JPH04130906A - Constant current circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of current variation due to the hFE of a transistor(TR) by constituting a constant current circuit prevented from being influenced by the dispersion or the like of the VBE or hFE of the TR generated at the time of producing the TR. CONSTITUTION:When it is defined that current flowing into respective TRs Q1, Q2 is I4, the current ratio I1/I4 of respective current values I1, I4, the ratio IS4/IS1 of the saturation current IS4 of the TR Q4 to the saturation current IS1 of the TR Q1 and the ratio IS3/IS1 of the saturation current IS3 of a TR Q3 to the saturation current IS2 of the TR Q2 are respectively (n), the current I1 flowing into a resistor R3 is expressed by the shown expressions. When R4=R 2Vcc/R3(R1+R2) is formed, the expression I is expressed by the expression II. Since the current I1 flowing into the resistor R3 is determined by registers R1 to R3, the constant current circuit is not influenced by the hFE or VBE of respective TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant current circuit suitable for use in an integrated circuit.

[Conventional technology]

Conventionally, this type of constant current circuit is shown in Figures 3 and 4.
A circuit as shown in the figure is used.

In Figure 3, a resistor R5 connected between the power supply and ground
, R6 and the transistor Q2 set the potential at point C, and the resistor R7 sets the current at the input terminal 4 of the current mirror circuit 2.

In this circuit, the current (2) flowing through the resistor R7 is the power supply voltage vco, and the current flowing through the resistor R6 (2) is between R7 and R6.
The current ratio ■2/■ flowing in n is n, and the saturation current of Q is 5.
5. If the saturation current rsg of the Q tool is nRs, the following equation is obtained.

In the constant current circuit shown in Fig. 3, transistor Q2 (7)
Vsx (second term of equation (1)) and transistor Q joint hF
There is a problem that the electric current 2 varies depending on l: (third term). There is also a constant current circuit shown in FIG. 4 which eliminates the influence of vBE.

In this circuit, the current flowing through the resistor R3 is the current flowing through the transistors Ql and Q2, and the current ratio between ■ and ■3 is I! /Is,) The ratio of the saturation current Ll of the transistor Q1 to the saturation current IS4 of the transistor Q4 and the transistor Q
Current ratio I of saturation current IS2 of Q2 and saturation current IS3 of Q3
When s3/I S2 are each n, the following equation is obtained.

In the constant current circuit shown in FIG. 4, the influence of V, which was a problem in the constant current circuits shown in FIGS. 1 and 3, is eliminated.

[Problem to be solved by the invention]

In the conventional constant current circuit described above, in the case of the constant current circuit shown in Fig. 3, according to equation (1), variations in the VBE of the 0th turn of the transistor and the hFE of the transistor Qt- affect the current supplied to the Karen mirror circuit. As a result, the output current value actually used varies.

Also in the case of FIG. 4, the PNP transistor Ql
, Q4, NPN transistor Q2. Each V of Q3
Although the variations in BH can be canceled out, the equation (2
), the potential at point D is affected by the characteristics of the transistor due to the hFE of transistor QJ, and as in the case of FIG. 3, there is a problem in that the output current value of the current mirror circuit fluctuates.

An object of the present invention is to solve these problems and provide a constant current circuit in which fluctuations in the output current value are controlled.

[Means to solve the problem]

The configuration of the constant current circuit of the present invention is such that the base of the first transistor of the common collector type is connected to the common connection point of the first and second resistors connected in series between the first and second power supplies. ,
The emitter of this first transistor is connected to the emitter of a second transistor having conductivity opposite to that of this first transistor, and has a plurality of output terminals from a connection point where the base and collector of this second transistor are commonly connected. a first output terminal of the current mirror circuit and a base of a first third transistor having the same conductivity as the second transistor, the collector of the third transistor being connected to an input terminal of the current mirror circuit; The emitters of this third transistor are respectively connected to the emitters of a fourth transistor of the same conductivity as the first transistor;
A third resistor is connected between the collector of this fourth transistor and ground, a fourth resistor is connected between the base and collector of this fourth transistor, and the resistance of this fourth resistor is and the first and second parallel resistance values are approximately equal to the ratio of collector currents flowing through the first transistor and the fourth transistor.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

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

In this embodiment, resistors R1 to R and transistors Q1 to Q
A current mirror circuit 2 having a plurality of output terminals 3 is used.

The current flowing through resistor R3 is transistor Ql.

The current flowing through Q2 is calculated by the current ratio L/I.
A. Let n be the ratio IS4/IS of the saturation current of the transistor Q1, □ and the saturation current IS4 of the transistor Q4, and the ratio Is3/s2 of the saturation current 1s2 of the transistor Q2 and the saturation current IS3 of the transistor Q3, respectively.
It becomes as follows.

is the following formula.

Therefore, according to this circuit, the current flowing through the resistor R3,
is determined by the resistors R1, R2, and R3, and is not affected by hF, : or VBE of each transistor.

FIG. 2 is a circuit diagram showing another embodiment of the present invention, and the difference from FIG. 1 is that the transistors Q1 to Q+4 in FIG.
The structure is composed of transistors Qll to Q14 having conductivity opposite to that of the transistors, and has the same effect as in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to configure a constant current circuit that is not affected by variations in VBE and hFH due to transistor manufacturing and fluctuations in vl and hFE due to temperature changes, based on equation (4). is created, and the resistances R1 and R2
Even if the voltage is relatively large, there is an effect that the fluctuation of the current caused by the voltage of the transistor Q1 described above can be prevented.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of first and second embodiments of the present invention, and FIGS. 3 and 4 are circuit diagrams showing two sides of a conventional constant current source circuit. 1...Power supply terminal, 2...Current mirror circuit with multiple outputs, 3...Output terminal of current mirror circuit, 4...Current mirror circuit Input terminal, R1-R7... Resistor, Ql, Q4
．． Ql 2. Ql 3...PNP) transistor,
Q2. Q3. Ql 1゜Ql4...NPN) transistor, A, B, C, D... Connection point. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] The base of a common collector type first transistor is connected to the common connection point of the first and second resistors connected in series between the first and second power supplies, and the emitter of this first transistor is connected to the common connection point of the first and second resistors connected in series between the first and second power supplies. A first output terminal of a current mirror circuit that is connected to the emitter of a second transistor having conductivity opposite to that of the first transistor, and that has a plurality of output terminals from a connection point where the base and collector of the second transistor are commonly connected. and the base of a third transistor having the same conductivity as the second transistor, the collector of this third transistor being connected to the input terminal of the current mirror circuit, and the emitter of this third transistor being connected to the base of the third transistor having the same conductivity as the second transistor. A third resistor is connected between the collector of this fourth transistor and ground, and a third resistor is connected between the base and collector of this fourth transistor. A fourth resistor is connected to the fourth resistor, and the ratio of the resistance value of the fourth resistor to the parallel resistance values of the first and second transistors is set as the ratio between the first transistor and the fourth resistor.
A constant current circuit characterized in that the ratio of the collector current flowing through the transistor and the collector current is approximately equal to the ratio of the collector current flowing through the transistor.