JPS6097708A - Constant current circuit - Google Patents

Abstract

PURPOSE:To obtain a constant current circuit possible for selecting an optional and desired temperature coefficient and less in the fluctuation of a power supply voltage by combining two circuits where the temperature coefficient of flowing current has a positive and a negative value. CONSTITUTION:The emitter area of transistors (TR) Q1, Q2 and Q3 is manufactured identically, and that of a TRQ4 is manufactured (n) times that of them. Through the constitution shown in Fig., a current I2 is given as I2=(kT/qR2)ln (n) and on the other hand, a current I3 is expressed approximately as I3 VBE/R3. Since the voltage VBE has a negative temperature coefficient, the current I3 has a negative temperature coefficient. Thus, a constant current output I0=I2+I3 is the sum of currents of the positive and negative temperature coefficients and the temperature coefficient of the current I0 is set bipolar by setting optionally the ratio of the currents I2 and I3. Then the current I2 is independently of a voltage Vcc and the current I3 is affected very slightly of the current I1 depending on the voltage Vcc, then the effect of power supply voltage fluctuation is not almost caused.

Description

Detailed Description of the Invention ■Technical Field of the Invention The present invention relates to a constant current circuit, particularly a first circuit in which the temperature coefficient of flowing current is a negative value, and a second circuit in which the temperature coefficient of the flowing current is a positive value. It is configured to have

The present invention relates to a constant current circuit configured to have an arbitrary desired temperature coefficient and to be less affected by fluctuations in power supply voltage.

■Technical background and problems In constant current circuits installed in IC circuits, a configuration is used in which the base potential of a transistor is maintained at a predetermined level, and the temperature coefficient of the flowing current generally has a negative value. Become. Furthermore, it is susceptible to fluctuations in the power supply voltage that provides the pace potential.

0Objects and Structure of the InventionThe present invention aims to solve the above-mentioned problems.1The constant current circuit of the present invention has a first circuit connected in series between a power source and ground. a second transistor, and a transistor iz, y-4 connected in series between the output terminal and ground, the collector and the pace of the first transistor being commonly connected to the pace of the third transistor. , the collectors and bases of the second transistor and the fourth transistor are cross-connected, the emitter area of the fourth transistor is twice that of the second transistor, and a resistor is connected in series between the output terminal and ground. The fifth transistor has a base connected to the base of the third transistor, and the output terminal is a constant current source. This will be explained below with reference to the drawings.

0 Examples of the invention The figure shows the configuration of an embodiment of the present invention. In the figure, Ql.

Q2. Ql, Q4, and Qa each represent the first term in the present invention. 2nd, 3rd. A 41st fifth transistor.

In particular, transistor Q4 corresponds to the large saturation current transistor according to the present invention. In addition, ``+Ran Rs are respective resistances, Vcc is the power supply voltage, Io is the constant current r obtained in the present invention, Is is the current flowing through the first circuit according to the present invention w I2 is the current r flowing through the second circuit according to the present invention. Il represents the current flowing through the control circuit according to the present invention.

In the figure, transistors Ql, Q2 . Assume that the emitter area of Qa is the same and has the unit l, and the emitter area of the transistor Q4 is multiplied by l and has the unit l,
Furthermore, the current amplification factor of each transistor is made sufficiently large. In this case, considering the circuit passing through the transistor Q'+Q41 and the resistor HQ and the circuit passing through the transistor Q3°Q2, the following equation is established. That is.

From equation (1) above, is obtained.

Here, 1. The temperature coefficient of diffusion resistance in a normal monolithic IC is around +0.2 [%/C0], but (2)
Since the temperature coefficient of the numerator kT in the equation is larger than this, the current I2 passing through the second circuit according to the present invention has a positive temperature coefficient.

On the other hand, the electrician 3 passing through the first circuit according to the present invention is.

The above current I3 is approximately given by: Here, since the voltage VBI11 has a negative temperature coefficient,
The current I3 has a negative temperature coefficient.

From these facts, the current Io is given by Io = Is + l5 (5), so by appropriately selecting the ratio of the current generator 2 and the current generator 3, the temperature coefficient of the current Io can be expressed as
It can be arbitrarily set relatively easily in both positive and negative directions with zero as the intermediate point.

Also, from the second equation above, the value of current I2 is equal to power supply voltage Vcc
can be set regardless of Also electrician 3.

Although the base-emitter voltage VBK1 of the transistor Qz changes slightly with the current II depending on the power supply voltage VCC, the rate of change is small, so that the influence of the power supply voltage Vcc on the desired constant current Io to be obtained is small. For this reason, it becomes possible to obtain a stable constant current 1o.

■As explained in detail, according to the present invention, a constant current of 1o is to be obtained.
It is possible to arbitrarily select the temperature coefficient of , and it is almost unaffected by the power supply voltage Vcc of the constant current 1o.

[Brief explanation of drawings]

The figure shows the configuration of an embodiment of the present invention. In the figure, #Ql + Qa + Qs * Qs are transistors. Q4 is a Tr with four times the emitter area, Io is the constant current to be obtained, Ia is the current passing through the first circuit, I2 is the current passing through the second circuit, Il is the current passing through the control circuit, and VCC is the power supply voltage. Patent applicant Hiroshi Mori (1 other person), agent patent attorney of Fujitsu Ltd.

Claims (1)

[Claims] The first one is connected in series between the power supply and ground. a second transistor, and a third transistor connected in series between the output terminal and ground. Fourth
a transistor, the collector and base of the first transistor are commonly connected to the base of the third transistor, the collectors and bases of the second transistor and the fourth transistor are cross-connected, and a fourth The fifth transistor has an emitter area twice that of the second transistor, is connected in series with a resistor between the output terminal and ground, and has a base connected to the base of the third transistor. , the output end should be a constant current source.
-Characteristic constant current circuit.