JPS62231322A - Constant current circuit - Google Patents

Abstract

PURPOSE:To make constant the variance of a first and second resistance values in an integrated circuit by the adjustment of the external resistance and to supply a constant current to a load by providing an external resistance at the external part of an integrated constant current circuit to supply a constant current to a load circuit. CONSTITUTION:At a constant current circuit, a constant power source by a transistor TRQ1 is provided, the collector of the TRQ1 is connected through a load circuit RL to a voltage source Vcc and an emitter is connected through the first resistance R3 to a earth potential. To the base of the TRQ1, the emitter of the TRQ2 is connected, the voltage source Vcc is connected through a resistance R1 to the connecting point and the emitter is connected to the earth electric potential. Further, an external terminal 1 is connected to the base of the TRQ2, connected through the third resistance R3 to the earth electric potential and the voltage source Vcc is connected through the second resistance R0 to the terminal 1. The voltage determined by the second and third resistance ratios R0/R2 is applied to the base of the TRQ2, and the influence of the dispersion of the resistance value of resistances R3 and R2 of an integrated constant electric current circuit is corrected.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a constant current circuit that supplies a constant current to a load circuit such as a differential amplifier, and particularly relates to a constant current circuit that supplies a constant current to a load circuit such as a differential amplifier. The present invention relates to a constant current circuit that eliminates variations in current due to errors in resistance values of resistors.

(Prior Art) An example of a constant current circuit used in an integrated circuit is shown in FIG. In this figure, transistor Q11 has a base with
The voltage supplied from the voltage source VCC is reduced to a predetermined level by a circuit consisting of resistors R11, R12 and a transistor Q12 (diode connected), and a voltage is applied to the load circuit RL connected to the collector side by a resistor R13 on the emitter side.
It is a constant current source transistor that supplies a current according to the following.

In other words, the change in the collector current of transistor Q11 due to the change in the base-emitter voltage V of transistor Q11 [or the voltage source VCC] is
12, a constant current is supplied to the load circuit R1-.

The above constant current (■) is expressed by the following formula.

Note that VF is the base-emitter voltage of the transistor when the circuit shown in FIG. 4 is integrated.

By the way, when the circuit shown in Fig. 4 is constructed from an integrated circuit, due to the nature of the integrated circuit, the base-emitter voltage `` and the resistance of the individual resistors (111) vary widely, but the ratio of the resistors R12/R11 etc. The variation is small. Therefore, in equation (1), the variation is V
cc/R13 and VF/R13, and it can be seen that the current I has variations due to these. Furthermore, the dispersion of the integrated resistance value is above 20%, and the temperature coefficient is 2000%.
[1111m/'C], and ■" variation is approximately ±0.1 [VF, temperature coefficient is -2[rr+V/"C]
] There is actual measurement data.

FIG. 5 shows another conventional example. Transistor Q13 corresponds to transistor Qll in FIG. 4, has a load circuit RL connected between its collector and voltage source VCC, and has a resistor R17 connected between its emitter and a reference potential point. transistor Q
14, a voltage determined by the resistance ratio of series resistors R14 and R15 connected between the voltage source VCC and the reference potential point is applied to the base, the collector is connected to the reference potential point, and the emitter is connected to the reference potential point through the resistor R16. Connected to voltage mVCC. The voltage generated at this emitter is supplied to the base of the transistor Q13.

This circuit determines the base bias of the resistor R14 from 1 to the resistor Q14 at [<15, etc.], thereby determining the base bias of the resistor R16
The current IR flowing through the collector-emitter path of the transistor Q14 drives the transistor Q13. For example, when the voltage source VCC fluctuates, the current IR controls the base current of the transistor Q13.
The current flowing through the load circuit R1 of No. 13 is made constant.

The current I in the case of FIG. 5 is as shown in the following equation.

Comparing Equation (2) with Equation (1), since it does not include a term that affects VF, it has the advantage of suppressing variations in current I, but variations due to resistor R17 remain.

(Problems to be Solved by the Invention) As explained above, constant current circuits based on integrated circuits suffer from variations in resistance within the integrated circuit.

Alternatively, no measures have been taken to deal with variations in the pace-emitter voltage V of the transistors or variations in the constant current I due to these temperature coefficients.

Generally, in constant current circuits used in integrated circuits,
The constant current ■ is given by the following equation (3).

However, α and β are coefficients determined by the resistance ratio, RA.

RB is a resistance inside the integrated circuit.

In such an integrated constant current circuit, there are variations in the resistance value of the resistor inside the integrated circuit and the base-to-rector voltage VF, and due to the nature of the integrated circuit, it is difficult to avoid variations in the internal resistance. However, there was a problem in that the constant current value varied. Note that the variation due to VF is the fifth
Although this effect can be eliminated by using the circuit shown in the figure (see formula 2), variations in resistance value (RA acid component) remain.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a constant current circuit with less variation in supplied current.

[Structure of the Invention] (Means for Solving the Problems) The present invention connects the collector to a first potential point via a load circuit, and connects the emitter to a second potential point via a first resistor. a first circuit having a connected one-herald transistor; a second resistor having one end connected to the first potential point; and a second resistor having one end connected to the first potential point;
includes a series connection with a third resistor whose value is smaller than that of the second resistor; a second circuit that supplies a voltage proportional to the voltage determined by a third resistance ratio to the base of the transistor, and circuit elements other than the second resistor are configured on the same semiconductor integrated circuit, The device is characterized in that the second resistor is a resistor provided outside the integrated circuit.

(Function) In general, in integrated circuits, the values of the resistors themselves vary widely, but the ratio between the resistors can be considered to be approximately constant t. Furthermore, by selecting a resistor to be used externally, the resistance value can be made highly accurate and have a low temperature coefficient.

In the case of the present invention, the constant current supplied to the load circuit is determined by the first resistor, the second resistor, and the third resistor, and the second resistor is made larger than the third resistor, and By configuring the second resistor with a resistor outside the integrated circuit, it is possible to eliminate variations in the current flowing through the load circuit.

(Example) The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a circuit diagram showing an embodiment of a constant current circuit according to the present invention.

In FIG. 1, reference numeral 1 indicates an external terminal of an integrated circuit that constitutes a constant current circuit according to this embodiment, and the portion to the left of the dotted line shows the internal configuration of the integrated circuit.

Transistor Q1 in the integrated circuit constitutes a constant current source,
The collector is connected to a voltage source VCC via a load circuit RL, and the emitter is connected to a reference potential point via a resistor R3. The transistor Q2 has a collector connected to a reference potential point, an emitter connected to a voltage source VCC via a resistor R1, and a base connected to a resistor R.
It is connected to the reference potential point via 2 and also to the external terminal 1. Furthermore, the external terminal 1 is connected to a voltage source VCC via a resistor RO external to the integrated circuit.

In the constant current circuit having such a configuration, the current I can be expressed as in equation (4).

When the above equation (4) is transformed, the following is obtained. Here, if we set R2/RO<1, (
5) The formula becomes. R2 and R3 are resistors in the integrated circuit, and there is a large variation, but the amount and polarity of the variation are determined by each resistor R2.
, R3 have the same variation. Therefore, the ratio R2/R3 of both resistances has no variation and has a temperature coefficient of O.

For example, a lifting platform with the same value for each resistor R3 and R2,
Even if there are variations in both resistance values, the ratio R2 is approximately 1 and constant.

This eliminates the proportional term due to R3 and R2, and the variation factor of the current (2) depends only on the external resistance RO. On the other hand, since the external resistor RO can be selected to have good resistance value accuracy and temperature coefficient, it can be seen that as a result, the variation in current I can be reduced proportionally by increasing the precision of the resistor RO. Ru. In this way, the present invention provides a constant current circuit with little variation in the output current even if there is variation in each element.

FIG. 2 shows an embodiment of the present invention, and the same operation as in FIG. 1 is indicated by the same symbol 8.

That is, in this embodiment, the polarity of the transistor is reversed from that of the embodiment shown in FIG. R[, voltage source VCC
A resistor R3 is connected between this and the emitter. A transistor Q4 corresponding to the transistor Q2 has a collector connected to the voltage source VCC instead of P N I) to N I) N.
The emitter is connected to the base of the transistor Q3, and is also connected to the reference potential point via the resistor R1. Also, a resistor R2 in series with the external resistor RO
is connected between voltage source Vcc and the base of transistor Q4.

The operation of such a circuit is the same as that of the circuit in Figure 1 except for the polarity, so a detailed explanation will be omitted, but as in Figure 1, the variation in constant current I is caused by the external resistance. Determined by accuracy.

FIG. 3 shows a plurality of (n) transistors Q1-1 and Ql-2 corresponding to the transistor Q1 in the embodiment shown in FIG.
,...Q1-n are provided. That is, the bases of each transistor Q1-1, Ql-2, .
3-1, R3-2, and -R3-n are connected, and load circuits RL-1, Rl-2, and -Rl-n are connected to the collectors, respectively.

Such a circuit includes each load circuit RL-1, l-? L-2
.

. . . Constant current supplied to RL-n 11. I2...ln
It is possible to give each field equally or to have different fields.

In each embodiment, the use of a variable resistor as the external resistor RO has the advantage that the constant current can be varied while maintaining the temperature coefficient O.

[Effects of the Invention] As explained above, according to the present invention, even if there are variations in the individual elements inside the integrated circuit, the current can be supplied at a predetermined value without being affected by the variation, and a constant value with little variation can be achieved. This realizes a current circuit. Another advantage is that the value of the constant current can be changed simply by adjusting the value of the external resistance.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a constant current circuit according to the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram showing still another embodiment of the present invention. FIG. 4 is a circuit diagram showing a conventional constant current circuit, and FIG. 5 is a circuit diagram showing another conventional example. 01~Q4, Ql-1, Ql-2, ・Ql-n-1
-Transistor, RO, R1-R3...Resistor, RL・
...Load circuit, VCC...Voltage source, ■...Constant current. Agent Patent Attorney Susumu Ito Figure 1 Figure 2 Figure 4 Figure 5

Claims (2)

[Claims] (1) a first circuit including a transistor whose collector is connected to a first potential point via a load circuit and whose emitter is connected to a second potential point via a first resistor; and the first potential a second resistor having one end connected to the point, and a third resistor having one end connected to the second potential point and having a smaller value than the second resistor;
, a second circuit that supplies a voltage proportional to the voltage determined by a third resistance ratio to the base of the transistor, and circuit elements other than the second resistor are provided outside the same semiconductor integrated circuit. A constant current circuit characterized by being configured with a resistor. (2) A patent claim characterized in that the first circuit is formed by arranging a plurality of series circuits of the load circuit, a transistor, and a first resistor in parallel between the first and second potential points. The constant current circuit according to the range 1 above.