JPH06282341A - Constant current circuit - Google Patents

Abstract

PURPOSE:To stabilize the output current of a constant current circuit to be frequently used for a semiconductor integrated circuit against fluctuation in a power supply. CONSTITUTION:When the base current of a transistor(TR) 2 is used as the starting current of a constant current source constituted of TRs 5, 6, 8, 10, 11 and resistors 4, 7, 9, the starting current can be reduced and fluctuation in the starting current due to the fluctuation of the power supply does not exert influece upon a current outputted from the collector of a TR 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current circuit used for semiconductor integrated circuits.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing an example of a conventional constant current circuit. In FIG. 5, reference numerals 5, 8, 10, 13 denote PNPs.
Transistors, 6, 11 are NPN transistors, 14 is a diode, 3, 4, 7, 9, 12 are resistors, and 1 is a power supply.

In this circuit, the starting circuit is the diode 1
4 and a resistor 3, when the power source 1 is connected, the anode current IA14 of the diode 14 becomes a starting current, the base current of the transistor 8 flows, and the transistor 8 is turned on. The constant current circuit is activated by the collector currents of the transistors 5 and 10 which have flowed to the emitter of 8 and have been turned on to the collectors of the transistors 6 and 11, respectively.

Here, the collector current I of the transistor 5
The ratio of C5 to the collector current IC10 of the transistor 10 is α, and the saturation currents of the transistors 6 and 11 are Is6 and
Assuming that IS11 and the resistance value of the resistor 7 are R7, the collector current IC5 of the transistor 5 is generally represented by (Equation 1). Here, q is the charge of the electron, k is the Boltzmann constant, and T is the absolute temperature.

[0005]

[Equation 1]

As is clear from (Equation 1), the collector current IC5 of the transistor 5 is a constant current that does not depend on the power supply 1, and therefore the current output from the collector of the transistor 13 that forms a current mirror with the transistor 5 is also constant. It becomes an electric current.

[0007]

In practice, however, the base potential of the transistor 5, the anode potential and the cathode potential of the diode 14 fluctuate as the power supply 1 fluctuates, so that the current flowing through the resistor 3, that is, the starting current fluctuates. Will end up. Here, the starting current is IA14, and IC5> IA
If 1n (IC5-IA14) ≈ 1n (IC5) from 14,
The collector current IC5 of the transistor 5 can be expressed as in (Equation 2).

[0008]

[Equation 2]

As is clear from this (Equation 2), in the conventional constant current circuit, the collector current of the transistor 5 also changes with the change of the power supply 1, and the current output from the collector of the transistor 13 does not become a constant current. There was a problem.

The present invention solves the above problems in the conventional constant current circuit, and an object of the present invention is to provide a constant current circuit in which the output current is not affected by the fluctuation of the power supply.

[0011]

The constant current circuit of the present invention comprises:
In contrast to the conventional constant current circuit that used the anode current of the diode as the starting current, the starting current is reduced by using the base current of the transistor.

[0012]

According to the structure of the present invention, the starting current can be made minute so that the influence of the fluctuation of the starting current due to the fluctuation of the power supply on the output current can be neglected, and the output current of the constant current circuit can be reduced. It is possible to make it insensitive to fluctuations in the power supply.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the constant current circuit of the present invention. In FIG. 1, reference numerals 5, 8, 10, 13 denote P.
NP transistors, 2, 6, 11 are NPN transistors, 3, 4, 7, 9, 12 are resistors, and 1 is a power source.

In this circuit, the starting circuit is composed of the transistor 2 and the resistor 3, and when the power source 1 is connected, the base current 1B2 of the transistor 2 becomes the starting current, and the constant current circuit is started as in the case of the conventional example of FIG. . Therefore, the collector current IC5 of the transistor 5 is the same as in (Equation 2) (Equation 3)
It is expressed as.

[0016]

[Equation 3]

If the base-emitter voltages of the transistors 5 and 8 are VBE5 and VBE8, respectively, and the resistance value of the resistor 4 is R4, the power supply voltage is VCC and the collector voltage VC5 of the transistor 5 is (Equation 4). It is represented by.

[0018]

[Equation 4]

Therefore, the base-emitter voltage of the transistor 2 is VBE2, the current amplification factor of the transistor 2 is hFE, the emitter current of the transistor 2 is IE2, and the resistor 3 is used.
When the resistance value of R3 is R3, the starting current, that is, the base current IB2 of the transistor 2 is as in (Equation 5).

[0020]

[Equation 5]

Further, in the circuit of the conventional example of FIG. 5, when the anode-cathode voltage of the diode 14 is VAC14, the starting current, that is, the anode current I of the diode 14 is obtained.
A14 becomes like (Equation 6).

[0022]

[Equation 6]

Therefore, assuming that VBE2≈VAC14, the relationship between the starting current IB2 of the constant current circuit of the embodiment of the present invention and the starting current IA14 of the conventional constant current circuit is as shown in (Equation 7).

[0024]

[Equation 7]

From (Equation 4), the collector voltage VC5 of the transistor 5 varies with the variation of the power supply 1, and (Equation 5),
From (Equation 6), the starting currents IB2 and IA14 vary, but from (Equation 7), the influence of the variation of the power supply 1 on the collector current IC5 of the transistor 5 represented by (Equation 2) and (Equation 3) is In the constant current circuit according to the embodiment of the present invention, the current output from the collector of the transistor 5 forming the current mirror with the transistor 5 is stabilized by about hFE times because the current is about 1 / hFE compared to the conventional constant current circuit. You can see that it is done.

Further, in the conventional constant current circuit, a method of increasing the value of the resistor 3 has been adopted in order to reduce the starting current, but the chip area becomes large when it is realized as a semiconductor integrated circuit. On the other hand, the constant current circuit of the embodiment of the present invention has an advantage that it is not necessary to increase the value of the resistor 3 and a stable output current can be obtained with a small chip area.

2, FIG. 3 and FIG. 4 are circuit diagrams showing other embodiments of the constant current circuit of the present invention. FIG. 2 shows the starting current by inserting a diode between the transistor 2 and the resistor 3. 3 that reduces the output current and stabilizes the output current, FIG. 3 that adds a transistor 15 and connects it to the transistor 2 in Darlington to reduce the starting current and stabilizes the output current, and FIG. 4 illustrates the resistor 15 The base voltage of the transistor 6 is stabilized with respect to the power supply and temperature by using the temperature characteristic of.

[0028]

As described above, according to the present invention, a constant current circuit which can minimize the starting current of the constant current circuit in a small chip area and can obtain a stable output current against fluctuations in the power supply is provided. realizable.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the constant current circuit of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the constant current circuit of the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the constant current circuit of the present invention.

FIG. 5 is a circuit diagram showing a conventional constant current circuit.

[Explanation of symbols]

 1 power supply 2,6,11,15 NPN transistor 3,4,7,9,12,16 resistor 5,8,10,13 PNP transistor 14 diode

Claims (4)

[Claims] 1. A collector of a first transistor is connected to a collector of a second transistor, the emitter of the first transistor is used as a power source via a first resistor, and the emitter of the second transistor is used as a second resistor. To the ground, the collector of the third transistor is connected to the collector and the base of the fourth transistor, the emitter of the third transistor is connected to the power supply via the third resistor, and the emitter of the fourth transistor is connected to the power supply. The emitter is connected to ground, the base of the first transistor is connected to the base of the third transistor, the base of the second transistor is connected to the base of the fourth transistor, and the emitter of the fifth transistor is connected to the base of the third transistor. Connect the base of the first transistor, the collector to ground, and the base to the collector of the first transistor. A constant current circuit in which the collector of the sixth transistor is connected to the power supply, the emitter is connected to the ground through the fourth resistor, and the base is connected to the collector of the first transistor. 2. The constant current circuit according to claim 1, wherein one or more diodes are inserted between the emitter of the sixth transistor and the fourth resistor. 3. The base of the sixth transistor is connected to the base of the seventh transistor, the collector of the seventh transistor is connected to the power supply, and the base is connected to the collector of the first transistor. The emitter of the seventh transistor. The fourth
The constant current circuit according to claim 1, wherein the constant current circuit is connected to the ground via the resistor. 4. The second resistor and the emitter of the fourth transistor are connected to ground via the fifth resistor.
Constant current circuit described in.