JPH01295175A - Current measuring circuit - Google Patents

Abstract

PURPOSE:To keep an insulation and to exactly measure a current by using a photo-coupler for transmitting the current to be measured and the photo- coupler for transmitting a reference current, and measuring the current in comparison with both outputs. CONSTITUTION:On connecting light emitting diodes L1 and L2 of the photo- couplers 4, 5 and 7, 8 which are formed on the same tips 3, 6, with a shunt resistance R2 in series and also connecting this with a shunt resistance R1, then half cycle currents of plus and minus are made to flow into the light emitting diodes L1, L3. Also, the light emitting diodes L2, L4 are connected through controlling resistances VR1, VR2 with a power source VCC. And, the currents flowing in the light emitting diodes L1 and L2 are read by comparing an output V11 with V12 and V21 with V22 of the photo-coupler. By this method, it is able to know a monetary absolute value of the current flowing in a load 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field
This invention relates to a current measurement circuit that can be easily measured.

(B) Prior Art Conventionally, when measuring the current flowing in a circuit to which a high voltage is applied, the current to be measured i is passed through a current detection resistor 51 as shown in FIG. The voltage at both ends is detected by the voltage detection unit 52, and the detected voltage is applied to the V/F converter 5.
3, it is converted into a frequency signal and transmitted to the signal processing section 56 by the photocoupler 55.

Another current measurement technique, as shown in FIG. 6, is one in which the current to be measured i is passed directly to the primary side of a photocoupler 61, and the photocoupler 61 transmits a signal to a signal processing section 62.

(c) Problems to be Solved by the Invention Of the above-mentioned conventional techniques, the measuring circuit shown in FIG. It has to be floated off the ground while maintaining the same temperature, and the power supply that drives the whole thing has to be kept under high voltage, which not only poses many safety problems, but also makes the circuit configuration expensive.

In addition, since the measurement circuit shown in Figure 6 has only one photocoupler as the detection section, there is no guarantee that the transfer characteristics of the photocoupler are constant, and even if it is possible to "detect current", there is a problem that accurate measurement cannot be made. .

This invention has been made in view of the above-mentioned problems, and it is possible to measure the current flowing in a circuit to which a high voltage is applied with high accuracy without floating most of the circuit under high voltage. The object of the present invention is to provide a current measuring circuit that can be used.

(d) Means and operation for solving the problem The current measuring circuit of the present invention includes a plurality of photocouplers having the same characteristics or between paths, and transmits the current to be measured using at least one first photocoupler, A reference current that can be accurately measured is transmitted by at least one other second photocoupler, and the current to be measured is measured based on the outputs of the first photocoupler and the second photocoupler. .

In this current measurement circuit, since the current to be measured is transmitted using a photocoupler, there is no need to float the secondary side of the photocoupler, that is, most of the measurement circuit under high voltage. Also,
Since the first photocoupler transmits the current to be measured, and the second photocoupler transmits a reference current that can be accurately measured, the current to be measured can be accurately measured by comparing the outputs of the first and second photocouplers. .

(E) Examples The present invention will be explained in more detail with reference to Examples below.

<Example 1> FIG. 1 shows an example of the present invention. This example is
This is a circuit that measures the alternating current flowing through a general commercial power supply (AC 100V) line. In FIG. 1, an alternating current i is passed from the AClooV power source to the load 2 and shunt resistors R3 and R2. Furthermore, a photocoupler 4.5 formed on the same chip 3 and therefore having the same characteristics, and a photocoupler 7.8 also formed on the same chip 6 are provided, and the shunt resistor R2 is connected to both ends of the shunt resistor R1. A parallel circuit of light emitting diodes L+ and R3 of the photocoupler 4.7 is connected in series and connected in parallel. The light emitting diodes L and R3 are connected with opposite polarities to each other so that a positive half-cycle shunt current flows through the light emitting diode L1, and a negative half-cycle shunt current flows through the light emitting diode L3. In addition, the DC power supply voltage CC of the circuit is connected to the anode of the light emitting diode L2 of the photocoupler 5 via an adjustment resistor VR, and is also connected to the anode of the light emitting diode L4 of the photocoupler 8 via an adjustment resistor VR2. has been done. The cathodes of light emitting diodes L2 and R4 are connected to ground GN.
Connected to D. On the other hand, photocoupler 4.5.7.8
A power supply VcC is connected to the collectors of each of the phototransistors PT, PT2, PT3, and PT4, and resistors R, , R2, R, , R, are connected between each emitter and the ground GND. The resistance values of these resistors R1, . . . , R4 are set to be equal. Each phototransistor PT,
,..., PT, the output voltages V ll, V I 2, ■ corresponding to the transmission currents of photocoupler 4.5.7.8
21% ”22 is derived.

Now, focusing on the photocoupler 4.5, the output voltage ■18, V1
2 is observed with an oscilloscope, the waveform shown in FIG. 2 is obtained. Here, when the adjustment resistor VR is changed, ■1□ in the same figure goes up and down, but at this time, the current flowing through the primary side of the photocoupler 5, that is, the upper 2 side of the light emitting diode, is
It can be easily determined by Vcc"0.7/VR (where 0.7 is the contact potential difference of the light emitting diode), but it can be easily determined by inserting an ammeter in series with lJ and the adjustment resistor VR. Using this current as a reference (reference current), the instantaneous value of the current flowing through the light emitting diode L1 side of the photocoupler 4 can be found by comparing the output voltages V1 and V12 of the photocoupler 4.5. 8
By looking in the same manner as above, it is possible to know the waveform of the current flowing through the target AC 100V line and its instantaneous absolute value.

<Embodiment 2> FIG. 3 is a circuit connection diagram of a current measuring circuit showing another embodiment of the present invention. In the same figure, the light emitting diode L1 of the photocoupler 4 formed on the same chip 3 is connected to the power supply line through which the measurement current i+ flows, and the other photocoupler 5
Connect the anode of the light emitting diode L2 to the +V ec power supply, and connect the cathode of the light emitting diode L2 to the ground GND.
A transistor Tr and a resistor Re are connected between them.

In addition, phototransistor PT of photocoupler 4.5, ,
A +V cc power supply is connected to the collector of PT2, and resistors R, R4 of the same value are connected between the emitters of phototransistors PT1 and PT2 and the ground, respectively.

The emitter of the phototransistor PT is connected to one input terminal of the error amplifier 9, and the emitter of the phototransistor PT2 is connected to one input terminal of the error amplifier 9. The output terminal of the error amplifier 9 is connected to the transistor Tr via the resistor R7.
connected to the base of.

In this example circuit, when the measurement current il is passed through the power supply line, that is, the primary side of the photocoupler 4, and the reference current 12 is passed through the primary side of the photocoupler 5, each current +1.12 is caused by the photocoupler 4.5, and the secondary Transmitted to the side, the current 11
, +2 is output and input to the error amplifier 9. The error amplifier 9 outputs a voltage according to the difference between the re-inputs, and the transistor Tr is controlled so that this difference voltage becomes O. Due to this automatic control function, the current 12 flowing through the transistor Tr is always kept equal to the desired measurement current il. Therefore, by measuring the current 12 with, for example, an ammeter, the measured current 11 can be determined.

<Embodiment 3> FIG. 4 is a circuit connection diagram of a current measuring circuit showing still another embodiment of the present invention. This embodiment is an example in which the present invention is applied to a constant current power supply for electrophoresis. In this example,
A chopping transistor circuit 11 that converts DC input into an AC signal in order to flow a constant current to the load 2, an oscillator 13 that performs the chopping operation, a transformer T, and a rectifier circuit that rectifies the AC voltage converted by the transformer T. 12
The circuit section consisting of is a normal switching regulator. The other circuit parts are equipment for electrophoresis experiments, which is a characteristic part of this example, and the output is high voltage, and the power supply polarity differs depending on the experimental conditions, so it is necessary to be able to select it arbitrarily. be. The current signal transmission system in this embodiment uses two photocouplers 4.5 formed on the same chip 3, as in FIG. This current 11 is transmitted by the photocoupler 4, and the current iI
The voltage is converted into a voltage according to the voltage, outputted, and applied to one input terminal of the error amplifier 9. On the other hand, +Vcc power is applied to the photocoupler 50 light-emitting diode L2 via the adjustment resistor (setting device) VR, and the flowing current 12 is transmitted by the photocoupler 5, converted to a voltage corresponding to the power supply 12, and output. and is applied to the other input terminal of the error amplifier 9. The error amplifier 9 amplifies the re-input differential voltage,
It is fed back to the pulse width modulation circuit 14.

In this embodiment circuit, the current to be passed through the load 2 is set by adjusting the adjustment resistor VR. The set current 12 is transferred from the light emitting diode L2 to the phototransistor P T 2
is transmitted, and the output of photocoupler 5 is transmitted.

The power is input to an error amplifier 9. On the other hand, the current 11 flowing through the load 2 is transmitted from the light emitting diode L to the phototransistor PT, and the output of the photocoupler 4 is transmitted to the error amplifier 9.
is input. The error amplifier 9 amplifies the difference voltage between the outputs of the photocouplers 4 and 5 and inputs it to the pulse width modulation circuit 14.

If the values of the set current 12 and the load current 11 are different, since the photocouplers 4 and 5 have the same characteristics and the resistors R3 and R4 are set to the same value, the output of the photocouplers 4 and 5 will be the current flowing to the primary side, respectively. Therefore, the error amplifier 9 outputs a voltage according to the difference between the set current 12 and the load current i+, which is input to the pulse width modulation circuit 14, which is eventually fed back to the phase width of the chopping transistor, and finally In other words, the load current 11 is controlled so that it becomes f't L t,2, that is, the target set current.

In each of the above embodiments, the photocouplers for transmitting the current to be measured and the photocouplers for transmitting the reference current are formed on the same chip and have the same characteristics. However, in this invention, both photocouplers are , independent parts having substantially the same characteristics may be selected in advance and used.

In addition, in Example 3, the set current is set to a constant value and the output is controlled to be constant, but by using a gentle alternating current as the set current, it can be used to control isolated high voltages and large currents with arbitrary gentle waveforms. You can also.

(F) Effects of the Invention According to this invention, since the current flowing in the circuit to which high voltage is applied is transmitted using a potocoupler, most of the measurements can be performed while electrically insulating the high voltage circuit. A circuit can be configured, and therefore a safe measuring device can be realized at low cost.

Furthermore, in addition to the first photocoupler for transmitting the current to be measured, a second photocoupler for transmitting a measurable reference current is provided,
Since current is measured by comparing the outputs of both photocouplers, relatively accurate measurements can be easily made.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing one embodiment of the present invention, and FIG.
3 is a waveform diagram for explaining the operation of the circuit of the embodiment, FIG. 3 is a circuit connection diagram showing another embodiment of the present invention, and FIG.
The figure is a circuit connection diagram showing still another embodiment of the present invention, and FIGS. 5 and 6 are circuit block diagrams showing a conventional example. 2: Load, 4, 5, 7, 8: Photocoupler, VR, ・VRz: gllll resistance 3, R4, R6, R6: Photocoupler output resistor. Patent applicant Shimadzu Corporation Representative Patent attorney Shigeru Nakamura

Claims (1)

[Claims] (1) A reference current that includes a plurality of photocouplers with the same or substantially the same characteristics, in which at least one first photocoupler transmits the current to be measured, and at least one other second photocoupler can accurately measure the current. 1. A current measuring circuit that transmits a current and measures a current to be measured based on the outputs of the first photocoupler and the second photocoupler.