JPH0749537Y2 - Constant current generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention relates to temperature characteristics of a constant current obtained from a constant current source, and more particularly to a constant current generation circuit used in a linear IC.

2. Description of the Related Art FIG. 4 shows a constant current generating circuit called a current mirror circuit which is well known in the prior art. In this circuit,
Resistor R10 collector power supply terminal 2 and the transistor Q _10, which is connected between the common connection point based base and the transistor Q _11, the emitters of the transistors Q10, Q11 is
It is connected to the GND terminal 3 which is grounded. The collector of the transistor Q11 is connected to the constant current output terminal 1.

Now, assuming that the current amplification factors of the transistors Q10 and Q11 are sufficiently large and the base current can be ignored, the transistor Q10
And Q11 form a current mirror, transistor Q10
And the ratio of the currents I1 and I2 flowing through the collectors of Q11 is proportional to the emitter pattern size of the transistor.

That is, Becomes

Here, AEQ10 and AEQ11 are transistors Q10 and Q1 respectively.
Represents 1 emitter pattern area.

Therefore, the current I2 flowing through the transistor Q11 is the power supply terminal 2
The voltage applied to Vcc is Vcc, and the forward voltage between the base and emitter of transistor Q10 is VBEQ10. Becomes

Problems to be Solved by the Invention By the way, the temperature characteristics of the constant current I2 obtained by the above-described conventional method largely depend on the temperature characteristics of the base-emitter forward voltage VBEQ10 and the resistance R10 of the transistor Q10.

That is, the amount of change in the constant current I2 with respect to the operating temperature T is calculated by using the above equation, Becomes

Therefore, a linear IC or the like using a constant current obtained by the conventional method has a drawback that there is a change in circuit current due to temperature and a change in characteristics due to a change in operating point in the circuit.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to correct the above-mentioned drawbacks and provide a constant current generating circuit with a small temperature change easily designed.

Further, it is to easily provide a constant current circuit having a desired rate of change with respect to temperature, if necessary.

Therefore, the constant current generating circuit of the present invention comprises a constant voltage generating circuit,
The voltage-current conversion circuit includes a voltage-current conversion circuit that receives the voltage as an input and that has a small change due to temperature to obtain a predetermined voltage, and a voltage-current conversion circuit that outputs the voltage as a constant current. Is composed of a transistor having an input terminal and an output terminal, respectively, and a current setting resistor connected to its emitter, the current setting resistor being set according to its temperature coefficient,
The change in the voltage drop due to the temperature when the set current is passed is the change in the base-emitter voltage of the transistor due to the temperature, and if the constant voltage generating circuit has temperature characteristics, the output of the voltage-voltage conversion circuit based on it It is characterized in that the constant current is selected to have a resistance value that causes a desired change with temperature in combination with a change in voltage with temperature.

According to the present invention, as the constant voltage generating circuit, a known circuit such as a bandgap circuit, which has no degree of freedom in voltage value but has a small change with temperature, can be used.
There is no difficulty in designing. As a voltage-voltage conversion circuit whose change with temperature is small, for example, the amplification factor of a voltage amplifier is determined 2
It can be easily made by making the temperature coefficients of the individual feedback resistors the same (that is, they can be made by the same manufacturing method), and there is no difficulty in design because the conversion rate is set only by selecting the resistance ratio.

In the case of a voltage-current conversion circuit, when the set constant current requires a desired change with respect to temperature, the current setting resistor is a resistor so that the change in voltage drop due to the set current due to temperature is desired. The input voltage can be easily set by selecting the value and then selecting the conversion ratio of the voltage-voltage conversion circuit.

For example, a case where a constant current circuit whose change with temperature is small is required will be described. When the change of the output of the constant voltage generation circuit with respect to temperature is small, the output of the voltage-voltage conversion circuit also changes with respect to temperature. The voltage applied to the current setting resistor is the voltage obtained by subtracting the base-emitter voltage of the transistor from the output voltage of the voltage-voltage conversion circuit (small change due to temperature), and the base-emitter voltage of the transistor does not depend on temperature. Then, the voltage applied to the current setting resistor changes positively, which has the effect of changing the constant current positively with respect to temperature. Since the resistance value of the current setting resistor changes positively with respect to temperature, it has the effect of making a negative change with respect to temperature with respect to the constant current.

Therefore, if a resistor that makes the output current fluctuation due to the temperature change of the current setting resistor the same as the output current fluctuation due to the temperature of the base-emitter voltage of the transistor is selected as the current setting resistor, An extremely small constant current can be obtained. If the temperature coefficient of resistance is known, there is no design difficulty because the resistance value is simply selected to select such resistance.

Then, it is easy to set the output voltage of the voltage-voltage conversion circuit so that a desired current value can be obtained with respect to the resistance value thus selected, because the conversion ratio can be set.

Further, when it is desired that the constant current circuit has a change with respect to a certain temperature, it is easy to select the current setting resistor as such.

In the above, the case where the output voltage of the constant voltage generation circuit has a small change with temperature and can be ignored, but there are changes that cannot be ignored, and therefore the output voltage of the voltage-voltage conversion circuit has a change with temperature that cannot be ignored. The current setting resistor can be selected so as to correct it when there is.

Embodiment 1 An embodiment of the present invention will be described below with reference to FIG.
The constant current generating path shown in FIG. 1 is a constant voltage generating circuit 4 which supplies a stable voltage regardless of temperature change, and a voltage required by a voltage amplifier Ampl having the constant voltage as an input and having a feedback resistor RA.RB. The voltage-current conversion circuit 5 for generating the voltage and inputting it to the base of the transistor Q1 and the emitter of the transistor Q1 are grounded via the resistor R0, and a constant current is obtained from the collector of the transistor Q1. And a conversion circuit 6.

FIG. 2 is a more detailed description of the constant current generating circuit having the above-mentioned configuration. The constant voltage generating circuit 4 includes a transistor Q2,
A band having a starter circuit 7 composed of resistors R1 and R2 and diode setting transistors Q3 and Q4, a current mirror circuit 9 having a constant current terminal 8 and an emitter resistor R8, and a current mirror circuit 10 connected to a sidestream transistor Q5. And a gap circuit 11. The voltage-voltage conversion circuit 5 includes a current mirror circuit 12, a differential amplifier 13 having transistors Q6 and Q7 having the same characteristics, an output amplification stage Q8, and feedback resistors RA1, RA2 and RB. Here, the output amplification stage
The output of Q8 is connected between the feedback resistors RA1 and RA2, that is, from the midpoint of R4 to the base of the transistor Q1 of the voltage-current conversion circuit 6, but in principle it is different from the circuit of FIG. Not a thing.

The operating principle of the constant current generating circuit described above is as follows.

The voltage VR generated by the constant voltage generation circuit 4 is the voltage amplifier Ampl (1
3), amplified by a non-inverting amplifier circuit composed of resistors RA and RB, the output voltage V0 of the voltage amplifier Ampl is given by V0 = (1 + RA / RB) VR ... (1).

Here, VR does not have a temperature characteristic, and RA and RB have the same temperature coefficient if they are manufactured by the same manufacturing method although they change depending on the temperature, respectively, so that the ratio does not have a temperature characteristic. Therefore, V0 has no temperature characteristic.

Assuming that T0 is room temperature, T is operating temperature, the room temperature resistance value of the resistor R0 is R0 (T0), the temperature coefficient is x / ℃, and the resistance value at operating temperature is R0 (T), R0 (T) = R0 (T0) · {1 + x (T-T0)} (2) Also, the base-emitter forward voltage of the transistor Q1 is VBEQ1 (T0) at room temperature, and the change with temperature is yV / ° C at operating temperature. If the value is VBEQ1 (T), VBEQ1 (T) = VBEQ1 (T0) + y (T-T0) ... (3) Collector current of transistor Q1, that is, the constant current value at room temperature is IR (T0) , IR (T) is the value at the operating temperature, IR (T) = {V0-VBEQ1 (T)} / R0 (T) (4) As mentioned above, V0 has temperature characteristics. Not as IR
When IR is differentiated by T to obtain the change with temperature, ∂IR (T) / ∂T = [− R0 (T) ・ VBEQ1 ′ (T) −R
0 '(T) ・ {V0-VBEQ1 (T)}] / {R0 (T)} ² ………
(5) Here, VBEQ1 '(T) = ∂VBEQ1 (T) / ∂T = y from equation (3) ... (6) From equation (2) R0' (T) = ∂R0 (T) / ∂T = x ・ R0 (T0) …………
(7) By substituting the equations (6) and (7) into the equation (5), ∂IR (T) / ∂T = [− R0 (T) · y−x · R0 (T0) ·
{V0-VBEQ1 (T)}] / {R0 (T)} ² (8) Therefore, assuming that the desired value αA / ° C is the change in IR near room temperature, at T = T0, equation (8) becomes α = [− R0 (T0) · y−R0 (T0) · x {V0−VBEQ1 (T
0)}] / {R0 (T0)} ² =-[y + x {V0-VBEQ1 (T
0)}] / R0 (T0) ………… (9) Here, assuming that the desired constant current value (normal temperature) is IR (T0), R0 (T0) = {V0-VBEQ1 (T0) from formula (4). } / IR (T0) ………… (1
0) When Eq. (10) is substituted into Eq. (9) and rearranged, V0-VBEQ1 (T0) = IR (T0) ・ y / {α + IR (T0) ・ x} Therefore, V0 = -IR (T0) ・ y / {Α + IR (T0) ・ x} + VBEQ1 (T
0) ………… (11) where x, y, VBEQ1 (T0) is a constant value and α, IR (T0) is the desired (given) value, so V0 can be easily determined and the resistance value R0 (T0) can also be easily determined from equation (10).

Here, considering the case where the change due to temperature is minimized, that is, α = 0, the equation (11) is V0 = −y / x + VBEQ1 (T0) ……………… (11 ′) For example, IR = IR (T0) = 1mA, VBEQ1 (T0) = 0.7V, x = 200
When determining R0, RA, and RB with 0PPM / ° C, y = −2mV / ° C, VR = 1.25V, V0 = − (− 2 × 10 ₋₃ / 2 × 10 ₋₃ ) from the equation (11 ′) + 0.7 = 1.7V Therefore, from the equation (10), R0 = (1.7−0.7) / 10 ₋₃ = 1kΩ Further, from the equation (1) RA / RB = V0 / VR-1 = 1.7 / 1.25-1 = 0.36 where , RB = 1 kΩ RA = 0.36 × 10 ₃ = 360 Ω From the above, by setting R0 = 1 KΩ, RA = 360 Ω, RB = 1 KΩ, a constant current with an extremely small temperature change can be obtained at IR = 1 mA.

Embodiment 2 FIG. 3 shows an application example in which the voltage VR generated in the constant voltage generation circuit is higher than the input voltage V0 to the voltage-current conversion circuit obtained by the above-mentioned equation (11).

The input voltage V0 to the voltage-current conversion circuit is And a constant current with a small temperature change can be set by the equations (11 ') and (12).

As is apparent from the above, according to the present invention, it is possible to supply a constant current whose temperature change is extremely small, and it is also possible to supply a constant current source having an arbitrary temperature coefficient by using the equation (9).

Further, in this embodiment, the input voltage V0 to the voltage-current conversion circuit is
Although the description was made assuming that the temperature change of 0V / ° C, it is also applicable when there is a temperature change.

That is, assuming that the temperature change of the input voltage V0 is ZV / ° C, the equation (4) is differentiated by T, and ∂IR (T) / ∂T = [R0 (T) ・ {V0 '(T) -VBEQ
1 '(T})-R0' (T) ・ {V0-VBEQ1 (T)}] / {R
0 (T)} ² ………… (13) Here, if the value of the voltage amplifier Ampl at room temperature is V0 (T0), V0 (T) = V0 (T0) + z (T−T0) V0 ′ (T) = ∂V0 (T) / ∂T = z ………… (14) Substituting Eq. (13) for Eqs. (6), (7), and (14), ∂IR (T ) / ∂T = [(z−y) ・ R0 (T) −R0 (T0)
・ X ・ {V0 (T) -VBEQ1 (T)}] / {R0 (T)} ² ………
(15) Here, assuming that the change of the current IR due to temperature around room temperature is αA / ° C and T = T0, α = [(z−y) · R0 (T0) −R0 (T0) · x { V0 (T0)
−VBEQ1 (T0)] / R0 (T0) ……………… (16).

Therefore, using equation (16) instead of equation (11),
If constants are set in Eq. (4), x, y, zVBEQ1 (T0) is a constant value, and α, IR (T0) is a desired (given) value, so V0 (T0) or R0 (T0) can be easily determined.

Therefore, it is easy to use a constant current circuit with no temperature change (α = 0) or a constant current circuit with a desired temperature change.

Next, when the change of V0 (T) with respect to temperature changes in the form of V0 (T) = V0 (T0) {1 + w (T-T0)}, V0 '(T) = ∂V0 (T) / ∂T = V0 (T0) ・ w …………
(13 ') is obtained, and when equations (6), (7), and (13') are substituted into equation (13) and the same processing as above is performed, α = [{V0 (T0) · w−y} −x · {R0 (T0) −VBEQ1
(T0)} / R0 (T) ………… (16 ′) is introduced.

Therefore, using equation (16 ') instead of equation (11),
If the constants are set in equation (4) and, x, y, w, VBEQ1 (T0) is a constant value, and α, IR (T0) is a desired (given) value, so V0 (T0) And R0 (T0) can be easily determined.

Therefore, it is easy to use a constant current generation circuit with no temperature change (α = 0) or a constant current generation circuit with a desired temperature change.

Effects of the Invention As described above, according to the present invention, a constant current generating circuit whose change with temperature is extremely small and a constant current generating circuit having a desired temperature coefficient are easily provided.

Therefore, when the constant current generating circuit according to the present invention is used in a linear IC or the like, various characteristics with respect to changes in temperature can be brought out.

[Brief description of drawings]

1 and 2 are circuit diagrams showing an embodiment of the present invention, FIG. 3 is a circuit diagram showing another embodiment, and FIG. 4 is a circuit diagram showing a constant current source generally used in the past. is there. 4 ... Constant voltage generation circuit, 5 ... Voltage-voltage conversion circuit, 6
...... Voltage-current conversion circuit, Q1, Q10, Q11 ...... Transistor, RA, RB, RA ₁ , RA ₂ ...... Resistor, Ampl (13) ...... Voltage amplifier, R ₀ ...... Current setting resistor.

Claims (1)

[Scope of utility model registration request] 1. A constant voltage generation circuit, a voltage-voltage conversion circuit which receives the voltage as an input and obtains a predetermined voltage with a small change due to temperature, and a voltage-current conversion circuit which inputs the voltage and outputs a constant current. The voltage-current conversion circuit includes a transistor having a base and a collector as an input terminal and an output terminal, respectively, and a current setting resistor connected to its emitter, and the current setting resistor is set according to its temperature coefficient. Is
The change in the voltage drop due to the temperature when the set current is passed is the change in the base-emitter voltage of the transistor due to the temperature, and if the constant voltage generating circuit has temperature characteristics, the output of the voltage-voltage conversion circuit based on it A constant current generating circuit characterized in that the constant current is selected to have a resistance value such that the constant current makes a desired change with respect to the temperature in combination with a change in voltage with temperature.