JPS6223213A - Constant current circuit - Google Patents

Abstract

PURPOSE:To obtain a simple constant current circuit in an electronic circuit by amplifying a base-emitter voltage of an input transistor (TR) by an amplifier circuit and giving the result between the base and emitter of an output TR. CONSTITUTION:The amplification factor G of an amplifier circuit 9 is expressed in equation 1 and the amplification factor is stable. Relation of equations 1, 3 exist, where Ii is a collector current of an input TR 7, Vi is a base-emitter voltage, IO, VO are respectively the current and voltage of an output TR 8, (q) is an electronic charge of an electron, (k) is the Boltzmann's constant, T is absolute temperature, Iis, Ios are constants depending on the drive capability of the input TR 7 and the output TR 8 respectively, and the both can not be equal in the equations. In the equation 2, the current Ii is nearly equal to the input of constant current from a constant current source and regarded as a constant value, but since the variable T is included in the equation, the voltage Vi is subjected to the effect of temperature and not constant. Since the voltage VO is the result of amplifying the voltage Vi by an amplifier circuit 9, the current IO of a TR 8 is given in equation 4. The right side of the equation 4 is all constant and a constant current flows to a load 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a large current constant current circuit that can be easily obtained in an electronic circuit.

〔Traditional! X technique]

Figure 2 is a circuit diagram showing an example of a constant current circuit that can be easily obtained in a conventional electronic circuit, in which (1) is a constant voltage power supply with a potential v0°, (2) is grounding, and (3) is a resistance value. The upper one is a sufficiently large resistor, and (4) the load whose ri impedance is ZL. Since the conventional constant current circuit was constructed as described above, the current flowing through the resistor (3) and the load (4) is Since Rr is chosen to be large enough so that Rr=Voo/(Rr+zL) Rr)IZL+, it becomes Il VQQ/Rr(1), and with Voo and Rr being constant values, this conventional It can be seen that the circuit operates as a constant spiral current circuit.

[Problems to be Solved by the Invention] In the conventional simple constant current circuit as described above, Rr) IZL+, which is a condition for formula (1) to hold, must be satisfied. In other words, the problem is that the voltage V0° of the constant voltage power supply (1) is mostly applied to the resistor (3) and can only be used under conditions where it hardly applies to the negative * (4).

Fig. 3 is a circuit diagram showing an application circuit of a current mirror circuit, and the one of this invention described later is an improved version of this. (5) #i constant current source, (6) are surrounded by dotted lines. The current mirror circuit (7) is the input transistor of the current mirror circuit (6), and (8) is the output transistor of the current mirror circuit (6) with the same characteristics as the input transistor (7). The sign of the function is as shown in Figure 2. First, to explain the operation of the current mirror circuit (6), when an input current is passed from the point where the collector and base are commonly connected to the input transistor (7), the input current flows between the collector and emitter of the output transistor (8). An output current equal to the current flows.In other words, since the base-emitter voltages of both transistors (7) and (8) are equal, the collector-emitter currents are also equal, and compared to these, both base currents can be ignored. As far as possible, the input and output currents will be equal.Therefore, the third
In the circuit shown in the figure, the input current of the current mirror circuit (6) is given as the current of the constant current source (5), and the output current of the circuit (6) is passed through the load (4). 5) It works so that a constant current flows. Is the output transistor (8) and the input transistor (7) of the circuit in Fig. 3 similar to each other in that only the current capacity is larger? By using the transistor shown in Figure 2, it is possible to amplify the current in (b) path (6), and by using the circuit shown in Figure 2 with a relatively small current as the constant current source (5), the load ( 4) It appears that a large amount of constant current can be shunted. However, the story is not so simple because the base current of the transistor (8) cannot be ignored relative to the input current.

This invention was made as a companion to solve the problems of the conventional ones as described above.
The object of the present invention is to provide a constant current circuit that can supply a constant current that is not affected by temperature even when most of the voltage is applied.

[Means for Solving Problems J] The constant current circuit according to the present invention has a stable amplification factor, high input impedance, and low output impedance.・It provides an output voltage between emitters. A constant input current is applied between the collector-base common connection and the emitter of this input transistor, and a constant input current is applied between the collector-emitter of this output transistor.
is the output current.

[Effect]

In this invention (1), the amplifier circuit firstly prevents the input of a constant current from burdening the output transistor with a non-negligible base-emitter current; Second, as a characteristic of general transistors, there is a relationship in which the collector-emitter current is approximately proportional to the exponent magnification of the quotient obtained by removing the base-emitter voltage with absolute temperature, so the influence of temperature can be reduced. The voltage between the base and emitter of the input transistor that receives 2!i - is amplified by a constant f?8 and a half, and the output voltage is applied between the base and emitter of the output transistor. The output current is a constant magnification of the input constant current that is not affected by the current.

〔Example〕

FIG. 1 is a circuit diagram showing the Kazuo side of this invention, (9
] is an amplifier circuit with a stable amplification factor, high input impedance, and low output impedance. Difference w′J amplifier, (11) , (
12) is a resistor whose resistance value is R1 and R2, respectively, as a component of the amplifier circuit (9), and other symbols are the same as those in FIGS. 2 and 3.

Since this embodiment is constructed as described above, it operates as follows. First, the amplifier circuit (9) is one of the well-known operational amplifiers and has high input impedance and low output impedance, and its amplification factor is 'kG', G = (R1 + R2) / R2...・・・
(2), and therefore it can be seen that the amplification factor is stable. Next, set the collector-emitter current of the input transistor (7) as 1, set the base-emitter voltage as Vl, and set the similar current and voltage of the output transistor (8). ,V. , the amount of charge of electrons is q, the Boltzmann constant is k, and the absolute temperature is T, each transistor has the following relationship.

Engineering i = Engineering 18exp (qvi/(kT))...
...(3) Engineering. = Engineering. 8eXp(q”ν./(kT)
of ·········
(4) However, Xi8. I. 8 is a constant determined by the drive wJ capabilities of the input transistor (7) and the output transistor (8), respectively, and here it is shown that the two do not have to be equal. In equation (, J), T1 is approximately equal to the constant current input of the constant current source, and is considered to be a constant value, but the temperature T
It can be seen that, as mentioned earlier, the influence of temperature on Vi is not constant.

Ma again. Since Vl is amplified by the amplifier circuit (9), from equation (2), V□=GV1=V1(Rx+Rz)/Ih −
−・−・−・(5). Equations (3), (4), (5)
More ■. = Engineering. 8((engine i/l1s): * *((R1
+R2)/R2))... is given by (6). For example, ``Kaishihonmusei β'' was used to mean ``β of α'' east.

In other words, all the values on the right side of equation [6] are constant values, and it is clear that by appropriately selecting the six values on the right side, a constant current whose magnitude can be arbitrarily selected can be passed through load (4). .

Moreover, since the configuration as shown in FIG. 1 makes it possible to apply most of the voltage v0° of the constant voltage power supply (1) to the load (4), the above problem is solved.

[Effects of the Invention] As explained above, the present invention provides simple voltage regulation in the simulator circuit by amplifying the base-emitter voltage of the input transistor using an amplifier circuit and applying the amplified voltage between the base and emitter of the output transistor. This has the effect of providing a current circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of this invention, Fig. 2 is a conventional simple constant current circuit, and Fig. 3 is a circuit diagram showing an applied circuit of a conventional current mirror circuit, which is the basis of this invention. It is. In the figure, (7) is an input transistor, (8) is an output transistor, and (9) is an amplifier circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Amplification with a stable amplification factor, high input impedance, and low output impedance by inputting an input transistor to which a constant current is input between the common connection of the collector and base and the emitter, and inputting the voltage between the base and emitter of the input transistor. 1. A constant current circuit comprising: a circuit; and an output transistor to which an output voltage of the amplifier circuit is applied between a base and an emitter, and whose output current is a collector-emitter current.