JPH0620178Y2 - Constant current source circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a constant current source circuit configured by a current mirror circuit.

(Prior Art) An example of this type of constant current source circuit is shown in FIG. In the figure, PNP-type transistors 1 and 2 form a first current mirror circuit 3, NPN-type transistors 4 and 5 and a resistor 6 form a second current mirror circuit 7, and 8 and 9 indicate a first current mirror circuit 7. 3 to form the current mirror circuit 10. Start circuit 11 is N
It is composed of a PN-type starting transistor 12 and an FET 13 that functions as an equivalent resistance, and the base of the starting transistor 12 is connected to the common base of the first current mirror circuit 3. In the collector circuit of the transistor 9 of the third current mirror circuit 10, a load 1 that should supply a constant current
4 is connected, and the value of the current flowing therein is approximately equal to the sum of the emitter currents of the transistors 4 and 5, that is, twice the emitter current of the transistor 4. Here, ideally, the mirror ratio is 1, the collector currents of the transistors 1 and 2 are equal, and therefore the emitter currents of the transistors 4 and 5 are also equal to each other.

However, in the above configuration, when the power supply voltage Vcc ₁ changes, the collector currents of the transistors 1 and 2 do not become equal to each other, and the set current value flowing through the load 14 fluctuates. This is the power supply voltage VCC ₁
This is because the collector-emitter voltage VCE (1) of the transistor 1 changes due to the fluctuation of V.sub.1 and the collector current changes due to the Early effect even if the base current is constant. That is, in the constant current source circuit shown in FIG. 3, the collector-emitter voltage VCE of the transistor 2 is
Since (2) is short-circuited between the collector and the base, it is constant and equal to the base-emitter voltage VBE of the transistor 2 having a constant voltage characteristic, and does not fluctuate due to the power supply voltage VCC ₁ . On the other hand, the collector-emitter voltage CE (1) of the transistor ₁ is not determined by its own base-emitter voltage VBE, but is the sum of VCC1 to the base-emitter voltage VBE of the transistor 8 and the transistor 4. It will be the value subtracted. Therefore, the collector-emitter voltage VCE (1) of the transistor 1 is the power supply voltage VC
The collector ratio changes due to the Early effect, which changes depending on the size of C ₁ , and the mirror ratio deviates from 1. Conventionally, many methods have been attempted to solve such drawbacks, but in each case, the number of transistors is increased, which makes it difficult to form an integrated circuit, and the current consumption increases as the number of transistors increases. Had a drawback in that the number of transistors connected in series increased and it became difficult to drive at a low voltage.

(Problems to be Solved by the Invention) As described above, the conventional constant current source circuit has a drawback that the set current value fluctuates due to fluctuations in the power supply voltage, and an attempt to solve this has been made. Each of them had a problem that the number of transistors was significantly increased.

Therefore, an object of the present invention is to provide a constant current source circuit which can effectively prevent the setting current value in the current mirror circuit from changing due to the Early effect by adding one transistor or a number of transistors regarded as a single transistor. To provide.

[Structure of the Invention] (Means for Solving Problems) A constant current source circuit of the present invention is a first current mirror circuit in which each emitter of a main transistor and a slave transistor is connected to one of a pair of DC power supply terminals. And a main transistor and a sub-transistor having different emitter areas and a resistor connected between those emitters, collector currents are supplied from the sub-transistor and the main transistor of the first current mirror circuit to the collectors of the respective transistors. Second
Current mirror circuit and collector of output transistor
The emitter is connected between the emitter side of each transistor of the second current mirror circuit and the other DC power supply terminal, and the base of the load driving transistor is connected to the base of the output transistor. The third current mirror circuit, the collector of the starting transistor is connected to the one DC power supply terminal, the base is connected to the bases of the two transistors of the first current mirror circuit, and the emitter is connected to the other through an impedance element. A constant current source circuit comprising a starting circuit configured to be connected to the DC power supply terminal, and a compensation transistor is provided, and a main transistor of the second current mirror circuit is provided between an emitter and a collector of the compensation transistor. The collector and base of the transistor are connected in parallel, and the base of the compensating transistor is connected to the starting transistor. Those having features was constructed by connecting the emitter of Njisuta.

(Operation) Since the base and emitter of the main transistor of the first current mirror circuit are short-circuited, the collector-emitter voltage VCE
Is equal to the base-emitter voltage VBE having a constant voltage characteristic and is not affected by the power supply voltage. In addition, the collector-emitter voltage VCE of the slave transistor can be calculated from the sum of its own VBE and the startup transistor VBE.
Since it is equal to the value obtained by subtracting BE, the constant voltage characteristic of each VBE does not affect the power supply voltage. As a result, the collector-emitter voltage VCE of the main transistor and the sub-transistor is no longer dependent on the power supply voltage, so that the collector current and thus the set current value supplied to the load becomes constant.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. Reference numeral 21 denotes a first current mirror circuit, which has two PNs corresponding to a sub transistor and a main transistor, respectively.
The bases of the transistors 23, which are the main transistors, are configured by connecting the bases of the P-type transistors 22 and 23 in common and connecting the emitters to the first power supply line VCC ₁ ( _{one of a} pair of DC power supply terminals). -The collectors are short-circuited. A second current mirror circuit 24 has two NPN-type transistors 2 corresponding to a main transistor and a slave transistor whose bases are commonly connected.
5, 26 and a resistor 27, the collectors of the transistors 25 and 26 are connected to the collectors of the transistors 22 and 23 of the first current mirror circuit 21, and the transistors 25 and 26 are driven at the same current value. Has become. Note that the transistor 26 has a so-called double-emitter structure, and the emitter area thereof is the transistor 25.
It is twice as much as that. 28 is a third current mirror circuit, which also has two NPs as an output transistor and a load driving transistor whose bases are commonly connected.
The second current mirror circuit 24 is provided with N-type transistors 29 and 30, and the emitter of the transistor 25 and one end of the resistor 27 are connected to the collector of the transistor 29, and the emitter of the transistor 26 is connected to the other end of the resistor 27. ing. The collector and base of the transistor 29 are short-circuited, the emitter is grounded (connected to the other of the pair of DC power supply terminals), and the collector of the transistor 30 is connected to the second power supply via the load 31 to which a constant current is to be supplied. It is connected to line Vcc ₂ . On the other hand, 32 is a starting circuit, which is an NPN-type starting transistor 33.
And F whose gate is grounded to function as an equivalent resistance.
ET34 is provided, the collector of the starting transistor 33 is connected to the _first power supply line Vcc ₁ , the base is connected to the common base of the transistors 22 and 23 in the first current mirror circuit 21, and the emitter is the source / source of the FET 34. It is grounded through the drain. Also, 35 is P
An NP-type compensating transistor, the emitter of which is connected to the collector of the transistor 22, the collector of which is connected to the common base of the transistors 25 and 26 in the second current mirror circuit 24, and the base of which is the emitter of the starting transistor 33. It is connected to the.

In the above configuration, when a voltage is applied to the power supply lines Vcc ₁ and Vcc ₂ , a base current flows through the transistors 22 and 23 of the first current mirror circuit 21 through the base and emitter of the starting transistor 33. As a result, both the transistors 22 and 23 are turned on and the current mirror circuits 21, 24 and 28 are brought into the constant current operation state, and the load 3
The value of the current that flows in 1 is the transistor 25 and the transistor 2
It is maintained equal to the sum of the 6 emitter currents, ie twice the emitter current of the transistor 25. In this state, the collector-emitter voltage VCE (23) of the transistor 23 constituting the first current mirror circuit 21 is short-circuited between its base and collector.
Equal to the emitter-to-emitter voltage VBE (23), even if the power supply voltage VCC
Maintains a constant value that does not change even when ₁ fluctuates. On the other hand, the collector-emitter voltage VCE of the transistor 22 (22), only from VCC ₁ the sum of the collector potential and VBE (22) (referred to the base-emitter voltage of the transistor 22. Hereinafter the same) and VBE (33) It goes down and goes up by VBE (35), so each VB
If E is equal, then VBE. That is, the collector-emitter voltage VCE (22) of the transistor 22 also has a constant value of VBE that does not depend on the power supply voltage Vcc ₁ , and is equal to that of the transistor 23. Therefore, according to the above configuration, the collector-emitter voltage VCE of the transistors 22 and 23 maintains a constant value even if the power supply voltage Vcc ₁ varies, and due to the Early effect, each transistor 22,
It is possible to reliably prevent the collector currents of 23 from being different from each other, and it is possible to maintain the current value flowing through the load 31 at the set value regardless of the fluctuation of the power supply voltage Vcc ₁ . Moreover, since only one transistor (compensation transistor 35) is added, the circuit is simple and suitable for integration into a circuit, and the power consumption hardly increases. Since it is only higher than VBE by VBE, low voltage driving is possible.

FIG. 2 shows a different embodiment of the present invention. The difference from the above embodiment is that the transistor 36 for guaranteeing the current amplification factor is provided so as to be suitable for the case where a plurality of loads 31 are provided. . Since the other points are the same as those of the first embodiment, the same reference numerals are given to the same portions and detailed description thereof will be omitted.

[Effects of the Invention] As described above, the present invention is a constant voltage of the base-emitter voltage in the compensation transistor and the intrinsically provided start-up transistor only by adding the compensation transistor to the conventional circuit. It is possible to make the collector-emitter voltage of the slave transistor in the first current mirror circuit constant by utilizing the characteristics. As a result, even if there is a change in the power supply voltage, it is possible to suppress changes in the set current value supplied to the load, and since the number of elements hardly increases, power consumption is suppressed and low voltage driving is possible. It has a great effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional example. In the drawing, 21 is a first current mirror circuit, 22 is a transistor (sub-transistor), 23 is a transistor (main transistor), 24 is a second current mirror circuit, 25 is a transistor (main transistor), 26 is a transistor (sub-transistor). Transistor), 27 is a resistor, 28 is a third current mirror circuit, 29 is a transistor (output transistor), 3
Reference numeral 0 is a transistor (load driving transistor), 32 is a starting circuit, 33 is a starting transistor, and 35 is a compensating transistor.

Claims (1)

[Scope of utility model registration request] 1. A first transistor comprising emitters of a main transistor and a slave transistor connected to one of a pair of DC power supply terminals.
Current mirror circuit, a main transistor and a slave transistor having different emitter areas, and a resistor connected between those emitters, and a collector current from the slave transistor and the main transistor of the first current mirror circuit to the collector of each transistor. Is supplied between the second current mirror circuit and the collector-emitter of the output transistor.
Current mirror circuit connected between the emitter side of each transistor and the other DC power supply terminal and the base of the load driving transistor is connected to the base of the output transistor. And a collector of the starting transistor connected to the one DC power supply terminal, a base connected to the bases of two transistors of the first current mirror circuit, and an emitter connected to the other DC power supply terminal via an impedance element. In the constant current source circuit including a starting circuit configured as described above, a compensation transistor is provided, and the emitter and collector of the compensation transistor are provided between the collector and base of the main transistor of the second current mirror circuit. And the base of the compensation transistor is connected to the emitter of the starting transistor. Constant current source circuit, characterized by being configured to connect to.