JPS6244366Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current measuring circuit having a structure suitable for semiconductor integrated circuits.

Current measuring circuits used for general industrial purposes often use AC generators using wire-wound transformers or Hall elements, and both of these circuits apply the principle of magnetic circuit coupling. Therefore, these current measuring circuits are not suitable for compactness or mass production, and furthermore, there are significant restrictions on frequency characteristics.

The present invention was devised in view of the above-mentioned circumstances, and it is an object of the present invention to provide a current measuring circuit which is compact and has a structure excellent in mass production, and which can measure large currents easily and accurately.

Hereinafter, in explaining embodiments of the present invention with reference to the drawings, we will first discuss what points were focused on in realizing the present circuit. In general industrial use, problems arise when measuring large currents. In other words, it is often difficult to directly measure large currents such as 0 to 5 A, 0 to 10 A, or 0 to 30 A, so it is necessary to measure small currents proportional to the current, such as 0 to 5 mA, or 0 to 30 A. ~10mA, 0~
It is customary to divide the current into 30mA and measure it.

This invention focuses on the above-mentioned diversion,
The aim is to realize this using semiconductors to create a structure that is accurate and has wide applicability, and to use it for measuring current.

Hereinafter, a DC current measuring circuit will be explained with reference to FIG. In the figure, IC _D is a diode array produced in an integrated circuit structure. The internal structure of this diode array IC _D has a transistor configuration, but in reality it consists of multiple diodes D ₁ ,
The bases and emitters of D _{2 .} . . are connected in common, and the bases and emitters are forward biased.

_A1 is an operational amplifier with high gain. This operational amplifier _A1 may be formed on the same chip as the diode array IC _D constituting the current transformer, depending on the case. Furthermore, this operational amplifier
The reason for providing A ₁ is to accurately operate as a current shunt without causing an extra voltage drop at the branch of the forward diodes D ₁ , D _{2 .} . . that measure the current.

Therefore, in the current measurement circuit as described above, the forward voltage drop V _be of the diodes D ₁ , D ₂ ... is V _be = (KT/q)ln (I _c /I _s )...(1) . Here, K is the Boltzmann constant, T is the absolute temperature, q is the elementary charge, I _s is the saturation current determined by the shape of the diode, and I _c is the collector current (emitter current). Typically, the forward voltage drop V _be is determined by the silicon PN structure and is approximately 0.5V. In the Schottky barrier structure, it is around 0.3V.

By the way, each diode D ₁ , D ₂ shown in FIG.
If the patterns of ... have almost the same characteristics and shape, and the bases and emitters of the diodes D ₁ , D ₂ ... are connected in common, (1)
Since the I _s in the equations are all equal, the forward voltage drops V _be can also be made equal. In general, the variation in V _be of devices manufactured using advanced quality processes is 2 to 2.
It is 4mV or less.

Therefore, each forward diode D ₁ , D ₂ , ... of the diode array IC _D viewed from the current source i _r becomes a parallel element with equal voltage drop, and each forward diode
The current flowing through D ₁ , D ₂ , . . . is i _r /n. In other words, if you measure a single branch current i ₁ , i ₂ , ... of the same shape with n diodes D ₁ , D ₂ , ...D _o installed in parallel, the current will be shunted to the desired value, i.e., i _r /n. The current can be measured, and in turn, the current input to this diode array IC _D can be measured.

Next, referring to FIG. 2, it will be described that the shunt current can be accurately measured without causing an extra voltage drop at the branch of each diode D ₁ , D ₂ , . . . That is,
Figure 2 shows the output stage or operational amplifier shown in Figure 1.
This is an extracted part of A ₁ , and in the same figure, the output voltage e _p is e _p =e _i・A _p (however, A _p
However, since the open loop voltage amplification A _p in the operational amplifier A ₁ is virtually infinite,
e _i =OV.

Similarly, since the input impedance Z _io is infinitely large, the input current i _b of the operational amplifier A ₁ itself
can be ignored as i _b <<i _o , so if i _f =i _o
becomes. Therefore, when measuring the shunted current, you can connect the measuring device to the feedback loop of the operational amplifier A ₁ without causing an extra voltage drop at the branch of each diode D ₁ , D ₂ , etc. This means that the i _r /n current can be measured accurately. For example, if a resistor R _f is inserted into the feedback loop, a voltage of e _p =i _o ·R _f = i _r /n · R _f (2) can be generated, and a voltage proportional to the input current i _r can be measured. Note that it is well known that this current-voltage conversion is performed by the operational amplifier _A1 .

As is clear from the above description, the diode array IC arranged geometrically equally allows its branch current to be measured by the operational amplifier _A1 with an input voltage drop of OV. Regarding temperature fluctuations, the V _be itself of each diode D ₁ , D ₂ , ... fluctuates with a characteristic of about -2 mV/C, but all the diodes D ₁ , D ₂ , ... are on the same silicon substrate. Therefore, it has an extremely high temperature correlation and does not affect the branching ratio of each branch current.
Therefore, in a circuit with this configuration, for example, 1000 equal diodes D ₁ , D ₂ , . . . are included in the same IC chip.
If D ₁₀₀₀ is generated and the branch current at one terminal is measured, the input current i _r can be reduced to 1/1000 and measurement can be made, thereby making it possible to measure large currents.

Next, FIG. 3 is a diagram showing another example of the circuit shown in FIG. 1, in which the diodes D ₁ , D ₂ . . .
Focusing on the current measurement means using the same diode D ₁ ,
It is constructed using a transistor array IC _T instead of D ₂ . In this case as well, the transistor
Each transistor T ₁ , T ₂ ... in the chip of array IC _T
If they have substantially the same characteristics and substantially the same shape, I _c in equation (1) will all be equal, and the forward voltage drops V _be between the base and emitter will have the same value.

Then, as shown in the figure, multiple transistors
If a collector bias e is applied only to any transistor T _o among T ₁ , T ₂ , ..., the transistor T _o operates as a common base circuit (impedance conversion circuit), and from i _co = β・i _bo ∴i _bo =i _co /β. Also, i _co =i _eo -i _bo , and if β is made very large, ∴i _co = i _eo = i _o . By the way, each transistor T ₁ , T ₂ ,...
If the shapes of the transistors T _o
Since the branch current i _o of is ∴i _o = i _r /n, the collector current i _c of the transistor T _o
If _o is measured, this means that it is measured as a current proportional to the input current _ir .

Therefore, if you insert a load resistor R _L into the collector branch of the transistor T _o and measure the voltage drop, you will get a voltage V proportional to the input current, that is, V =
The value i _r /n·R _L can be measured.

In this way, in the current measuring circuit shown in Fig. 3, _{the base and collector of each transistor T 1 , T 2} . and multiple transistors by connecting them on a common line.
Since T ₁ , T ₂ . . . are arranged so as to have substantially the same characteristics and substantially the same shape, by impedance conversion of the branch current with a grounded base circuit and measurement, a value proportional to the input current can be determined.

Next, FIG. 4 shows another embodiment of the present invention, which was designed to solve the inconvenience caused by the lack of insulation between input and output as shown in FIGS. 1 and 3. This is a configuration example. In other words, the figure shows transistor array IC _T (diode array IC _D
A photocoupler P is provided at the output stage of the input and output devices to insulate the input and output and measure the current. In other words, by connecting the light emitting element of the photocoupler P to the collector side of the transistor T _o whose base is connected to ground, and measuring the current i _p of the light receiving element on the secondary side, the current can be measured while being isolated from the input side. can.

Now, in FIG. 4, if the current flowing through the light emitting element of the photo coupler P is i _co , as described above, i _co = i _r /n. As a result, the current i _p on the light receiving element side of the photo coupler P becomes i _p =η·i _co (where η is the transmission rate), and a current proportional to i _co can be measured as i _p .

Next, FIG. 5 shows an example of bidirectionally connecting a diode array IC _D to measure current as an AC current transformer. In this case, the equivalent circuit seen from the current source i _r side is as shown in FIG. On the other hand, when applied to the DC transformer shown in FIG. 1, the equivalent circuit becomes as shown in FIG. 7. As is clear from the above equivalent circuit, it is sufficient to simply connect the diodes with opposite polarities.

At the same time, a desired shunt ratio can be obtained by changing the connections of a large number of diodes as shown in FIG. This diode D ₁₁ ,
D ₁₂ ,..., D _1o , D ₂₁ , D ₂₂ ,..., D _2o are formed on the same chip, and half of them, for example,
D ₂₁ , D ₂₂ ,..., D _2o only external switches S ₁ , S ₂ ,
...If you change the connection at S _o , you can measure the current at the desired split ratio as an AC current transformer.

Note that the connections of the diodes D ₂₁ , D ₂₂ , ...D _2o can be changed by taking them out to the outside depending on the available pins when integrated into an IC. This may cause the PN junction to collapse. In other words, it is possible to form as many elements as possible on a chip during initial production, and to crush unnecessary diodes in the final manufacturing stage. This allows for example
Even if 1/1000 diversion is possible by forming 1000 diodes in advance, it is possible to change the diversion ratio to 1/900 by crushing 100 diodes with a metal mask.

Next, FIG. 9 shows an example in which an AC current transformer is constructed using a transistor array IC _T. This case can also be easily realized by connecting the DC transformers in a bidirectional manner as in FIG. 5. That is, at the terminals P and N, the P-side transistors T ₁₁ , T ₁₂ , ...T _1o are turned on in the positive half cycle, and the photo coupler is turned on.
A current i _p flows through the photodetector side through P ₁ , and in the negative half cycle, the N-side transistor T ₂₁ ,
T ₂₂ ,..., T _2o are turned on, and a current i _p2 is caused to flow through the photo coupler P ₂ to the photodetector side, thereby causing a current proportional to the input current i _r to flow through the secondary load resistance R _L. It was designed to flow.

In addition, as a diode array configuration using another integrated circuit, the shapes of the emitters are made equal as shown in FIG. 10, and the current flowing through each emitter branch is made equal, so that the shunted current i _o can be measured. is also possible.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and that various modifications can be made without departing from the gist thereof.

As detailed above, according to the present invention, it is possible to form multiple semiconductor elements in the same pattern on the same chip so as to form a current transformer configuration, so that it can be manufactured as an integrated circuit using IC technology. I can do it. As a result, current can be measured with high accuracy due to uniform manufacturing. In addition, since current is measured simply by combining semiconductors without coupling magnetic circuits as in the past, the compact configuration makes it ideal for cost reduction and mass production. , it is also possible to improve frequency characteristics. Furthermore, if semiconductors are integrated, a considerable number of semiconductors can be formed on the same chip, thereby providing a current measuring circuit that can relatively easily and accurately measure large currents on the input side.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the current measuring circuit of the present invention using a diode array, Figure 2 is a diagram explaining the output circuit of Figure 1, and Figures 3 and 4 are the diagram of the current measuring circuit of the present invention using a transistor array. A block diagram explaining another example of the circuit, FIG. 5 is a block diagram explaining another example applied to an AC shunt, and FIGS. 6 and 7 show equivalent circuits of FIGS. 1 and 5. 8 to 10 are configuration diagrams illustrating other embodiments of the circuit of the present invention. IC _D ... Diode array, D ₁ , D ₂ ... Diode, A ₁ ... Operational amplifier, IC _T ... Transistor array, T ₁ , T ₂ ... Transistor, P,
P ₁ , P ₂ ... Photo coupler.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) In a circuit that measures input current supplied from an external source, each base is common and the emitter is connected to a common line, and the input current is input between this common base line and the emitter common line. It has n semiconductor elements having almost the same characteristics and almost the same shape, which divides the input current into 1/n, and an amplifier having a high open-loop gain, and extracts the current flowing through a part of these semiconductor elements. and an output circuit that makes it possible to measure the input current. (2) The current measuring circuit according to claim (1) of the utility model registration, wherein the output circuit is connected by a photocoupler and a shunt current is transmitted to the output circuit. (3) Utility model registration claim No. (1) which has two sets of multiple semiconductor element groups having a common base and which are connected to each other so as to have bidirectionality so as to shunt an alternating current input current. Current measurement circuit described in section.