JP2002149248A - Constant-current circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant-current circuit which is so constituted that a mirror current flowing to a current mirror circuit is made constant irrelevantly to temperature variation. SOLUTION: The circuit comprises a current mirror circuit which has (n) transistors, the constant-current circuit which makes constant the mirror current flowing to the current mirror circuit, and a transistor for temperature correction which has its emitter connected to the constant-current circuit through a resistance. At high temperature, the transistor for temperature correction increases the current flowing to the emitter of a first transistor for a constant current through the mentioned high resistance and decreases the emitter potential of the 1st transistor, thereby suppressing an increase of the current flowing to the current mirror circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a constant current circuit suitable for audio equipment such as a car stereo.

[0002]

2. Description of the Related Art In audio equipment such as a car stereo, it is necessary to supply a constant current to each circuit. Therefore, a 1: n current mirror type constant current circuit is used.

FIG. 3 shows a conventional current mirror type constant current circuit. Reference numerals 1, 2, 3, 4... N denote first, second and third transistors for a current mirror constituting a current mirror circuit. A fourth transistor and an n-th transistor, wherein the base and the collector of the first transistor for current mirror 1 are coupled and the emitter is a power supply V;
Connected to cc.

The collector and base of the first transistor 1 for current mirror are connected to the second transistor 2 for current mirror, the third transistor 3 for current mirror, the fourth transistor 4 for current mirror, and the n-th current mirror. The bases of the transistors are connected, and the emitters of the second transistor for current mirror 2, the third transistor for current mirror 3, the fourth transistor for current mirror 4, and the n-th transistor for current mirror are connected to a power supply Vcc, respectively. I have.

Reference numeral 5 denotes a starting transistor, and reference numerals 6 and 7 denote a first constant current transistor and a second constant current transistor constituting a constant current circuit. The collector of the first constant current transistor 6 is the first current mirror first transistor. Connected to the collector of transistor 1, the emitter of the constant current transistor 6 is grounded via a resistor 8, the base and collector of the second constant current transistor 7 are connected, It is connected to the base and to the collector of the current mirror second transistor 2.

In the above, the current I ₀ flowing between the emitter and the collector of the current mirror second transistor 2 of the current mirror circuit is obtained by I _{0 =} kT / q · En · n / R. Where k: Boltzmal constant, q: electron charge, and T: absolute temperature.

As shown in FIG. 4, in a car audio, the temperature inside the car may change from -40.degree. C. to 125.degree. When a change in the constant current source is observed with respect to the temperature change, a difference of about 15 μA occurs.

[0008]

In the above-described current mirror circuit, the ratio of 1: n (n is the number of transistors forming the current mirror) suppresses the Early effect, and the constant current source changes with temperature. Is reduced. However, it is necessary to keep the temperature constant even in a wide range of temperature change, but in practice, as described above, a change in the constant current source occurs particularly at a high temperature.

[0009]

SUMMARY OF THE INVENTION The present invention provides a 1: n (n is the number of transistors constituting a current mirror) current mirror circuit, a constant current circuit for supplying a constant current to the current mirror circuit, An object of the present invention is to provide a constant current circuit which comprises an operating temperature correction circuit and suppresses a change in the constant current circuit in the temperature correction circuit at a high temperature.

Further, the present invention provides a current mirror circuit having a first transistor for a current mirror having a base and a collector coupled thereto, and n transistors having a base connected to the collector / base of the first transistor.
The collector of the first transistor of the current mirror circuit is connected to the collector and the emitter is grounded via a resistor. The first transistor for constant current and the base / collector are connected to the base of the first transistor for constant current. A constant current circuit having a second constant current transistor connected to the collector of the second transistor for mirror, a bias voltage that varies according to temperature is applied to the base, and the emitter is connected to the second constant current transistor via a high resistance. A temperature compensating circuit having a temperature compensating transistor connected to one transistor, and increasing a current flowing from the temperature compensating transistor to the emitter of the constant current first transistor through the high resistance from the temperature compensating transistor at a high temperature; A mirror that lowers the potential of the emitter of the first transistor for constant current and flows through the current mirror circuit Suppressing an increase in current is intended to provide a constant current circuit.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A constant current circuit according to the present invention will be described with reference to the drawings. The same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, reference numerals 1, 2, 3, 4,..., N designate a first transistor, a second transistor, a third transistor, and a fourth transistor for a current mirror constituting a current mirror circuit.
In the transistor and the n-th transistor, the base and the collector of the current mirror first transistor 1 are coupled, and the emitter is connected to the power supply Vcc.

The collector and base of the first transistor 1 for current mirror are connected to the second transistor 2 for current mirror, the third transistor 3 for current mirror, the fourth transistor 4 for current mirror, and the n-th current mirror. The bases of the transistors are connected, and the emitters of the second transistor for current mirror 2, the third transistor for current mirror 3, the fourth transistor for current mirror 4, and the n-th transistor for current mirror are connected to a power supply Vcc, respectively. I have.

Reference numeral 5 denotes a starting transistor, and reference numerals 6 and 7 denote a first constant current transistor and a second constant current transistor constituting a constant current circuit. The collector of the first constant current transistor 6 is the first current mirror first transistor. The collector of the transistor 1 is connected, the n emitters are grounded via the resistor 8, the base and the collector of the second constant current transistor 7 are connected, and are connected to the base of the first constant current transistor 6. And is connected to the collector of the current mirror second transistor 2.

Reference numeral 10 denotes a temperature correction circuit, a correction first transistor 12 whose base is connected to the power supply Vcc and whose collector is grounded via a resistor 11, and a correction circuit whose base is connected to the collector of the transistor 12. And the second transistor 13. The base of the first transistor 13 for correction is connected to the bases of the first transistor 1, the second transistor 2, the third transistor 3, the fourth transistor 4, and the n-th transistor for current mirror. The collector of the second transistor for correction 13 is connected to the power supply Vcc, and the emitter is connected to the emitter of the first transistor for constant voltage 6 via the resistor. The resistor 14 using the high-resistance, so that no large changes with respect to the change in the V _B of the correction for the first transistor 13.

The operation will now be described.
Is applied, a current flows through the first transistor 1 for the current mirror, and a bias voltage is applied to the base of the starting transistor 5 to turn it on. As a result, the same current flows through the second, third,..., N-th transistors 2, 3,.

The collector and base of the second constant voltage transistor 7 are short-circuited and diode-connected, and the base-emitter voltage of the first constant voltage transistor 6 is constant. The current flowing through the emitter / collector of the first constant voltage transistor 1 is constant. Therefore, the current flowing through the emitter / collector of the current mirror first transistor 1 is also constant, and the current mirror second and third current mirrors having a current mirror relationship therewith are also provided.
... the same constant current flows through the n-th transistor.

In the above description, the current I ₀ flowing between the emitter and the collector of the current mirror second transistor 2 of the current mirror circuit is I _{0 =} kT / q · En · n / R. Here, k: Boltzmal constant q: Charge of electrons T: Absolute temperature By setting the potential at the point B of the temperature correction circuit 10 to 0.7 V or more at room temperature, the second correction transistor 13 is turned on. Setting. At a low temperature, the V _B of the second correction transistor 13 tends to increase with a change of −2 mV / ° C. At this time, the current flowing from the emitter of the second correction transistor 13 to the resistor 14 becomes small, and the current flowing into the emitter of the first constant voltage transistor 6 becomes smaller as the temperature becomes lower.

Conversely, at high temperatures, the second correction transistor 1
3 of V _B becomes smaller direction. Accordingly, at this time, the current flowing from the emitter of the second transistor 13 for correction to the resistor 14 becomes large, and the first transistor 6 for constant voltage
The current flowing into the emitter of the first transistor 6 for constant voltage increases as the temperature increases, and the current flowing into the emitter of the first transistor 6 for constant voltage increases.

As shown in FIG. 2, as the current flowing into the emitter of the first constant voltage transistor 6 increases as the temperature increases, the emitter voltage of the first constant voltage transistor 6 decreases, and the constant voltage decreases. The current flowing through the collector / emitter of the first transistor 6 is suppressed so that the mirror current flowing through the first transistor 1, the second transistor 2, the third transistor 3, the fourth transistor 4, and the n-th transistor for the current mirror is reduced by -40. ℃ -1
A change of about 15 μA at a change of 25 ° C. is suppressed to a change of 2 μA.

[0021]

According to the present invention, a temperature compensating circuit which operates at a high temperature is provided, and a change in the constant current circuit is suppressed by the temperature compensating circuit at a high temperature. It can be suppressed and kept constant.

Further, the emitter of the temperature correction second transistor, to which a bias voltage that changes in accordance with temperature is applied to the base, is connected to the constant current first transistor via a high resistance. The current flowing to the emitter of the first transistor for constant current is increased through the high resistance, the potential of the emitter of the first transistor for constant current is reduced, the increase in the current flowing to the current mirror circuit is suppressed, and the temperature changes. However, the change in the current flowing through the current mirror circuit can be almost suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a constant voltage circuit according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between current and temperature of the constant voltage circuit of the present invention.

FIG. 3 is a circuit diagram of a conventional constant voltage circuit.

FIG. 4 is a characteristic diagram showing a relationship between current and temperature of a conventional constant voltage circuit.

[Explanation of symbols]

 Reference Signs List 1 first transistor for current mirror 2 second transistor for current mirror 3 third transistor for current mirror 4 fourth transistor for current mirror 5 starting transistor 6 first transistor for constant current 7 second transistor for constant current 10 temperature correction circuit 12 First transistor for correction 13 Second transistor for correction 14 Resistance

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (2)

[Claims] 1. A 1: n (n is the number of transistors constituting a current mirror) current mirror circuit, a constant current circuit that supplies a constant current to the current mirror circuit, and a temperature correction circuit that operates at a high temperature. A constant current circuit wherein the temperature correction circuit corrects a change in the constant current circuit at a high temperature to suppress an increase in a mirror current. 2. A current mirror circuit comprising: a first transistor for a current mirror having a base and a collector coupled to each other; and n transistors having a base connected to the collector and base of the first transistor; A first transistor for a constant current having a collector connected to the collector and an emitter grounded via a resistor, and a base / collector connected to the base of the first transistor for a constant current and a current mirror for the current mirror; A constant current circuit having a second constant current transistor connected to the collector of the second transistor; a bias voltage that varies according to temperature is applied to a base; A temperature compensating circuit having a temperature compensating transistor connected to the Sometimes, the current flowing from the transistor for temperature correction to the emitter of the first transistor for constant current through the high resistance is increased, the potential of the emitter of the first transistor for constant current is lowered, and the mirror current flowing to the current mirror circuit is reduced. A constant current circuit characterized by suppressing an increase.