JPH07947Y2 - Voltage applied current measurement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a voltage application current measuring circuit for applying a set voltage to a load and measuring a current flowing through the load.

[Conventional technology]

Conventionally, when measuring a current flowing through a load by applying a set voltage to the load, generally, a so-called VFM (Voltage Forcing Mean) is used.
Assurement) method of measuring with a power supply,
Alternatively, a simple method has been adopted in which an ammeter is inserted in series for measurement, or a resistance is inserted in series and the voltage drop of the resistance is measured by a voltmeter.

[Problems to be solved by the device]

The above simple method of inserting an ammeter or a resistor in series has a problem that an error of a voltage drop occurs due to the internal resistance of the ammeter or the insertion resistance with respect to the set voltage.

On the other hand, VFM that compensates for the voltage over the conventional set voltage range
The measuring circuit incorporating the power supply having the function of has a problem that the circuit configuration is complicated and expensive.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a circuit which has a simple circuit configuration and can perform measurement with a small error.

[Means for Solving the Problems]

The measuring circuit of the present invention uses a current mirror circuit, and by negatively feeding back the output from the collector of one transistor of the current mirror circuit to an operational amplifier, a voltage drop occurs when a forward current flows through the transistor. Current-voltage conversion circuit is connected to the collector of the other transistor of the current mirror circuit, and the set voltage is input to the non-inverting input terminal of the op-amp to input the current
The mirror circuit is configured to be applied to the load via the collector of the one transistor and to measure the current flowing through the load by the converted voltage appearing in the current-voltage conversion circuit.

〔Example〕

 FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, 1 is a voltage input terminal, 2 is operational amplifiers 3a and 3b, and transistors Q ₁ , Q ₂ and 4 are current mirror circuits.
Is a voltage output terminal, 5 is an operational amplifier, 6 is a resistor R ₁ , and 7 is a load.

When the set voltage V ₁ is applied to the voltage input terminal 1, this voltage is output as the voltage V ₃ to the voltage output terminal 4 via the output terminal of the operational amplifier 2 and the transistor Q ₁ . Since the transistor Q ₁ is diode-connected, V ₃ drops with respect to V ₁ by the diode forward voltage. In order to compensate for this, the output of the transistor Q ₁ is negatively fed back to the operational amplifier 2, V ₁ = V ₃ , and the set voltage V ₁ is applied to the load 7 without a voltage drop on the way.

Since the transistors Q _1, Q ₂ constitute a current mirror circuit, while the current I ₂ flowing in the current I ₁ and the transistor Q ₂ to which flows through the transistor Q ₁ is a direct current amplification factor of the transistor Q _1, Q _{2 Is} H _FE , When the relation of is established and H _FE is large enough, I ₂ becomes almost equal to I ₁ .

The current value flowing through the load 7 is obtained by measuring V ₄ (= −I ₂ R) obtained by converting the current I ₂ into a voltage by the current-voltage conversion circuit configured by the operational amplifier 5 and the resistor R ₁ .

As described above, since the setting voltage is applied to the load 7 and the current I ₂ that is almost equal to the current I ₁ flowing through the load 7 is converted into a voltage for measurement, measurement with less error can be performed.

2 and 3 are circuit diagrams showing other embodiments of the present invention.

In the figure, 1,2,3a, 3b, 4,5,6,7 are the same as or corresponding to the same reference numerals in FIG. 1, and 8,9 are transistors Q ₃ , Q
₄ and 10 are resistors R ₂ .

The one shown in FIG. 2 has the same basic operation as that of the embodiment shown in FIG. _1, and in order to further improve the approximation of the current I ₁ and the current I ₂ ,
This is the addition of transistor Q ₃ . In this case, the current
The relationship between I ₁ and I ₂ Becomes

In the case shown in FIG. 3, when the current flowing through the load 7 is relatively large, a transistor Q ₄ is added in order to compensate for the shortage of the output current of the op amp 2, and further, the mirror current I ₂ is added.
For the smaller, obtained by inserting the resistor R _2, the current I ₁
In contrast, the current I ₂ is The current is suppressed to.

Here, K: Boltzmann's constant, T: absolute temperature, q: electron charge amount. In this case, if the resistance R ₂ is increased, the sensitivity as an ammeter does not decrease.

Although each transistor is shown as a PNP transistor in the above description, it may be an NPN transistor.

Moreover, the input bias current of the operational amplifier 2 is B of the FET input.
If the i-FET type is used, the effect on the current mirror circuit can be ignored.

[Effect of device]

As described above, according to the present invention, it is possible to obtain a value that does not include an error caused by a voltage drop due to a resistor or the like with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2, and FIG.
Each of the drawings is a circuit diagram showing another embodiment of the present invention. 1 ... voltage input terminal, 2 ... operational amplifier, 3a, 3b, 8, 9 ...
... Transistor, 4 ... Voltage output terminal, 5 ... Op Amp, 6,10 ... Resistance, 7 ... Load, the same reference numerals in the drawings indicate the same or corresponding ones.

Claims (1)

[Scope of utility model registration request] 1. A voltage application current measuring circuit for applying a set voltage to a load to measure a current flowing through the load, wherein the set voltage is connected to a non-inverting input terminal of a first operational amplifier,
A current circuit configured to flow a current from the output terminal of the operational amplifier to the load whose one end is grounded via a diode-connected first transistor, wherein the voltage at the connection point between the first transistor and the load is the first A feedback circuit connected to the inverting input terminal of the operational amplifier to control the voltage applied to the load to be substantially equal, and a current mirror that forms a current mirror for the first transistor and has a current that is substantially the same as the current flowing through the first transistor. Is connected to the inverting input terminal of the second operational amplifier, the current output terminal of the second transistor is connected, the non-inverting input terminal of the second operational amplifier is grounded, and the output of the second operational amplifier is A current-voltage conversion circuit configured by connecting a resistor having a predetermined resistance value between the terminal and the inverting input terminal is provided. Voltage source current measurement circuit for a.