JPH02188811A - Constant current circuit - Google Patents

Abstract

PURPOSE:To acquire a current which is proportional to an absolute temperature with use of a small number of elements by generating the voltage proportional to the absolute temperature by means of the absolute temperature dependence of the base-emitter voltage of a transistor, and converting the voltage into a current. CONSTITUTION:A constant voltage source VC generates the constant voltage having no dependence on the ambient temperatures and the power voltage VB. The base-emitter voltage of an npn transistor TR Q6 has the temperature dependency, therefore the current flowing to a resistance R2 is proportional to temperatures. The source VC always generates the voltage of a fixed level regardless of the temperatures and the voltage VB. Therefore the oscillation due to the change of the voltage VB is never generated. The collector currents are equal to each other between the TR Q6 and Q5 as long as both TRs have the same form. The collector current is taken out of the collector of the TR Q5 and supplied to another circuit. Thus no oscillation preventing capacitor is required and a current proportional to an absolute temperature is obtained with use of a small number of elements.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a constant current circuit that generates a current proportional to absolute temperature.

[Conventional technology]

FIG. 5 is a circuit diagram showing a conventional constant current circuit that generates a constant current proportional to absolute temperature. In the figure, B is a first current mirror circuit, and PNP transistors Q1.
Consists of Q2. The first current mirror circuit B uses the transistor Q1 as a reference, and the transistor Q1. The collector area ratio of Q2 is 1:α. ]・Langister Q1. The emitter of Q2 is connected to power supply ■8.

D is a second current mirror circuit, which includes NPN transistors Q3. It consists of Q4 and resistor R1.

The second current mirror circuit uses transistor Q4 as a reference and transistors Q3. The emitter area ratio of Q4 is β
:1. The transistor Q3 has a relief connected to the collector of the transistor Q1, and an emitter grounded through a resistor R1.

The collector of the transistor Q4 is connected to the collector of the transistor Q2, and the emitter is grounded.

C is a capacitor for preventing oscillation when the power supply voltage V8 fluctuates, and transistors Q1. It is connected between the collector common connection point of Q3 and the collector common connection point of transistors Q2 and Q4.

Q5 is an NPN transistor forming a current mirror with transistor Q4, and its collector is connected to the power supply VB via a monitoring ammeter A, and its emitter is grounded.
Its base is connected to the base of transistor Q4.

Next, the operation will be explained. Now, assume that the collector currents of each of transistors Q1 and Q2 are rl and 12. Since the collector area ratio of transistors Q1 and 02 is 1:α, I2 = α・11 (1)
becomes. Also, transistor Q3. It is assumed that the emitter area of Q4 is β:1. Here, the base-emitter voltages of transistors Q3 and Q4 are respectively vBE3°V8,4,
If the voltage generated across the resistor R1 is Δv1, then Δ■1−■BE4 VBE3 k: Boltzmann constant T: absolute temperature q: electron charge amount ■S: saturation current. The current 11/β flowing through the resistor R1 is I 1
ΔV1 β R1 (3). From equations (1), (2), and (3), ■2−α1
It becomes 1. In equation (4), α, β, q, and R have no temperature dependence. Therefore, the current I2 becomes a current proportional to the absolute temperature T. Here, transistors Q4 and 05
If the emitter shapes of transistors Q4 and Q05 are made the same, the collector currents of transistors Q4 and Q05 will be approximately equal, and this current will be applied to other circuits from the collector of transistor Q5.

Ammeter A monitors this current.

(Problems to be Solved by the Invention) The conventional constant current circuit is configured as described above and is provided with a capacitor C for preventing oscillation, so the number of elements increases and the cost increases with the increase in the number of elements. There was a problem.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a constant current circuit that eliminates the need for an oscillation prevention capacitor, has a small number of elements, and generates a current proportional to absolute temperature. do.

(Means for Solving Problem 11) A constant current circuit according to the present invention includes a constant voltage source that generates a constant voltage that is not affected by absolute temperature, and a transistor, and a constant voltage source that generates a constant voltage that is not affected by absolute temperature from the constant voltage source. is given, temperature-dependent voltage generation means generates a voltage proportional to absolute temperature by utilizing the absolute temperature dependence of the same voltage between the base and emitter of the transistor, and the voltage from the temperature-dependent voltage generation means is converted into a current. The configuration includes a voltage-to-current conversion resistor that converts the voltage to the current.

[Effect]

The constant voltage source in this invention generates a constant voltage that is not affected by absolute temperature, and the temperature dependent voltage generating means receives this constant voltage and uses the absolute temperature dependence of the same voltage between the base and emitter of the transistor to generate a constant voltage that is not affected by absolute temperature. Generates a proportional voltage. A voltage-to-current conversion resistor converts this voltage into current.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention that generates a constant current. In the figure, the differences from the conventional circuit shown in FIG. 5 are as follows: 1. Eliminate the second current mirror circuits B, D and capacitor C, and replace them with transistor Q6 and constant voltage source (2). This is because we have established the following.

It is assumed that the constant voltage source VC generates a constant voltage that is independent of the ambient temperature and the power supply voltage VB.

Transistor Q6 is an NPN transistor, and its collector is a constant voltage source ■. The emitter is connected to ground through a resistor R2. A resistor R3 is connected between the base and collector of the transistor Q6, and a resistor R4 is connected between the base and emitter of the transistor Q6. Other configurations are the same as before.

Next, the operation will be explained. The collector-emitter voltage of the transistor Q6 is v1 The base-emitter voltage is V1 The resistors E6 of the resistors R3 and R4 are R3 and R4, respectively. The base-emitter voltage VBE is generally 25
℃, and the relationship between the base-emitter voltage V8E6 and the temperature T8 in degrees Celsius is expressed as follows, with 25℃ as the reference: V BE6 : vBE6 (25) BE6 (25)
+V.

CF2 VBE6 (25): Voltage between the base and emitter of transistor Q6 at 25° C. T: Celsius temperature Substituting equation (6) into equation (5) gives the following equation (7).

Now, constant voltage source V. The voltage of VC=N” vBE6(25) −(
8). Here, N is an arbitrary constant. Then, if the voltage applied across the resistor R2 is Δ■2, then Δv2”
"N" V BE6 (25) CF2-V
...(9) becomes. Substituting equation (1) into equation (9) gives ΔV”' ”
' ” ” VBE6 (25) BE6 (25) -
■...(10) becomes.

Here, since 1+R3/R4 has no temperature dependence, for example, the resistance values of resistors R3 and R4 are adjusted to become 1+R3/R4. Substituting equation (11) into equation (10) and sorting it out gives...(12). Figure 2 is a diagram illustrating the physical meaning of equations (9) and (125), and it can be seen that the voltage Δ■2 across the resistor R2 is proportional to the temperature T. If the flowing current is 'R2, then Δv2 R2-12 do 2 is obtained. In equation (13), N'' VBE6 (25)
/ (2・R2) has no temperature dependence. Therefore, the current I R2 flowing through the resistor R2 becomes a current proportional to the temperature T. Constant current source V always generates constant voltage N・■ regardless of temperature and power supply voltage VB.
), oscillations due to changes in the power supply voltage (8) do not occur as in the conventional case.

Now, if the emitter shapes of transistors Q6 and 05 are made the same, the collector currents of transistors Q6 and 05 will be approximately equal, and this current will be taken out from the collector of transistor Q5 and applied to other circuits.

The collector current of transistor Q5 is monitored by ammeter A.

FIGS. 3 and 4 are circuit diagrams showing other embodiments of the present invention. In Figure 3, V = 2 V BE (25
). Q7 is an NPN transistor whose emitter is grounded through a resistor R2 and whose collector is connected to the power supply voltage V through an ammeter A.

, the bases are each connected to a constant voltage source vc.

In FIG. 4, it is set so that ■=3■8E (25). In this circuit, an NPN transistor Q8 is roughly provided at the base of the transistor Q7 shown in FIG. The emitter of the transistor Q8 is grounded through the resistor R5, and is also connected to the base of the transistor Q7, with the collector connected to the power supply voltage ■ and the base connected to the constant voltage source ■. are connected to each. The voltages generated across the resistor R2 in Figures 3 and 4 are different, and as is clear from equations (14) and <15), the current flowing through the resistor R2 is proportional to the temperature T. .

In the above embodiment, the constant voltage source was set based on the base-emitter voltage vBE (25) at 25° C., but any constant voltage source may be used as long as it can generate a constant voltage that is not affected by temperature.

Furthermore, in the above embodiment, N in equation (8) is 2(1+R3/
R4), 2.3 has been explained, but in the case of N such that transistor Q6 or Q7 in the above embodiment is conductive,
It can be any value.

〔Effect of the invention〕

As described above, the constant current circuit according to the present invention includes a constant voltage source that generates a constant voltage that is not affected by absolute temperature, and a transistor, and is provided with a constant voltage that is not affected by absolute temperature from the constant voltage source, and Temperature-dependent voltage generation means that generates a voltage affected by absolute temperature by using the absolute temperature dependence of the voltage between the base and emitter of a transistor, and a voltage that converts the voltage from the temperature-dependent voltage generation means into a current. Since the current converting resistor is provided, there is no need to provide a capacitor for preventing oscillation, and a current proportional to the absolute temperature can be generated with a small number of elements.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of this invention, FIG. 2 is a diagram showing the relationship between temperature and voltage in the circuit of FIG. 1, and FIGS. 3 and 4 are other embodiments of this invention. A circuit diagram showing an example, FIG. 5 is a circuit diagram showing a conventional constant current circuit. In the figure, ■o is a constant voltage source, R2 is a resistor, and Q6 is an NP
It is an N transistor. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A constant voltage source that generates a constant voltage unaffected by absolute temperature, and a transistor, the constant voltage source providing a constant voltage unaffected by absolute temperature, and the base-emitter voltage of the transistor depending on the absolute temperature. 1. A constant current circuit comprising: temperature-dependent voltage generation means that generates a voltage proportional to absolute temperature by using the temperature-dependent voltage generation means; and a voltage-current conversion resistor that converts the voltage from the temperature-dependent voltage generation means into a current.