JPS62165224A - Constant current circuit - Google Patents

Abstract

PURPOSE:To freely set a temperature coefficient in a specific range and to make the range of a usable supply voltage independent of the temperature coefficient to be set selectively by selecting a resistance ratio of the first resistance to the second resistance. CONSTITUTION:When the first resistance R1 is connected between emitters of the first and second NPN transistors TRs Q3 and Q4 and the second resistance R2 is connected between emitters of the second and third NPN TR Q4 and Q5 and the emitter of the second NPN TR Q4 is led out as an output terminal TOUT, an output current IOUT is given in accordance with a formula I. If temperature coefficients of resistances are not taken into consideration, the first term of the formula I is proportional to VBE and is about -3000 ppm/ deg.C negative temperature coefficient, and the second term is proportional to an absolute temperature T and is about +3000 ppm/ deg.C positive temperature coefficient. Consequently, the temperature coefficient is set freely in the range of -3000-+3000 ppm/ deg.C by selecting the resistance ratio of the first resistance R1 to the second resistance R2. Thus, the temperature coefficient is selected freely in the wide range and the range of the usable supply voltage is made approximately independent of the set temperature coefficient.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a constant current circuit, and more specifically, to an improvement of a constant current circuit that allows the temperature coefficient to be changed over a wide range by selecting a resistance value. This is related to.

[Conventional technology]

FIG. 3 shows the configuration of a conventional constant current circuit of this type.

That is, in this circuit of FIG. 3, Ql is the collector
First PN with base connected and emitter connected to power supply
P transistor, Q2 is a second PNP transistor with its base connected to the base of the first PNP transistor Q1 and its emitter connected to the power supply; Q3 is a first NPN transistor with its collector connected to the collector of the first PNP transistor Q1. transistor, Q4 has its collector connected to the second P
Q5 is a second NPN transistor connected to the collector of the first NPN transistor Q2 and its base connected to the base of the first NPN transistor Q3, and Q5 has its base connected to the collector of the second NPN transistor Q4 and its emitter connected to the second NPN transistor Q4. A third NPN transistor connected respectively to the base of NPN transistor Q4, and Q6 also connects collector-base and connects the collector to the third NPN transistor.
a third PNP transistor whose collector and emitter are respectively connected to the power supply of the NPN transistor Q5;
Q7 has its base connected to the base of the third PNP transistor Q6, its emitter connected to the power supply, and its collector connected to the output terminal T. 8. R1 is the first transistor connected between the emitters of the first and second NPN transistors Q3 and Q4, respectively.
The resistors R2 and R3 are second and third resistors connected between the emitters of the second and third NPN transistors Q4 and Q5, respectively, and grounded.

In this conventional circuit configuration, if the transistor sizes of transistors Q, Q2 are the same, and the emitter size of transistor Q3 is N times the emitter size of transistor Q4, then transistor Q
1. Since transistors Q2 constitute a current mirror circuit with a current ratio of l:1, transistors Q3. The collector current of Q4 is the same, and the following equation holds true.

Rr-AfhN ・・・・・・・・・(
1) E3-S Here"R3; Emitter current h of Q3; Poltzmann's constant T; Absolute temperature correction; electronic charge, and the voltage v2 seen across the resistor R is here, vBE4: of Q4. The pressure between base and emitter is 1i.

Also, transistor Q6. Q7 constitutes a current mirror circuit So-4, and therefore transistors Q8. Q7
Assuming that the transistor sizes of are the same, the output terminal T. 8
．． The resulting output current I. 8. is equal to the emitter current E5 of the transistor Q5 and is of first order.

Therefore, in this equation (5), if we do not take into account the temperature coefficient of resistance, the first term is proportional to vBE and has a negative temperature coefficient of approximately -3000PPl/''C; , the second term is proportional to the absolute temperature T and is approximately +30
It has a positive temperature coefficient of 00pp+m/''C.

In the constant current circuit with this conventional configuration, by selecting the resistance ratio of the first resistor R1 and the third resistor R3, the voltage can be increased from approximately 3000 ppm/"O to +3
The temperature coefficient can be freely set within the range of 000 ppm/'O.

[Problem that the invention seeks to solve]

However, in the case of the constant current circuit in the conventional example,
In addition to the disadvantage that the number of circuit components increases somewhat due to the circuit configuration, when trying to achieve a temperature coefficient close to +30009 pm/'0, for example, the resistance value of the third resistor used becomes large. Moreover, the voltage drop across the third resistor also increases, resulting in various impractical problems such as a narrowing of the usable power supply voltage range.

This invention was made to improve these problems in conventional circuits, and its purpose is to reduce the number of circuit components and to reduce the usable power supply voltage range to the temperature coefficient. The objective is to provide a constant current circuit of this type.

[Means for solving problems]

In order to achieve the above object, the present invention provides a first resistor between the emitters of each of the first and second NPN transistors, and a first resistor between each of the second and third NPN transistors in the circuit configuration of the conventional example. A second resistor is connected between the emitters, the problematic third resistor is omitted, and the emitter of the second NPN transistor is used as an output terminal.

[For production]

Therefore, in the case of this invention, the first resistor and the second resistor t
By selecting the resistance ratio between
The temperature coefficient can be freely set within the range of 00ppm/'C to +3000ppm/'C (7), and the usable power supply voltage range can be made almost unrelated to the selected temperature coefficient. By omitting the resistor, the circuit itself can be constructed relatively easily.

〔Example〕

Below, the first embodiment of the constant current circuit according to the present invention will be described.
This will be explained in detail with reference to the figures and FIG.

FIG. 1 shows a circuit configuration according to an embodiment of the present invention, and in this embodiment circuit of FIG. 1, the same reference numerals as in the conventional circuit of FIG. 3 indicate the same or corresponding parts.

In this embodiment circuit of FIG. 1, in the conventional circuit, the collector of the third NPN transistor Q5 is directly connected to the power supply, and the collector of the third NPN transistor Q5 is directly connected to the power supply.
03. of NPN transistor. Q, the first resistor R1 is connected between the emitters of each of the resistors R1, and the second and third resistors
NPN transistor Q4. The second resistor R2 is connected between the respective emitters of Q5, and the third
The resistor R3 is omitted, and the emitter of the second NPN transistor Q4 is used as the output terminal "OUT".

Here, also in this embodiment circuit of FIG. 1, the transistor Q1. The transistor sizes of Q, , are the same, and the emitter size of transistor Q3 is the same as that of transistor Q4.
If it is N times the emitter size of the transistor Q, the emitter current IE3 of the transistor Q and the emitter current IE4 of the transistor Q are, as in the case of the conventional circuit, I = I - N... (6) R3
R4-R1-3, and the emitter current of transistor Q5 E5 is, therefore, the output current I. UT becomes .

However, in this equation (8), if we do not take into account the temperature coefficient of resistance, the first term is proportional to vBH and has a negative temperature coefficient of about -3000 ppm/"C! , on the other hand, the second term is proportional to the absolute temperature T and is approximately +3
It has a positive temperature coefficient of 0QQppm/'O.

In the case of a constant current circuit based on the configuration of the embodiment shown in FIG. 1, by selecting the resistance ratio of the first resistor R1 and the second resistor R2, the circuit configuration according to the conventional example described above can be changed. In the same way, see -3000ppm/"C
The temperature coefficient can be freely set within the range from +3000 ppm/"C!" and, on the other hand, the usable power supply voltage range can be made almost unrelated to the temperature coefficient that is selectively set.

Further, FIG. 2 shows a circuit configuration according to another embodiment of the present invention, and in this embodiment circuit of FIG.
and second resistors R1 and R2 are respectively grounded, and third and fourth PNP transistors Q6. Q7 and output terminal T. , T are inserted on the power supply side, and the same operation and effect as C can be obtained from the circuit of the embodiment shown in FIG.

〔Effect of the invention〕

As detailed above, according to the present invention, in the conventional circuit configuration, the first resistor is connected between the emitters of the first and second NPN transistors, and the first resistor is connected between the emitters of the second and third NPN transistors. 2nd in between
Since the third resistor is omitted and the emitter of the second NPN transistor is used as the output terminal, the temperature coefficient can be freely selected over a wide range, and the usable power supply voltage range can be adjusted. , has the advantage of being almost independent of the set temperature coefficient, and the number of circuit components can be reduced by omitting the third resistor, and the resistance value of each resistor can be easily selected in the integrated circuit, resulting in This type of constant current circuit has excellent features such as being able to be constructed relatively easily and at low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit connection diagram showing one embodiment of the constant current circuit according to the present invention, FIG. 2 is a circuit connection diagram showing another embodiment of the same, and FIG. 3 is a conventional example of the above circuit. It is a circuit connection diagram. Q...First PNP transistor, Q2...
2nd PNP transistor, Q3... NPN in field 1
Transistor, Q...Second NPN transistor, Q5...Third NPN transistor, R, -
...First resistance, R2...Second resistance, T...
...Output terminal. UT Agent Masuo Oiwa Figure 1 Ql: Nu I = 1 PNP ゛゛゛ Matari Q2: 't12
PNP ￥F, Q3:vll qNPN)
'7; Ji° again Q4 decay 2 NPN transverse space R2: second resistance TOLIT: Ekahanawa 3

Claims (1)

[Claims] A first PNP transistor whose collector and base are connected to each other and whose emitter is connected to a power supply;
a second PNP transistor connected to the base of said PNP transistor and having its emitter connected to the power supply; a first PNP transistor having its collector connected to the collector of said first PNP transistor;
an NPN transistor, the collector of which is connected to the collector of the second PNP transistor, and the base of which is connected to the collector of the first NPN transistor.
a second NPN transistor connected to the base of the PN transistor, a third NPN transistor whose base is connected to the collector of the second NPN transistor, whose emitter is connected to the base of the second NPN transistor, and whose collector is connected to the power supply.
a first resistor connected between the emitters of the first and second NPN transistors, a second resistor connected between the emitters of the second and third NPN transistors; A constant current circuit characterized in that the emitter of the NPN transistor No. 2 is used as an output terminal.