JPS6097706A - Constant current drive circuit - Google Patents

Abstract

PURPOSE:To control the dependency of an output current on temperature by allowing a constant current source to generate a current proportional to the absolute temperature so as to compensate the temperature characteristic of a drive circuit. CONSTITUTION:A current IT is applied as a collector current of a transistor (TR) Q6, amplified by a current mirror circuit comprising TRs Q6, Q7 and Q8 and flows as a collector current of the TRQ1. The collector current of the TRQ2 is a current being a quotient of a base-emitter voltage VBE(Q1) of the TRQ1 divided by a resistor R1. The collector current of the TRQ3 flows as a sum of collector currents of the TRs Q1, Q2 and a voltage drop is caused by a resistor R2. Since the TRs Q3, Q4 constitute a current mirror circuit, an output current is extracted as the collector current of the TRQ4 corresponding to the voltage drop of the resistor R2. The control of temperature dependency of the output current is attained by making the current IT to a current proportional to the absolute temperature including the temperature coefficient of a voltage VBE(Q1) and the resistors R1, R2. Furthermore, this circuit has an advantage, where the current IT is amplified by the TRs Q6, Q7 and Q8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a constant current drive circuit that drives a load with a constant current.

[Prior art]

A conventional circuit of this type is shown in FIG. In Figure 1, IO is a constant current source, Ql to Q5 are NP
R1 represents an N-type transistor and a resistor. Power supply terminal Vc
A power supply is connected between c and the ground terminal GND, and the output terminal 0
A load is connected between the UTPtJT and the power supply terminal Vce.

Next, the operation of the conventional device will be explained. When the power is turned on, a current of IO flows from the constant current source IO to the transistor Q2.
further connected to resistor R1 and transistor Q
It flows into the base of transistor Q5, passes through the emitter from the base of transistor Q5, reaches the ground terminal GND via the bases of transistors Q3 and Q04, and the circuit starts operating. Then, negative feedback is applied by transistors Q2 and Ql, and as a result, the collector current of transistor Q2 becomes stable according to the following equation.

Here, Ic (Q2) represents the collector current of the transistor Q2, VBE (Ql) represents the base-emitter voltage of the transistor Ql, and R1 represents the resistance value of the resistor R1. Therefore, the collector current 1c (Q3) of transistor Q3 can be expressed by the following equation.

I c (Q3) = I o + I c (Q2)...
-(2) Here, R0 indicates the current value of the constant current source. That is, since the transistors Q3 and Q4 form a current mirror circuit by connecting their respective bases and emitters to each other, the output current 1c (Q4) can be expressed by the following equation.

I c (Q4) -1c (Q3) ... (3) That is, (11 (2) (from formula 31).

Since the conventional constant current drive circuit is configured as described above, even if IO is constant regardless of temperature, VBE (
Ql) has a temperature coefficient of approximately −'l m V/°C,
Furthermore, if R1 is also integrated circuit, approximately +2000ppm
/ ” Since it has a temperature coefficient of C, the output current 1c (Q
4) cannot be set to a constant value regardless of temperature.

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above, and it creates a constant current source by applying the potential difference between the base and emitter of two opposing transistors to both ends of a resistor. A constant current source that generates a current proportional to the absolute temperature is configured with a current proportional to the absolute temperature as a source, and a current that is dependent on the voltage between the base and emitter of the transistor is created, and the above two currents are converted into a current. Flow through the transistor of the mirror circuit and the resistor connected to its emitter, and cancel out the positive temperature coefficient of the potential difference between the base and emitter of the two opposing transistors and the negative temperature coefficient of the base-emitter voltage of the transistor. By simultaneously canceling out the temperature coefficient of the resistance when producing the above-mentioned constant current and the temperature coefficient of the resistance when producing the current dependent on the above-mentioned base-emitter voltage, the output current can be increased regardless of the temperature. It is an object of the present invention to provide a constant current drive circuit that can obtain a current having a desired temperature coefficient.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure! T is a constant current that generates a current proportional to absolute temperature, which is configured with a current proportional to absolute temperature created by applying the potential difference between the base and emitter of two opposing transistors across a resistor as a source. source,
Ql and Q8 are NPN transistors, and R1 and R2 are resistors whose structure is the same as that used to generate the current proportional to the absolute temperature. This is the second resistance. and the base of the first transistor Q1, the emitter of the second transistor Q2, the base of the fifth transistor Q5, and the first resistor R.
One terminal of the first resistor R1 is interconnected with the other end of the first resistor R1, the emitter of the first transistor Ql, and the third transistor Q.
The bases of the third transistor Q3, the base of the fourth transistor Q4, and the emitter of the fifth transistor Q5 are connected to each other, and the emitter of the third transistor Q3 and one terminal of the second resistor R2 are connected to each other. The other end of the second resistor R2 and the emitter of the fourth transistor Q4 are connected, and this connection point is set as a ground terminal GND,
The collector of the fourth transistor Q4 is the output terminal OUTP
UT, and the collector of the fifth transistor Q5 and the second
The collector of the transistor Q2, the collector of the seventh transistor Q7, the collector of the eighth transistor Q8, and one terminal of the constant current source IT are interconnected, and this connection point serves as the power supply terminal Vcc, and the emitter of the sixth transistor Q6 and the collector of the eighth transistor Q8 are interconnected. The emitter of the seventh transistor Q7 and the collector of the first transistor Ql are interconnected, and the sixth transistor Q6
The base of the seventh transistor Q7, the base of the second transistor Q2, and the emitter of the eighth transistor Q8 are interconnected, and the collector of the sixth transistor Q6, the base of the eighth transistor Q8, and the other terminal of the constant current source IT are interconnected. terminals are interconnected. In addition, a power supply is connected between the power supply terminal Vcc and the ground terminal GND, and the output terminal 0UT
A load is connected between PUT and power supply terminal Vce.

Next, the operation of the present invention will be explained using FIG. 2. When the power is turned on, a current IT flows from the constant current source IT from the base of the transistor Q8 to the emitter, is supplied to the base of the transistor Q2, passes through the emitter, flows from the base of the transistor Q5 to the emitter, and flows to the bases of the transistors Q3 and Q4. A current is supplied from the emitter of transistor Q3 through resistor R2 or from the emitter of transistor Q3 to
4 and reach the ground terminal GND, respectively, and the circuit starts operating. Then, transistor Q2
and Q6. Q8. Negative feedback is applied via Q7 and Ql, and as a result, the collector current of transistor Q2 becomes stable according to the following equation.

1 (1 Here, Ic (Q2) is a transistor.2's collector current, VBE (Ql) is a transistor.2's base-emitter voltage, and R1 is the resistance value of the resistor R1.

Also, at this time, a transistor. 1 collector current 1c (
Ql) is a transistor. 6. Q7. A current IT from a constant current source IT that generates a current proportional to the absolute temperature amplified with a constant gain by a current mirror circuit constituted by Q8, that is, a transistor of the current mirror circuit. 6 and Q7 (7) When the base-emitter junction area ratio is n, the flow is as n I T, so it can be expressed by the following equation.

I c (Ql) -n ・IT -(63 where JT
represents the current value from a constant current source that generates a current proportional to absolute temperature, and this constant current source is created by applying the potential difference between the base and emitter of two opposing transistors to both ends of a resistor. Since it is a constant current source that generates a current proportional to absolute temperature, the current value can be expressed by the following equation.

Here, ΔVBE represents the potential difference between the base and emitter of two opposing transistors, and R represents the resistance value of a resistor having the same structure as resistors R1 and R2.

Therefore, the collector current 1c (Q3) of the transistor Q3 can be expressed by the following equation from (5), (6), and (7).

I c (Q3) = I c (Ql) + I c (
Q2) .=T81 Next, this current 1c (Q3) is converted into a voltage by the resistor R2, and its value can be expressed by the following equation.

VR2=R2・Ic(Q3)・al... (1
1) Here, VH2 is the voltage drop across resistor R2, and R2 is the voltage drop across resistor R2.
The resistance value of 2 is shown.

Next, we can transform equation (11) and write it as follows.

・VBE(Ql)...(12) Here, ΔV[lE can be expressed by the following equation.

Here, q represents the electron charge, k represents the Boltzmann constant, T represents the absolute temperature, and Jl and J2 represent the current densities of the two opposing transistors.

Further, VBE (Ql) can be expressed by the following equation.

VBE (Q 1 ) = Vgo (1--)O + VBEO(-) ... (14) O where Vgo is the extrapolated voltage of the energy band gap determined by the semiconductor material at the absolute temperature T = 0°K and also V Bl! 0 also indicates the base-emitter voltage under the same conditions.

Therefore, by substituting equations (13) and (14) into equation (12), we get ... (15), and in order to calculate the temperature coefficient, equation (I5) can be changed to the absolute temperature T
Differentiating with , we get the following.

aT Rq J2 Therefore, in order to set the temperature coefficient to 0, if the right side = 0, the following condition can be derived.

...(17n) If this is set as To-T, the equation (17) becomes as follows.

Vg=VT+VBE (Ql) ・= (19), and if silicon is chosen as the semiconductor material, Vg=1°24 (V)
Therefore, from equation (19), transistor Q3(7)IL/
Since it is sufficient to set the current 1c (Q3) to the ratio of VT and VBE (Ql), the following equation holds true.

...(20) (K is a constant) That is, it becomes. Here, Ic (Q2) represents the collector current of transistor Q2, and Ic (Ql) represents the collector current of transistor Q1. In other words, as shown in the following equation, Ic (Q2) and Ic
(Ql), the output current 1c (Q4) can be taken out as a constant current independent of temperature.

VBE (Ql) I c (Q2) Vg-VBI! (Ql) I c (Ql)...
(22) In short, IT in Figure 2 is a current proportional to the absolute temperature including the temperature coefficient of resistance, and this current is
Assuming that the DC current amplification factor hFE of Q1 to Q8 is sufficiently large, it is supplied as the collector current of transistor Q6. Here, transistor Q6. Q7. Since QB constitutes a current mirror circuit, transistor Q
6 and the base-emitter junction area of Ql, and flows as the collector current of transistor Q1.

On the other hand, negative feedback is applied by transistors Ql and Q2 and resistor R1, and the collector current of transistor Q2 is determined by the value obtained by dividing the base-emitter voltage of transistor Q1 by resistor R1. Of course, the temperature coefficient of resistor R1 is It flows through resistor R1 with a temperature coefficient of the base-emitter voltage of transistor Q1.

In this way, a current proportional to the absolute temperature flows as the collector current of transistor Q1, and also flows as the collector current of transistor Q1.
A current obtained by dividing a base-emitter voltage of 1, that is, a voltage with a negative temperature coefficient by resistor R1, flows through resistor R1, and the above two types of current are supplied to the collector of transistor Q3, where The combined current flows as a collector current of transistor Q3, and is converted from current to voltage by resistor R2. This voltage drop across the resistor R2 cancels out the temperature coefficients of all the resistors, and at the same time can be obtained as a constant voltage unrelated to changes in the ambient temperature if the conditions of equation (22) are set.

Here, since the bases of transistors Q3 and Q4 are connected to each other to form a current mirror circuit, the collector current of transistor Q4 is obtained as a constant current independent of changes in ambient temperature.

It is also possible to deliberately shift the relationship in equation (22) to intentionally give a positive or negative temperature coefficient.

In this way, in this embodiment, not only can the dependence of output current on temperature be controlled, but also a large output current can be obtained from a constant current source with a smaller current value than in the conventional constant current drive circuit.

Note that in the above embodiment, the constant current drive circuit is “ON”.
Another embodiment of the present invention is shown in FIG. 3, in which a control input for turning the switch OFF is added. Here, C0NT is a control input terminal, and R3 is an impedance lowering resistor inserted to stabilize the current mirror circuit.

[Effects of the Invention] As described above, according to the present invention, a constant current source is proportional to the absolute temperature created by applying the potential difference between the base and emitter of two opposing transistors to both ends of a resistor. A constant current source that generates a current proportional to the absolute temperature is configured using the current as the source, and further generates a current that depends on the base-emitter voltage of the transistor.
A current is passed through the transistor of the current mirror circuit and the resistor connected to its emitter, and the positive temperature coefficient of the potential difference between the base and emitter of the two opposing transistors and the negative temperature coefficient of the voltage between the base and emitter of the transistor are determined. to cancel each other out, and at the same time, the temperature coefficient of the resistance and the base temperature when creating the above constant current.
By simultaneously canceling the temperature coefficient of resistance when creating a current that depends on the emitter voltage, it is possible to not only control the temperature dependence of the output current, but also to
This has the effect that a large output current can be obtained from a constant current source with a smaller current value than a conventional constant current drive circuit.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional constant current drive circuit, Figure 2 is a circuit diagram showing a conventional constant current drive circuit.
FIG. 3 is a circuit diagram showing a constant current drive circuit according to one embodiment of the invention, and FIG. 3 is a circuit diagram showing a constant current drive circuit according to another embodiment of the invention. IT... Constant current source, Ql-Q8... 1st to 8th
transistors, R1, R2...first. second resistance,
VCC...power supply terminal, GND...ground terminal, 0UT
PUT...Output terminal. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] (11) A constant current that generates a current proportional to the absolute temperature, which is configured with a current proportional to the absolute temperature created by applying the potential difference between the base and emitter of two opposing transistors across the resistor as a source. The base of the first transistor, the emitter of the second transistor, and the second resistor have the same structure as the resistor. 5 interconnecting the bases of the transistors and one terminal of the first resistor, interconnecting the other end of the first resistor, the emitter of the first transistor, and the collector of the third transistor;
interconnecting the base of the third transistor, the base of the fourth transistor, and the emitter of the fifth transistor, and connecting the emitter of the third transistor and one terminal of the second resistor;
The other end of the second resistor and the emitter of the fourth transistor are connected, and this connection point is used as a ground terminal, the collector of the fourth transistor is used as an output terminal, and the collector of the fifth transistor, the collector of the second transistor, and the collector of the seventh transistor are connected. The collector, the collector of the eighth transistor, and one terminal of the constant current source are interconnected, and this connection point is used as a power supply terminal, and the emitter of the sixth transistor, the emitter of the seventh transistor, and the collector of the first transistor are interconnected. The base of the sixth transistor, the base of the seventh transistor, and the second
The base of the transistor and the emitter of the eighth transistor are interconnected, and the collector of the sixth transistor, the base of the eighth transistor, and the other terminal of the constant current source are interconnected, and the power supply terminal and the ground terminal A power supply is connected between the output terminal and the power supply terminal, or a load is connected between the output terminal and another power supply to control the current flowing through the load to the desired temperature. A constant current drive circuit characterized in that the current value is set to have a characteristic.