear slope is applied to the other input terminal, and a first comparator whose pulse width varies depending on the detection voltage, And a magnetic coupler for electrically insulating and transmitting.

  The current sensor may further include a second comparator in which an output signal of the magnetic coupler is applied to one input terminal, and a reference voltage is applied to the other input terminal. The two comparators can output a logic level second PWM output signal.

  In the current sensor, the second PWM output signal may be input to a microprocessor, and the microprocessor may calculate a duty ratio of the second PWM output signal to obtain a sensor output.

  In the current sensor, the second PWM output signal may be converted into an average value to obtain a sensor output.

  In the current sensor, the magnetic coupler has a transmission coil and a reception coil that are magnetically coupled to each other but are electrically insulated, and supplies the first PWM output signal to the transmission coil. Also good.

  Alternatively, the magnetic coupler has a structure in which an inductor is provided on one side of an insulator and a magnetic sensitive element is provided on the other side to be electrically insulated from each other, and the first PWM output signal is supplied to the inductor, An AC magnetic field generated by an inductor may be applied to the magnetic sensing element to transmit the pulse width information of the first PWM output signal in a non-contact manner.

  Alternatively, the magnetic coupler has a structure in which a gap is provided in a part of a ferromagnetic core around which a coil is wound, and a magnetically sensitive element is disposed in the gap by being electrically insulated from the core. The first PWM output signal may be supplied, an AC magnetic field generated by the coil may be applied to the magnetic sensitive element, and the pulse width information of the first PWM output signal may be transmitted in a non-contact manner.

  Further, the magnetically sensitive element may be a magnetoresistive element.

  According to the current sensor of the present invention, the measurement information of the current to be measured is not transmitted as an analog voltage value, but is transmitted as pulse width information that does not depend on the signal amplitude, so that the influence of the voltage amplitude change is completely eliminated. The effect of external noise can be reduced as much as possible, and the "synchronous detection circuit" that had to be adopted in the conventional example (Patent Document 1) (in the conventional example, the noise level for a minute value of several mV measurement voltage) Since the S / N ratio is high and the S / N ratio is low, the “oscillation circuit” and the generated voltage are synchronized for detection) can be eliminated. Since the influence of noise on the measurement information of the current to be measured can be reduced as much as possible, the current value measurement result can be made highly accurate even when used in a vehicle having a poor electromagnetic noise environment or in a factory. The measurement error can be improved to about ± 1% in the present invention, compared to the measurement error of about ± 3% in the full scale of the conventional example.

  In addition, in order to electrically insulate the high voltage side from the low voltage side, the response can be improved by using a magnetic coupler instead of using a photocoupler consisting of a pair of light emitting diode and phototransistor. In particular, a magnetoresistive element (here, a concept including a giant magnetoresistive element (hereinafter referred to as GMR element) and a spin valve giant magnetoresistive element (hereinafter referred to as SV-GMR element) as a magnetic sensitive element in the magnetic coupler) By using, the responsiveness can be increased to about several GHz.

  Hereinafter, as the best mode for carrying out the present invention, an embodiment of a current sensor will be described with reference to the drawings.

FIG. 1 shows a first embodiment of a current sensor according to the present invention, in which a detection resistor 1 inserted in a path through which a current to be measured Is flows from a high voltage battery B1 to a load RL, and a detection voltage V generated at both ends thereof. An amplifier 2 that amplifies _A , a triangular wave generator 3 that generates a triangular wave signal, a comparator (comparator) 4 that receives the output voltage V _B of the amplifier 2 and the triangular wave signal, and a PWM (Pulse Width Modulation: pulse) by the comparator 4 (Width modulation) a magnetic coupler 5 that electrically isolates and transmits an output signal, a comparator 6 (waveform shaper) that shapes the output signal of the magnetic coupler 5, and a PWM output signal after waveform shaping, And a processing circuit unit 7 for measuring a measured current value from the PWM output signal. The generation of the PWM output signal by the comparator 4 will be described later.

  Here, the detection resistor 1, the amplifier 2, the triangular wave generator 3, and the comparator 4 are HV blocks, the comparator 6 and the processing circuit unit 7 are LV blocks, and the magnetic coupler 5 electrically insulates them from each other. Thus, the PWM output signal is transmitted. The amplifier 2, the triangular wave generator 3 and the comparator 4 belong to the HV block, but since the operating voltage is low, a low voltage power source electrically isolated from the LV block is prepared. The ground symbol of the HV block and the ground symbol of the LV block are floating (insulated from each other).

The detection resistor 1 is 100 μΩ in this example, and the generated voltage is set to ± 20 mV at the current to be measured Is = ± 200 A full scale. FIG. 2 shows the relationship between the measured current Is and the detection voltage _VA across the detection resistor 1.

The amplifier 2 is a non-inverting amplifier, and includes an operational amplifier OP1 and resistors R1 and R2. One end of the detection resistor 1 is connected to the non-inverting input terminal of the operational amplifier OP1, and the inverting input terminal of the operational amplifier OP1. Is connected to the ground of the HV block together with the other end of the detection resistor 1 via a resistor R2. The detection voltage V _A generated at both ends of the detection resistor 1 and the output voltage V _{B of the} amplifier 2 have a linear relationship. Therefore, the measured current Is and the output voltage V _{B of the} amplifier 2 are as shown in FIG. It is a linear relationship. When the measured current Is = 0A, the output voltage V _B = 0V. When the measured current Is is negative, the output voltage V _B is a negative voltage. When the measured current Is is positive, the output voltage is also a positive voltage. Become. In the case of FIG. 3, the amplification factor of the amplifier 2 is set to 100.

  When the resistance value of the detection resistor 1 is increased, the amplifier 2 can be omitted.

Triangular wave generator 3, FIG. 4 (A1), (A2) , is intended to generate a triangular wave signal V _C shown in (A3), the triangular wave signal, a waveform forming two equilateral isosceles triangle, the straight line A waveform with good characteristics can be generated.

The triangular wave signal V _C from the triangular wave generator 3 is applied to one input terminal of the comparator 4 (non-inverting input terminal), the comparator 4 of the other input terminal (inverting input terminal) to the amplifier 2 of the output signal ( An output voltage V _B ) is supplied.

To explain the operation of the comparator 4 in FIG. 4, when the current to be measured Is = + 200A, higher than the triangular wave signal _{V C} is + 2V in the output voltage _{V B} is + 2V next amplifier 2 from 3, 4 (A1) The output voltage V _D of the comparator 4 is at a high level as shown in FIG. Here, the triangular wave signal is set in advance so that the duty ratio = 10%.

When the measured current Is = 0A, the output voltage _{V B} becomes 0V amplifier 2 from FIG. 3, the output voltage V of the comparator 4 to the extent that the triangular wave signal _{V C} is a voltage higher than 0V in FIG. 4 (A2) _D becomes a high level as shown in FIG. 2B2, and the duty ratio is 50%.

When the measured current Is = -200A, from FIG. 3 the output voltage _{V B} is -2V next amplifier 2, Fig. 4 (A3) triangular wave signal _{V C} is at the comparator 4 to the extent that a voltage higher than -2V the output voltage _{V D} becomes high level, as in FIG. (B3), the duty ratio = 90%.

FIG. 5 shows the relationship between the measured current Is and the duty ratio of the output voltage V _D of the comparator 4. Since the slope of the triangular wave signal V _C is linear, the comparator 4 the first PWM output signal that is pulse width modulated to linearly duty ratio up to the -200A from the measured current Is = + 200A increases Is output.

  FIG. 6 shows an example of the magnetic coupler 5, which includes a transmission coil 11 and a reception coil 12 that are magnetically coupled to each other but are electrically insulated. For example, the transmission coil 11 is fixed to one surface of the insulator sheet (including the substrate) 10, and the reception coil 12 is fixed to the other surface of the insulator sheet 10 so as to be magnetically coupled to the transmission coil 11. The transmission coil 11 and the reception coil 12 may be formed by winding a magnetic core such as ferrite, but may be an air core coil in which the magnetic core is omitted when operating at a high frequency.

  As shown in FIG. 1, the transmitter coil 11 is supplied with the first PWM output signal of the comparator 4, and the voltage induced in the receiver coil 12 is supplied to one input terminal (non-inverting input terminal) of the comparator (comparator) 6. ). The other input terminal (inverted input terminal) of the comparator 6 is connected to the ground of the LV block together with the ground-side terminal of the receiving coil 12.

The comparator 6 functions as a waveform shaper. As an output of the comparator 6, a digital logic level (logic IC input) that repeats a low level (L) and a high level (H) as shown in FIG. A second PWM output signal V _E (having the same pulse width information as the output of the comparator 4) having a pulse width modulated signal level that can be used as a signal as it is is obtained.

Then, when the measured current Is is +200 A, the comparator 6 corresponds to the first PWM output signal V _D having the duty ratio of 10% shown in FIG. 4B1 and the second PWM shown in FIG. the output signal V _E output by the logic level to the processing circuit 7. The duty ratio of the first PWM output signal _{V D} and a second PWM output signal _{V E} is consistent, the duty ratio in this case, the second PWM output signal _{V E} is 10%.

Comparator 6, when the current to be measured Is = 0A, the second PWM output signal in FIG. 7 corresponding to the first PWM output signal _{V D} of the duty ratio of 50% as shown in FIG. 4 (B2) (B) V _E (duty ratio 50%) is output at a logic level.

Comparator 6, when the current to be measured Is = + 200A, a second PWM output signal in FIG. 7 (C) corresponding to the first PWM output signal _{V D} of the duty ratio of 90% as shown in FIG. 4 (B3) V _E (duty ratio 90%) is output at a logic level.

Examples processor section 7 for measuring a current value to be measured from the second PWM output signal V _E, the microprocessor which is commercially available as a so-called one-chip microcomputer can be used. As a one-chip microcomputer, a CPU, a program memory, a data memory, an input / output port, a timer, etc. are integrated in one IC chip, and the second PWM output signal _VE is in one cycle T in FIG. Since it has L / H ratio information (eg, on-duty), it can be read by the timer / counter port of the microprocessor. That is, the period of “low level” and “high level” is counted (counted) for a certain period of time, and the measured current value is finally calculated based on the ratio between “low level” and “high level”. can get. The resolution of the current value to be measured is a function of the clock frequency of the microprocessor and the resolution of the built-in counter.

  According to the first embodiment, the following effects can be obtained.

(1) According to the current sensor according to the present embodiment, the measurement information of the measured current Is is not transmitted as an analog voltage value, but is transmitted digitally as pulse width information independent of the signal amplitude. The influence of external noise can be reduced as much as possible, and the “synchronous detection circuit” that had to be adopted in the conventional example (Patent Document 1) (in the conventional example, the noise level is small for a minute value of several mV). Since the S / N ratio is high and the S / N ratio is low, the “oscillation circuit” and the generated voltage are detected in synchronization with each other).

(2) In order to electrically insulate the high voltage side (HV block) from the low voltage side (LV block), the magnetic coupler 5 should be used without using a photocoupler consisting of a combination of a light emitting diode and a phototransistor. Thus, the response can be improved, and the set of the transmission coil 11 and the reception coil 12 of the magnetic coupler 5 can be sufficiently downsized (or thinned) by setting the use frequency high.

(3) It is less affected by external noise and can improve measurement accuracy. For example, the measurement error in the full scale of the conventional example is about ± 3%, and in this embodiment, it can be improved to about ± 1%.

(4) In the case of in-vehicle use, since the magnetic coupler 5, the comparator 6 and the processing circuit unit 7 are housed in the ECU, the wiring connecting the comparator 4 and the magnetic coupler 5 on the high voltage side (HV block) is long. However, the output of the comparator 4 is a PWM output and is not affected by fluctuations in the voltage amplitude, and therefore is not easily affected by external noise.

(5) as a processing circuit section 7 can use a microprocessor which is commercially available as a 1-chip microcomputer, by inputting a second PWM output signal V _E to the timer counter port, a second PWM output signal V _E The current value to be measured can be measured based on the ratio of “low level” to “high level”, and a pulse width modulated waveform can be read with a simple circuit configuration, and high-speed response is possible.

FIG. 8 shows a second embodiment of the present invention. In this case, the configuration of the magnetic coupler and the comparator at the subsequent stage are different. The magnetic coupler 15 includes a transmission coil 11 that is magnetically coupled to each other but electrically insulated, and an SV-GMR element 16 as a magnetically sensitive element. The transmission coil 11 is a chip inductor 20 in which a winding 22 is wound around a ferromagnetic drum core 21 such as ferrite as shown in FIG. 9, for example, and is provided and fixed on one surface of an insulator sheet (including a substrate) 23. The SV-GMR element 16 is provided and fixed on the other surface of the insulator sheet 23, and is electrically insulated from each other by the insulator sheet 23. Then, the first PWM output signal V _D of the comparator 4 is supplied to the winding 22, and the AC magnetic field generated by the chip inductor 20 (the magnetic field changes in accordance with the pulse width of the first PWM output signal). It is applied so as to penetrate the SV-GMR element 16, and pulse width information is transmitted in a non-contact manner.

  In terms of operation principle, the magnetic sensitive element used for the magnetic coupler 15 may be any element that can extract the amount of magnetic change as a change in the amount of electricity. Among the elements, GMR elements, particularly SV-GMR elements are preferable.

  The SV-GMR element includes a magnetic pinned layer whose magnetization direction is fixed in one direction, and a ferromagnetic free layer stacked on the pinned layer via a nonmagnetic material through which a current mainly flows. The pinned layer has a resistance effect film, the magnetization direction of the pinned layer is not changed by the external magnetic field (external magnetic flux), and the magnetization direction of the free layer is changed to the direction of the external magnetic field (external magnetic flux). Here, when the magnetization direction of the pinned layer and the magnetization direction of the free layer (that is, the direction of the external magnetic field) in the magnetoresistive effect film are parallel but opposite in direction, that is, antiparallel, the rate of change in resistance becomes positive. It becomes a high resistance state. When the magnetization direction of the pinned layer and the magnetization direction of the free layer (that is, the direction of the external magnetic field) are parallel and in the same direction, that is, in the forward parallel direction, the resistance change rate becomes negative and a low resistance state is obtained.

  In this example, the first PWM output signal of the comparator 4 is arranged so that a magnetic flux caused by flowing in the winding 22 of the chip inductor 20 is applied in parallel to the pinned layer magnetization direction of the SV-GMR element 16. preferable.

As shown in FIG. 8, the DC bias circuit of the SV-GMR element 16 in the magnetic coupler 15 connects the SV-GMR element 16 and the series resistor R3 to a DC power source Vcc having a constant voltage (for example, DC 5V). A bias is given. Then, SV-GMR from a connection point between the elements 16 and the series resistor R3, periodic change in resistance of SV-GMR element 16 a voltage signal _{V F} of Figure 10 in accordance with the (corresponding to the change of the magnetic flux) of the comparator 6 Is output. As shown in FIG. 10, the voltage signal V _F is (having the same pulse width information and the output of the comparator 4) AC waveform around the DC bias is superposed.

Comparator 6 having a waveform shaping function, the reference voltage Vref (eg: 2.5V) to its inverting input is applied to the non-inverting input voltage signal V _F of the magnetic coupler 15 is supplied. Reference voltage Vref is set to the maximum value and intermediate value of the minimum value of the voltage signal V _F of FIG. 10 (a value substantially equal to the DC bias), thereby, the logic level of FIG. 7 as the output of the comparator 6 A pulse width modulated second PWM output signal V _E (having the same pulse width information as the output of the comparator 4) is obtained.

  The other circuit configuration of the second embodiment is the same as that of the first embodiment in FIG. 1, and the same or corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  According to the second embodiment, without using a phototransistor, a magnetic coupler 15 using a high-speed responsive magnetoresistive element (specifically, SV-GMR element 16) as a magnetic sensitive element is used. High-speed response is possible, and the speed can be increased to about several GHz. In addition, the SV-GMR element 16 is ultra-compact, and can be further reduced in size compared to the case where a set of a transmission coil and a reception coil is used.

FIGS. 11A and 11B show another example of the magnetic coupler 15 that can be used in the second embodiment. The magnetic core 31 is made of a ferromagnetic material (permalloy or the like) around which at least one spiral coil 30 is wound. A gap G is provided in a part of the structure, and an SV-GMR element 16 as a magnetically sensitive element is arranged in the gap G by being electrically insulated from the core 31. Thus, by applying an AC magnetic field in which the magnetic field coincides with the pulse width of the first PWM output signal V _D of the comparator 4 is changed to SV-GMR element 16, it transmits the pulse width information in a non-contact. The spiral coil 30 and the core 31 may be non-insulated.

12A and 12B show another example of the magnetic coupler 15 that can be used in the second embodiment. The core 41 of a ferromagnetic body (permalloy or the like) around which at least one solenoid coil 40 is wound. A gap G is provided in a part, and the SV-GMR element 16 as a magnetically sensitive element is disposed in the gap G by being electrically insulated from the core 41. Again applying an AC magnetic field in which the magnetic field coincides with the pulse width of the first PWM output signal V _D of the comparator 4 is changed to SV-GMR element 16, capable of transmitting the pulse width information in a non-contact.

In the first and second embodiments, the case where a microprocessor is used as the processing circuit unit 7 has been described. However, the averaging circuit 50 shown in FIG. Averaging circuit 50 is an integral circuit composed of a resistor R4 and the capacitor C1, can be a second PWM output signal V _E are averaged to obtain a sensor output Vout of the DC.

  FIG. 14 shows an example of the input / output characteristics when the averaging circuit 50 is used, and shows the relationship between the measured current Is and the sensor output Vout. When the measured current Is = + 200 A, the sensor output Vout = 0.5 V, when the measured current Is = 0 A, the sensor output Vout = 2.5 V, and when the measured current Is = −200 A, the sensor output Vout = 4.5 V.

FIG. 15 shows a pulse width modulation operation when a sawtooth wave generator (not shown) is used instead of the triangular wave generator of the first and second embodiments. Sawtooth generator, FIG. 15 (A1), (A2) , is intended to generate a sawtooth signal V _G shown in (A3), the sawtooth wave signal, slope linear, linear monotonically increasing period The waveform is good.

Sawtooth signal V _G is one input terminal of the comparator 4 in the first and second embodiments of the sawtooth generator is applied to (the non-inverting input terminal), the other input of the comparator 4 (inverting input terminal) Is supplied with the output signal (output voltage V _B ) of the amplifier 2.

To explain the operation of the comparator 4 in FIG. 15, when the current to be measured Is = + 200A, the output voltage _{V B} is + 2V next amplifier 2 from 3, than the sawtooth signal _{V G} is + 2V in FIG. 15 (A1) The output voltage V _D of the comparator 4 is at a high level as shown in FIG. Here, the sawtooth signal is set in advance so that the duty ratio = 10%.

When the measured current Is = 0A, the output voltage of the amplifier 2 from FIG. 3 _{V B} becomes 0V, 15 sawtooth signal _{V G} is the output voltage of the comparator 4 to the extent that a voltage higher than 0V in (A2) V _D becomes high level, as in FIG. (B2), the duty ratio = 50%.

When the measured current Is = −200 A, the output voltage V _B of the amplifier 2 is −2 V from FIG. 3, and the comparator 4 is within a range where the sawtooth wave signal V _G in FIG. 15 (A 3) is higher than −2 V. Output voltage V _D becomes high level as shown in FIG. 5B3, and the duty ratio becomes 90%.

  Other operations are the same as those in the first and second embodiments.

In the first and second embodiments described above, a configuration may be adopted in which a triangular wave or a sawtooth wave is applied to the inverting input terminal of the comparator 4 and the output voltage V _B of the amplifier 2 is supplied to the non-inverting input terminal. In this case, the measured current Is-duty ratio characteristic is reversed (the duty ratio increases linearly as the measured current Is increases).

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS It is Embodiment 1 of the current sensor which concerns on this invention, and is a block diagram of the whole structure. It is a graph which shows the relationship between the to-be-measured current Is in embodiment, and the detection voltage _{VA of} both ends of a detection resistor. Is a graph showing the relationship between the output voltage V _B of the measured current Is and the amplifier. An output voltage V _B of the triangular wave signal and amplifier, a waveform diagram showing the relationship between the first PWM output signal which is the output of the first comparator. It is a graph which shows the relationship between to-be-measured current Is and the duty ratio of a 1st PWM output signal. 2 is a front sectional view showing an example of a magnetic coupler in Embodiment 1. FIG. It is a wave form diagram of the 2nd PWM output signal which is an output of the 2nd comparator by the side of LV block. It is Embodiment 2 of the current sensor which concerns on this invention, and is a block diagram of the whole structure. 6 is a front sectional view showing an example of a magnetic coupler in Embodiment 2. FIG. It is a waveform diagram of the output voltage signal V _F of the magnetic coupler. It is another example of a magnetic coupler, (A) is a perspective view, (B) is a plane sectional view. It is another example of a magnetic coupler, (A) is a front view, (B) is a top view. 6 is a circuit diagram illustrating another example of a processing circuit unit that can be used in the first and second embodiments. FIG. 14 is an output characteristic diagram showing a relationship between a measured current Is and a sensor output voltage Vout when the processing circuit unit of FIG. 13 is used. It is a wave form chart for operation explanation at the time of using a sawtooth wave instead of a triangular wave.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Detection resistor 2 Amplifier 3 Triangular wave generator 4,6 Comparator 5,15 Magnetic coupler 7 Processing circuit part 10 Insulator sheet 11 Transmitting coil 12 Receiving coil 16 SV-GMR element 20 Chip inductor 30 Spiral coil 31, 41 Core 40 Solenoid coil 50 Averaging circuit C1 Capacitor G Gap OP1 Operational amplifier R1-R4 Resistance Vref Reference voltage

Claims (8)

A sensing resistor through which the current under measurement flows,
A first comparator in which a detection voltage generated at both ends thereof or a voltage directly proportional to the detection voltage is applied to one input terminal, and a triangular wave or a sawtooth wave having a linear slope is applied to the other input terminal;
A current sensor, comprising: a magnetic coupler that electrically insulates and transmits a first PWM output signal of a first comparator whose pulse width varies depending on the detection voltage.   The magnetic circuit further includes a second comparator in which an output signal of the magnetic coupler is applied to one input terminal and a reference voltage is applied to the other input terminal, and the second comparator has a logic level second PWM. The current sensor according to claim 1, wherein an output signal is output.   3. The current sensor according to claim 2, wherein the second PWM output signal is input to a microprocessor, and the microprocessor calculates a duty ratio of the second PWM output signal to obtain a sensor output.   The current sensor according to claim 2, wherein the second PWM output signal is converted into an average value to obtain a sensor output.   The magnetic coupler includes a transmission coil and a reception coil that are magnetically coupled to each other but are electrically isolated, and supplies the first PWM output signal to the transmission coil. The current sensor according to 1, 2, 3, or 4.   The magnetic coupler has a structure in which an inductor is provided on one side of an insulator and a magnetic sensing element is provided on the other side to be electrically insulated from each other, and the first PWM output signal is supplied to the inductor. 5. The current sensor according to claim 1, wherein the generated AC magnetic field is applied to the magnetosensitive element to transmit the pulse width information of the first PWM output signal in a non-contact manner.   The magnetic coupler has a structure in which a gap is provided in a part of a ferromagnetic core around which a coil is wound, and a magnetically sensitive element is disposed in the gap by being electrically insulated from the core. The PWM output signal of 1 is supplied, the alternating current magnetic field by the said coil is applied to the said magnetic sensitive element, The pulse width information of the said 1st PWM output signal is transmitted non-contactingly, It is characterized by the above-mentioned. , 3 or 4 current sensor.   8. The current sensor according to claim 6, wherein the magnetic sensitive element is a magnetoresistive element.

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