JPH01232807A - Current comparison circuit - Google Patents

Abstract

PURPOSE:To set a reference current freely with high accuracy in response to the application and to attain the comparison with high accuracy by using a constant current circuit whose current is set optionally by a resistor as the reference current source. CONSTITUTION:With a power voltage applied to a power terminal 1 in a current comparator circuit, a current expressed in equation flows to a collector of a transistor(TR) Q1, where V1 is a constant voltage of a constant voltage source 5'. Since TRs Q2, Q3 constitute a current mirror, a collector current of the TR Q3 is nearly equal to a current I1 and the current I1 is the reference current. When a current IIN flows from the input terminal in case of IIN<I1, the current corresponding to (I1-IIN) flows to the emitter of a TR Q5. Thus, a TR Q6 is conductive and an output 4 reaches a low level. On the other hand, in case of IIN>=I1, the TR Q6 is nonconductive and the output 4 goes to a high level. Thus, the quantity of the current IIN with respect to the current I1 is compared by the circuit comprising the TRs Q4, Q6 and the result is discriminated by the turn-on/turn-off of the TR Q6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current comparison circuit, and particularly to a current comparison circuit that determines whether an inflow or outflow current value input to the circuit is large or small relative to a certain value.

[Conventional technology]

As a current comparison circuit of the above type, the present applicant has filed a patent application filed in 1983-
No. 107009 proposes a current comparison circuit shown in FIG.

In Figure 2, 1 is a power supply terminal, 2 is an input terminal, 4 is an output terminal, 5 is a constant voltage source, 6 is a constant current source, Q4 and Q6 are N
PN transistor, Qs is PNP transistor, R
2 and R3 are resistors.

In FIG. 2, when a certain value of current ■ flows out from input terminal 2, if 11 is smaller than the output current ■2 of constant current source 6, the current of the difference (I211) is
becomes conductive and transistor Q4 becomes non-conductive, so that it flows into the emitter of transistor Q5. As a result, the base potential of the transistor Q6 becomes higher than the forward voltage of the transistor due to the collector current of the transistor Q5 and the voltage drop caused by the resistor R2, so that the transistor Q6 becomes conductive and the output 4 becomes a low level.

On the other hand, if current 11 is equal to or greater than I2, transistor Q is non-conducting and transistor Qs
The collector current of becomes 0. Therefore, the base voltage of transistor Q6 is at ground level, transistor Q is non-conductive, and output 4 is at high level. At this time, 1l=I2
In this case, the transistor Q4 is also non-conductive, but when I>I2, the current of the difference (11-I2) is supplied from the emitter of the transistor Q4.

As mentioned above, in the circuit of Fig. 2, the input current ■I of 1
2 is compared with the transistor Q 4 +Q, and the result is determined as an on/off result of the transistor Q6.

[Problems to be solved by the invention] The present invention relates to an improvement of the current comparison circuit shown in FIG. 2 above,
It is an object of the present invention to provide a circuit suitable for implementation in an IC, which can arbitrarily set the constant current value to be compared.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of a current comparison circuit according to the present invention, and the same components as in FIG. 2 are given the same symbols. In the figure, 3 is a terminal to which a resistor for determining the reference current value is connected, 5' is a constant voltage source, Q+ is an NPN transistor, Q2. Q3 is a PNP transistor having a current mirror configuration, and R1 is a resistor connected to the terminal 3.

In FIG. 1, it is assumed that the components other than the resistor R1 are integrated circuits, and the resistor R1 is externally attached.

In the configuration shown in FIG. 1, a power supply voltage is applied to 1 and 5
If the constant voltage value of ' is vl, a current of l flows through the collector of the transistor Q1. Transistors Q2 and Q3 form a current mirror, so if you ignore the base current,
The collector current of transistor Q3 is I.

approximately equal to. Therefore, 11 becomes the reference current value of this current comparison circuit. Here, when currents I and H flow out from the input terminal, if I and N<I, the current for (1, -1, N) causes transistor Q to conduct and Q4 to non-conduct. As a result, the current flows into the emitter of the transistor QIs. With this, the collector current of transistor Q and R2
Due to the voltage drop caused by this, the base potential of the transistor Q6 reaches the forward voltage of the transistor Q6, the transistor Q6 becomes conductive, and the output 4 becomes a low level.

On the other hand, when 11N≧11, the transistor Q becomes non-conductive and the collector current of the transistor Q6 becomes zero. Therefore, the base voltage of transistor Q6 is at ground level, transistor Q6 is non-conductive, and output 4 is at high level. At this time, I, N=1. In this case, transistor Q4 is also non-conducting, but 11N>1. Well then (IIN It
) is supplied from the emitter of transistor Q4 when it becomes conductive.

As described above (in this embodiment, the reference current 11 is determined by the resistor R8, and the 1.
A comparison is made between the transistors Q41 and Qls based on the configuration of the transistor Q41Qls, and the result is determined as an on/off result of the transistor Q6.

Note that a variable resistor may be used as the resistor R8.

〔Effect of the invention〕

As explained above, by using a constant current circuit with a structure in which the current value can be arbitrarily set using a resistor as a reference current source, a current comparison circuit that can freely and accurately set the reference current according to the application can be realized. In particular, when this circuit is integrated into an IC, the advantages of externally connecting the current setting resistor can be greatly improved.Also, as mentioned above, the current comparison circuit of the present invention can be used to adjust the magnitude of the current value. Since the magnitude is determined only by comparison, it is possible to perform comparison with higher precision than in the conventional voltage conversion comparison method.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a current comparison circuit according to the present invention, and FIG. 2 is a circuit diagram showing a current comparison circuit according to a prior application. l is a power supply terminal, 2 is an input terminal, 3 is a current setting resistor connection terminal, 4 is an output terminal, 5 and 5' are constant voltage sources, 6 is a constant current source, Q, ~Q6 are transistors, R0 ~ R3 is resistance.

Claims (1)

[Claims] The base of the first NPN transistor is connected to a constant voltage source, a resistor is connected between the emitter of the first NPN transistor and GND, and the collector and base of the first PNP transistor are connected to the collector of the first NPN transistor. and,
A constant current circuit having a structure in which the base of a second PNP transistor is connected, the emitters of the first and second PNP transistors are connected to a power supply, and the collector of the second PNP transistor is an output is used as a reference current source. A current comparison circuit characterized in that the reference current value can be arbitrarily set by making the resistance value variable.