JPS60173475A - Self-oscillation type current sensor - Google Patents

Abstract

PURPOSE:To decrease the number of parts and to reduce the device in size on the whole by detecting a current through the self-exciting operation of a magnetic semiconductor circuit consisting of a magnetic core with high magnetic permeability and an operational amplifier. CONSTITUTION:When the operational amplifier 9 is saturated positively and a positive voltage Vs developed at a terminal 8, the amplifier 9 keeps on sending a positive saturation voltage Vs to excite the magnetic core 1. The magnetic core 1 decreases in magnetic permeability before magnetic flux density attains to a maximum level and the impedance of winding 3 also decreases; and the voltage at a terminal 3a is inverted into a negative voltage owing to the resonance between a capacitor 6 and the winding 3 and inputted to an uninverted input terminal 10b, so that the voltage at the terminal 8 is switched automatically to a negative DC saturation voltage -Vs. Similarly, the voltage -Vs is changed to +Vs and DC voltages + or -Vc applied to the amplifier 9 develop voltages + or -Vs alternately at the terminal 8 with a voltage signal induced at the winding 3, and the positive/negative period length ratio of the voltage waveforms is controlled with the current to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current sensor that constitutes a magnetic semiconductor coupling circuit using a magnetic core with high magnetic permeability and an operational amplifier, and detects current by the self-excitation operation of this circuit.

A value modulator using an annular magnetic core, which is representative of the conventional current measurement method, is a separately excited type in which an AC excitation power source is provided in a separate circuit. For this reason, the basic configuration includes a magnetic sensing section using an annular magnetic core, a drive circuit section incorporating an AC excitation power source that excites the magnetic core at an excitation frequency f of several KHz to several tens of KHz,
A synchronous rectifier section that amplifies the frequency (2f) of the magnetic core and performs phase detection, and a multiplier circuit section that generates a reference signal of the 2f component from the excitation frequency f and inputs it to the synchronous rectifier section are absolutely necessary. Since it consists of a display circuit section that displays the strength of the current, the circuit configuration is complex and the number of parts is large, making it fundamentally difficult to miniaturize the overall device shape and eliminate parts of each circuit section. Ta. Therefore, it has been particularly difficult to install a current sensor in the limited space of a private residence.

Therefore, the present invention provides a self-oscillation type current sensor which can greatly reduce the number of parts using a very simple circuit system and which can be used even under such environmental conditions. The first feature is that the current is sent from the drive circuit section to the magnetic sensing section - DC transmission, and the magnetic core and operational amplifier itself constitute a magnetic semiconductor coupled self-exciting circuit. The output signal is a square wave AC signal whose ratio of positive and negative half cycle periods is variable depending on the applied magnetic field generated by the input current, and the DC signal obtained by integrating this is used as the target signal for current detection, so that it can be connected to the current sensing section and drive. The circuit part is number 1
A current detection signal can be extracted even from 0 m to several 100 mML D
This is the key to realizing the C-DC transmission system.

The second feature is that magnetic-semiconductor coupling is achieved by using high-permeability materials such as ferrite amorphous materials and permalloy as the magnetic core used in the current sensing part. ・A very stable current-sensitive self-exciting circuit is constructed as a circuit.1- That's another thing. As a result, a high-frequency AC excitation power source and an AC amplitude stabilization circuit are unnecessary.The third characteristic of transmission is that the direction and strength of input current can be determined without using phase detection or amplitude detection circuits. , it has the function of directly converting the output voltage polarity and voltage value, and processing the (m) processing in the current sensing part itself6. The fourth feature (5; ↓, two positive and negative polarities) The current stabilizing power supply causes the current sensing part to miss 1.Ii, and can be shared with the operational amplifier power supply used in the signal processing circuit.
This made common earth possible.

Fifth feature: The d1 current sensing section has extremely low power consumption.
-G is small, so it can coexist on a linear IC level printed circuit board.1. In addition, it can be said that this current sensor method is highly practical and versatile. In other words, the current value that excites the magnetic core is I(
The output of the operational amplifier is sufficient at 1 mA or less, and the second feature is that it can be operated without adding an excitation current amplification circuit using a power transistor.

A detailed explanation will be given below with reference to the drawings.

FIGS. 1(a) to 1(c) show an example of the material structure of a single-hole magnetic core 1 made of a single-hole formable material used in the present invention.

(a) shows an example of an A1 core that has been punched, fired, or etched, (b) shows an example of a magnetic core wound with a tape-shaped magnetic material, and (c) shows an example of a magnetic core wound with a thin ribbon wire or wire. Since the object of the present invention can be achieved with any shape or configuration, there is no particular limitation thereto.

The magnetic core 1 may be a single hole, or its shape is not limited.

The materials used are also not limited to pure iron, silicon steel, permalloy, amorphous, ferrite, etc. Of course, it is also possible to use a thin film obtained by sputtering or the like.

The second recess f/1 shows the basic configuration of the winding wound around the magnetic core of the current sensor in the present invention. Figure 2 (a) Genichi The basic configuration of the present invention is a molded I, D5id single-hole magnetic core with fixed excitation windings and operational amplifier input windings.
On the outside thereof, the excitation winding 2 of the terminals 2a, 21), the operational amplifier input winding 3, and the terminal 4a.

The input winding 4 of the input circuit, which is 4b, is passed through. Input winding 40 The number of turns is J-turn in the figure, or generally -,
Any number of turns may be used as long as the condition of electromagnetically loose coupling is satisfied. Capacitor 6 was added for the purpose of adjusting the switching timing of the operational amplifier and absorbing noise components generated from the magnetic core (/'C1). It was added for the purpose of stabilizing self-excited oscillation. Terminal: 3a.

It is connected to the winding terminal 3b to form a resonant circuit. Figures 2 (b) and (c) show a 12-meter conductor so that a part of the measured current of 1 inch flows into the input winding 4 inside the single hole, and the rest flows through a single or multiple shunt conductor 40 outside the single hole. An example of an input circuit is shown. The special feature of this circuit is that by bypassing the current and measuring only Iex shunted to a predetermined current magnitude, it is possible to measure the large current Iin to be measured with a small magnetic core. In other words, it is possible to measure Iin by converting it from the magnetic field created by the input current Iex passing through this magnetic core.

In such an input circuit configuration, since the alternating current induced from the magnetic core to the input winding is short-circuited by the conductor 40, there is a great advantage that electromagnetic induction to the input circuit is blocked.

FIG. 3 is a diagram for explaining the operating principle of the present invention using the B-Iex characteristics of the magnetic core 5. FIG. 3(a) shows the B-Iex characteristic of the magnetic core 5 when the input current Iex is zero (Iex 20). Since hysteresis exists in the magnetic core 5, the excitation cycle will follow the path of ■→■→(■→(4)→■) as shown in the diagram.Here, ;, 11ex -F), a positive DC voltage is applied to the excitation winding 2 connected to a high resistance, and the positive excitation field moves the magnetic core 5 to a maximum magnetic flux density Bm.
1, the magnetic flux density reaches ΔB]2 while the magnetic flux density is changing, as shown in the figure.

If the DC voltage is made zero at the same time that the magnetic flux density of the magnetic core 5 reaches Bm K, the magnetic field applied to the magnetic core 5 disappears, so the magnetic flux density level quickly returns from point C2) to the level of point (2). Next, when a negative DC voltage is applied and the magnetic core 4 is excited by a negative excitation field to the negative maximum magnetic flux density -Bm, the magnetic flux density becomes ΔB34 during the change, and 1Δ
1ΔB541 holds true for B,2. However, as shown in FIG. 3(b), the positive input current I'ex
Considering the case where the above-mentioned excitation cycle is repeated from the state where the magnetic field generated by 01 is applied to the magnetic core 5, ΔB/1□ during the magnetic flux density change when the positive excitation magnetic field is applied. , ΔB'34 when applying a negative excitation field
Therefore, between ΔB'12 and B'34, 1ΔB'+21 <lΔB'341 holds true. In other words, during the positive excitation period bi+ and the negative excitation period t'- required for the excitation DC voltage to excite the magnetic core 5 from zero to the maximum positive or negative magnetic flux density level, t '
The relational expression 10<t'- holds true.

Next, as shown in FIG. 3(c), the negative input current I″e
When the above excitation cycle is repeated from the state in which the magnetic field generated by During the negative excitation period t''-, t''-t''- is established.Therefore, the excitation DC voltage value applied to the magnetic core 5 during the above-mentioned excitation cycle is at the maximum magnetic flux density level of the magnetic core 5. In order to prevent the current from decreasing or fluctuating, a variable resistor 7 is connected in series with the excitation winding 2, as shown in the current detection circuit of Fig. 4, and the impedance is adjusted by this variable resistor. Considering the case where the polarity of the DC voltage Vc, -Vc is automatically switched at the same time as reaching the maximum magnetic flux density level C2) or (maximum magnetic flux density level C2), the voltage waveform e at the terminal 8 is a square wave voltage waveform having both positive and negative polarities. Figure 5 shows that under these assumptions, Iex = 0, I'ex , > 0, I'ex (
The voltage waveform e at the terminal 8 in each case of 0 is illustrated. As can be seen from the figure, the positive half-cycle duration of the bipolar square wave is 10, t'10t'', and the negative half-cycle duration t-1t+, ttr- is the input current I
It can be seen that it is controlled by ex , I'ex, I″ex. Therefore, by integrating e, its voltage integral value Eo
It can be seen that current measurement can be made possible by converting and displaying the signs and voltage values of % E'o and E''o in correspondence with the polarity and intensity of the current to be measured Iin.

Next, the operating principle of the present invention will be explained with reference to a specific ri]+ path.

FIG. 6 shows an example of a circuit that automatically implements the operating principle of the present invention, and is configured to automatically switch the DC voltage for exciting the magnetic core 5. It consists of a current sensing section 100, a moving circuit section 200 containing a positive/negative drive DC power supply S, and a display circuit section 300 that integrates and amplifies the output of the current sensing section 100.

The explanation about the current sensing part JO() is the inverting terminal of the operational amplifier 9], Oa Id ground G @ ;?
i, non-inverting terminal], Oht/li, terminal 73a of input winding 3 is connected, DiAi terminal: Ubi,
It is earth G. The capacitor 6 is connected to both ends of the winding 3, and absorbs the noise components generated by the magnetic core 5 (so, in terms of circuit construction, it constitutes a resonant circuit for the winding 3, and is used when switching the DC voltage. It contributes to stabilizing the timing operation.The output terminal 8 of the operational amplifier 9 ((
(The variable resistor 7 is connected, and this resistor adjusts the voltage waveform of the output terminal 8. In other words, the load impedance including the variable resistor 7 and the winding 2 is adjusted, so that the output terminal voltage waveform is as rectangular as possible.) Make it into waves.

Next, if we explain the principle of self-excited operation,
If the operational amplifier 9 is positively saturated and the voltage at the terminal 8 is the saturation voltage Vs()O'), the excitation current flows through the resistor 7, through the winding 2, and into the ground G. At this time, an induced voltage is generated in the winding 3 through the magnetic core 5. The polarity of this induced voltage is positive on the 3a terminal side, so
Non-inverting terminal 1 of operational amplifier 9. A positive voltage is input to Ob, and as a result, the operational amplifier 9 outputs a positive saturation voltage Vs
keep coming out. During this time, the magnetic core 5 is still being excited, and while it is being excited until it reaches the maximum magnetic flux density of 1 noher Bm, the magnetic permeability of the magnetic core 5 gradually decreases.
As the induced voltage decreases, the coil impedance of winding 3 also decreases extremely. At this time, in this case, capacitor 6
The charge that had been charged by the induced voltage will be discharged. However, since the capacitor 6 and the winding 3 constitute a resonant circuit, the voltage on the 3a terminal side of the winding 3 changes from positive to negative voltage, and the non-inverting voltage of the operational amplifier 9 changes. A negative voltage signal is input to the terminal lOb, and the output voltage e of the output terminal 8 is input. automatically switches to negative DC saturation voltage -Vs. Then, at the next moment, the magnetic flux density level in the magnetic core 5 quickly returns to the level defined by the input current Iex, and then, due to the negative saturation voltage Vs, the magnetic flux density level in the magnetic core 5 is reduced to the negative maximum magnetic flux density level - B
It will change towards m. At this time, 3a of winding 3
Since the voltage at the terminal is, of course, negative, the output voltage e of the operational amplifier 9. is maintained at -Vs, and the capacitor 6 is charged with an electric charge due to the induced voltage.

When the magnetic flux density level of the magnetic core 5 reaches the negative maximum magnetic flux density level -Bm, the capacitor 6 starts discharging, and then due to the resonance phenomenon, the non-inverting terminals 1. Ob is an input voltage signal with inverted polarity (>0)
is input, and the output terminal voltage e.

is switched to the positive DC saturation voltage V8.

In this way, the driving DC voltage ±Vc applied to the operational amplifier 9 receives the voltage signal induced in the operational amplifier input winding of the magnetic core 5, and the output terminal 8 of the operational amplifier -9 receives the voltage signal induced in the operational amplifier input winding of the magnetic core 5.
In addition to alternately outputting the saturation voltage ±Vs, the saturation voltage waveform having both polarities (positive period and 9
The period length ratio (Tutee ratio) with the period is the measured current fi
It will be controlled by n.

The function of the capacitor 6 can be replaced by the stray capacitance existing between the windings by appropriately selecting the diameter of the windings and the number of turns wound around the magnetic core 5. In this case, it is obvious that the container 6 does not need to be installed.
0 is the display circuit section, and the square wave output voltage e. ge, buffer]
2 is inputted to the non-inverting terminal lJ, (/C) or is input to the non-inverting terminal I5 of the operational amplifier I6 for gain adjustment through an integrating circuit or a low-pass filter (not shown) consisting of a resistor 13 and a capacitor 14, Width increases.

Resistors 17 to 20 are connected between the output terminal, the inverting terminal, and the ground terminal of the operational amplifier 16 so that the degree of increase in the operational amplifier 16 can be selected depending on the strength of the current to be measured Iex. In addition, the circuit is configured so that the operational amplifier '16 operates as a comparator immediately after the circuit consisting of the resistor 13 and the capacitor 14, and the presence or absence of the current to be measured can be detected as the output voltage Eo at the low level. It is possible.

21 is a capacitor inserted for the purpose of removing unnecessary AC noise components. 22 is the increase in intensity A.

B and C are optional, (t (1 is a selector switch that cannot be selected. 2:3 is an indicator that has the function of displaying the polarity and strength of the current. 24 is a variable resistor. , adjust the current value flowing into the indicator 23.

200, the drive circuit section is a supply source of positive and negative direct current constant voltage ±Vc for the operational amplifier. FIG. 7 shows an embodiment of a modified circuit for stably executing the self-excitation operation of the current sensing section 100 shown in FIG. 6 even after application of a strong magnetic field.

The impedance 25 in FIG. 7(a) means a resistor or a capacitor, or a parallel connection circuit consisting of a resistor and a capacitor. Operational amplifier 90 inverting terminal] Oa is
It is connected to the terminal 2b of the winding 2, and recovery from the self-excitation stop phenomenon that occurs due to the application of a strong magnetic field is carried out by the negative feedback effect of the terminal voltage of 25.

In FIG. 7(b), the negative feedback effect by the impedance 25 is separated from the winding 2 and implemented by a series circuit with a variable resistor 26.

FIG. 8 shows an example of application of the present invention. current sensor 1000
As for the circuit configuration, an integrating circuit is connected after the current sensing section 100, a conbarrel is connected after the current sensing section 100, and the LE
The case of displaying as D is shown.

That is, a comparator that receives the output voltage of the integrating circuit as an input signal is connected, the input signal level is checked against a preset reference voltage value, and this is converted into a high-level or low-level signal voltage and output. As the comparator used here, it is sufficient to use a known comparator (including a window comparator), and it is sufficient to use it by taking advantage of its characteristics according to each purpose. Then, depending on the output of the comparator, for example, a relay that generates an alarm sound is operated or an LED is displayed.

Figure 8 (a) shows the make state C0N in the electromagnetic relay)
Here is an example of how to use it to reliably detect that current is flowing. By incorporating the entire current sensor into an electromagnetic relay and checking the presence or absence of current flowing through each contact,
It becomes possible to configure a self-diagnostic electromagnetic relay that detects abnormalities in operation. In this case, it is possible to use a single power supply (for example, 24V), and the ground G in Figures 6 and 7 can be raised to a voltage level that is half that of a single power supply (and
Alternatively, it is obvious that this can be easily achieved by creating an intermediate potential point using a voltage dividing circuit such as a resistor. Figure 8 (b
) is an example of application for determining the disconnection status of lamps, etc.

In some cases, the lighting status of various lamps L in a car cannot be checked directly from the driver's seat. Therefore, if a current sensor 1000 with a warning lamp is placed in the driver's seat, the lighting state of the lamp can be confirmed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the material composition of a single-hole magnetic core 1 made of a single-hole magnetic material used in the present invention, and FIG. 3 is a diagram showing the basic configuration of the winding wire, FIG. 3 is a diagram for explaining the operating principle of the present invention using the B-1ex characteristics of the magnetic core 4, FIG. 4 is a circuit diagram of the current detection section, Figure 5 shows ■ex = 0, I'ex in Figure 3)
A diagram of the voltage waveform e at the terminal in each case of 0.1''ex (O). Figure 7 shows an example of the overall circuit consisting of a display circuit that integrates and amplifies the output of the current sensing part, and Figure 7 shows that the self-excitation operation of the current sensing part shown in Figure 6 can be performed stably even after a strong magnetic field is applied. Figure 8 is a diagram showing an example of a modified circuit. 4. Input winding, 5.
Magnetic core with fixed winding, 6 capacitor, 7 variable resistor,
8 output terminal, 9 operational amplifier, 10 a - inverting terminal, 10 b non-inverting terminal, 40 minutes' worth of fluid, 100... current sensing part, 200 - drive part, 300 display circuit part, G - ground. Agent: Patent attorney Masamitsu Akizawa and two others. Figure 3, Figure 71'4 (c) Figure 5

Claims (1)

[Scope of Claims] (1) A single-hole magnetic core that collects the magnetic field generated by the current to be measured along the direction of the magnetic path around the hole of a perforated magnetic material, and an excitation tube wound around the magnetic core. a first winding, an operational amplifier for exciting the magnetic core, a second winding for inputting the operational amplifier wound around the magnetic core, the first winding to the output terminal side circuit of the operational amplifier, and the second winding to the output terminal side circuit of the operational amplifier. A magnetic semiconductor coupling circuit is configured by connecting to the input terminal side circuit, and the voltage signal between the terminals of the second winding is applied between the inverting input terminal and the non-inverting input terminal of the operational amplifier, so that the current to be measured is A self-oscillation type current sensor characterized in that it is capable of converting a saturated direct current constant voltage having bipolar polarities into a change in the tutee ratio of an operational amplifier. Self-oscillating current sensor. (:() A self-excited oscillation type current sensor according to claim 2, in which only the entirety of the current to be measured passes through the magnetic core. A self-oscillation type current sensor according to claim 1 or claim 2, wherein one magnetic core passes through the self-oscillation type current sensor.