JPH0230047B2 - KIKANZOFUKUKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a feedback amplifier circuit, particularly a compensation circuit suitable for improving the power supply voltage characteristics of a control device that controls the voltage, current, etc. supplied to a load at a constant level, and is extremely suitable for application to integrated circuits. This invention relates to an effective feedback amplifier circuit.

A feedback amplifier circuit receives a load drive signal as a negative feedback signal and is used to apply a constant voltage or flow a constant current to the load, but it has the disadvantage that its output changes with fluctuations in the power supply voltage. Ta.

One of the reasons for this is considered to be the characteristics of the elements constituting the feedback amplifier circuit, especially the influence of the Early effect of the transistor. The Early effect is that even though the base bias is constant, when the collector potential relative to the emitter potential of the transistor fluctuates, the value of the flowing current changes in accordance with the fluctuation. Therefore, when the current source in the feedback amplifier circuit is constructed from a transistor, the current flowing changes depending on the fluctuation of the current and voltage, and the operating current of the circuit changes, making it impossible to obtain a constant voltage. SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a feedback amplifier circuit that improves the deterioration of power supply voltage characteristics caused by these Early effects and provides a stable output even when the power supply voltage fluctuates.

The present invention addresses fluctuations in collector current due to the Early effect of a transistor used as a current source.
The present invention is characterized in that a current of the same amount and opposite polarity as the variation is generated, and this current is added to the transistor to cancel the variation in the collector current of the transistor.

Hereinafter, the present invention will be explained in more detail using the drawings.

FIG. 1 is a circuit diagram showing a typical conventional control circuit equipped with a feedback amplifier circuit.
Terminal 1 and terminal 2 of terminal 00 are power supply voltage supply terminals, and terminal 3 is an output terminal to which load 200 is connected. The reference voltage generating circuit 1 generates a constant voltage between its input and output terminals c and d, and also has a reference voltage terminal e. This output terminal d is connected to one input terminal a of the comparison amplifier 2, and the voltage of the output terminal 3 is applied to the other input terminal b. This comparison amplifier 2 is a differential amplifier composed of transistors Q ₁ , Q ₃ , Q ₄ and resistors R ₄ , R ₅ , R ₆ .
The output signal of comparison amplifier 2 is transmitted through transistor Q ₅ ,
After being amplified by a so-called current mirror amplifier 4 consisting of a diode D ₁ and resistors R ₇ and R ₈ , the output circuit 5 is driven. The transistor _Q2 constitutes a constant current source 3 by having its base connected to the reference voltage terminal e of the reference voltage generating circuit 1, and the amplifier 4
This is the transistor that serves as the load for transistor _Q5 . Therefore, the current i ₄ driving the output circuit 5 is the constant current i 3 of the constant current source ₃ minus the collector current i ₅ of the transistor Q ₅ .

The output of the output circuit 5 is supplied to the load 200 and at the same time is applied to the input terminal b of the comparator amplifier 2,
It is compared with a reference voltage generated by the reference voltage generation circuit 1, and the voltage or current supplied to the output is controlled to be constant.

If the power supply voltage Vcc fluctuates and rises to Vcc', the load current i _R and the load voltage V _R will remain constant as long as the load 200 remains constant due to the effect of negative feedback. If the load current i _R is constant, the input current i ₄ of the output circuit 5 is also constant. On the other hand, regarding the current i ₃ determined by the constant current source 3 for driving the output circuit, the voltage between the collector and emitter of the transistor Q ₂ that is a component thereof is biased with the input terminal of the output circuit 5 being biased with respect to the terminal 2. In this case, the collector potential is almost constant, and the emitter potential changes depending on the power supply voltage, so it changes greatly depending on the power supply voltage. Therefore, due to the early effect, the collector current of transistor Q ₂ which was i ₃ at power supply voltage Vcc becomes i ₃ + at power supply voltage Vcc'.
Changes to △i ₃ . In other words, the value of the power supply voltage is Vcc
At this time, the collector current i ₅ of the transistor Q ₅ becomes i ₅ = i ₃ − i ₄ (1), where the drive current for driving the output circuit 5 is i ₄ , and the power supply voltage changes to Vcc'. When this happens, the amount of electricity supplied to the load is controlled by a negative feedback loop so that it is constant, so i ₅ ′=i ₃ +△i ₃ −i ₄ (2). Therefore, the current generated due to a change in the power supply voltage
The change in i ₅ △i ₅ is △i ₃ = △i ₅ (3). Assuming that the amplifier 4 has a current amplification degree A, the change Δi ₆ in the collector current of the transistor Q ₄ becomes Δi ₆ =A·Δi ₅ (4). Here, the reference voltage generating circuit 1 has its input,
It produces a constant voltage between output terminals c and d,
Therefore, when the power supply voltage fluctuates, the potential at the output terminal d also changes accordingly. By the way, transistor
The emitter-collector voltage of Q ₁ is always constant, and the collector current i ₆ of transistor Q ₄ does not change. However, since the current i ₃ of the constant current source 3 changes, the current i ₆ changes. Therefore, if the change in voltage drop due to the Early effect of the transistor Q ₂ at the resistor R ₆ of the comparator amplifier 2 is △V, then normally R ₅ = R ₆ is set, so (3), (4) From this, △V=2・A・R ₆・△i ₃ ......(5).

The reason why the equation (5) is doubled is because comparator amplifier 2 is equivalently a differential amplifier. In other words, when the current of transistor Q ₄ increases by △i ₆ , the current of Q ₃ becomes This is because △ _i6 decreases.

In this way, in the conventional control circuit 100, since the voltage drop variation of the resistor 6 is ΔV expressed as in equation (5), when the power supply voltage becomes Vcc' from Vcc, the voltage between terminals 1 and 3 becomes V _{1- 3} also corresponds to a △V change, which means that the load terminal voltage V _R changes and the load inflow current i _R changes.

Hereinafter, a control circuit equipped with a feedback amplifier circuit according to the present invention will be explained in detail. FIG. 2 is a circuit diagram of a control circuit showing one embodiment of the present invention, and FIGS. 3, 4, and 6 show application examples using the control circuit of the present invention, and in particular, FIG. 6 is for motor speed control. This is an example used as an example. FIG. 5 also shows a motor speed control circuit using a conventional control circuit.

In FIG. 2, the same parts as in FIG. 1 are designated by the same numbers and symbols, and their explanations will be omitted.
The difference is that the transistors Q ₆ and Q ₇ whose bases are connected to the reference voltage terminal e of the reference voltage generation circuit 1
are provided and connected to terminal 1 via respective emitter resistors R ₁₀ and R ₁₅ . The collector of the transistor Q ₆ is connected to the diode D ₂ of a current mirror circuit 8 composed of a transistor Q ₉ , _a diode D ₂ and resistors R ₁₁ and R ₁₂ .
The collector of is connected to the collector of transistor _Q5 . The collector of transistor _Q7 is connected to diode _D3 via the collector and emitter of transistor _Q8 . Transistor Q ₈
The base of is connected to the output terminal d of the reference voltage generating circuit 1. Diode D ₃ forms a current mirror circuit 9 together with transistor Q ₁₀ and resistors R ₁₁ and R ₁₄ .
, and the collector of transistor Q ₁₀ is connected to the collector of transistor Q ₆ .

In the control circuit 100 of this embodiment, the base potential of the transistor Q ₈ is individually determined by the potential of the output terminal d of the reference voltage generation circuit 1, so that the collector-emitter voltage of the transistor Q ₇ of the constant current source 7 are the input and output terminals c,
Since it is fixed at a voltage obtained by subtracting the base-emitter voltage V _BE of transistor Q ₈ from the voltage across d, it is not affected by fluctuations in the power supply voltage, and there is almost no Early effect. Yotsute transistor
The collector current _i8 of _Q8 is not affected by the Early effect and remains constant. On the other hand, the transistor of constant current source 6
The voltage between the collector and emitter of Q ₆ is determined by the diode D ₃ whose collector potential is referenced to the ground terminal 2.
Since the current i 7 is fixed at a potential raised by the sum of the forward voltage of and the voltage drop of the resistor R ₁₄ , the current i ₇ changes due to the Early effect due to fluctuations in the power supply voltage.

Further, as already mentioned, the transistor Q ₂ of the constant current source 3 is subjected to the Early effect due to fluctuations in the power supply voltage, and its current i ₃ changes.

Therefore, due to the constant current i ₈ which is not affected by the Early effect and the current mirror circuit 9, a current i ₁₁ which is proportional to the current i ₈ and which is not affected by the Early effect flows through the transistor Q ₁₀ . This current i ₁₁ is drawn from transistor Q ₆ and is not affected by the Early effect as described above, so this current
When i ₁₁ is subtracted from the current i ₇ affected by the Early effect, a current i ₁₀ corresponding to the current change due to the Early effect flows through the diode D ₂ and the resistor R ₁₂ . Then, the current mirror circuit 8 causes a current ii ₉ proportional to i ₁₀ to flow. Therefore, since the current i ₉ is proportional only to the change in current due to the Early effect, the change Δi ₃ due to the Early effect in i ₃ determined by the constant current source 3, which is the load of the transistor Q ₅ , is the current due to the above circuit configuration. i ₉ , and the voltage V _1-3 between terminals 1 and 3 can be made a constant voltage that has no dependence on the power supply voltage.

In order to make it easier to understand, the above is expressed as a mathematical formula. First, the base voltage of transistor _Q10 V _B10
is V _B10 = V _BEQ10 + i ₁₁ · R ₁₃ = V _BED3 + i ₈ · R ₁₄ . V _BEQ10 = KT/qlni ₁₁ /i _S1 , V _BED3 = KT/qlni
₈ /i _S2 , so KT/qlni ₁₁ /i _S1 /i ₈ /i _S2 = i ₈・R ₁₄ −i ₁₁・R ₁₃ . Here, R ₁₁ and R ₁₄ are resistances R _{13 and} R 14 , respectively.
The resistance value of _R14 , q is the electronic charge, k is the Boltzmann constant, T is the absolute temperature, and i _S1 and i _S2 are the dark currents of the transistor Q ₁₀ and the diode D _3, respectively. i _S2 /i _S1
is determined by the ratio of the emitter area of _Q10 and the cathode area of _D3 , and if that ratio is J, then _i11 = _i8・_R14 −KT/qln(J・_i11 / _i8 )/ _R13. Become. Since the current change i ₁₀ due to the Early effect of transistor Q ₆ is i ₁₀ = i ₇ − i ₁₁ , i ₁₀ = i ₇ − i ₈・R ₁₄ −KT/qln(J・i ₁₁ /i ₈ )/ R ₁₃ ......(6).

Next, the base voltage V ₉ of the transistor Q ₉ is V _B9 = V _BEQ9 + i ₉ · R ₁₁ = V _BED2 + i ₁₀ · R ₁₂ , so if we do the same as above, i ₉ = i ₁₀ · R ₁₂ − KT/qln(J'・i ₉ /i ₁₀ )/R ₁₁ ...
…(7) becomes. Here, R ₁₁ and R ₁₂ are resistances R _{11 and} R 12 , respectively.
is the resistance value of R ₁₂ , and J' is the ratio of the emitter area of transistor Q ₉ to the cathode area of diode D ₃ .

In a semiconductor integrated circuit, diodes D ₂ and D ₃ are composed of base-collector shorted transistors. Therefore, by forming the circuit 400 as an integrated circuit formed on a single semiconductor substrate, the condition of equation (8) below can be obtained.

By substituting these into equations (6) and (7), i ₉ = i ₁₀ = i ₇ − i ₈ ......(9). Therefore, the variation _i10 due to the Early effect of the transistor _Q6 becomes the current _i9 and is drawn from the collector of the transistor _Q2 .

At this time, the collector current of transistor _Q2 is
i ₃ ′ becomes i ₃ ′ = i ₃ + △i ₃ (10) due to fluctuations in the power supply voltage. This collector current i ₃ becomes the collector current of the transistor Q ₅ and the drive current i ₄ that drives the output circuit 5, and also serves as the collector current i ₉ of the transistor Q ₉ . Therefore, i ₃ ′=i ₃ +△i ₃ =i ₅ +i ₄ +i ₉ (11), and when the collector current i 5 of transistor Q ₅ is derived, _{i 5 =} i ₃ + △i ₃ − i ₄ −i ₉ ......(12). Here, since the control circuit 400 of this embodiment is implemented as a semiconductor integrated circuit, the transistor
Q ₂ and Q ₆ have the same characteristics, that is, they are affected by the same Early effect, their collector-emitter voltages are the same, and considering the condition of equation (8), △i ₃ = i ₉ becomes. Therefore, transistor Q ₅
The collector current i ₅ of is i ₅ = i ₃ − i ₄ (13), and the current fluctuation due to the Early effect of transistor Q ₂ does not appear. Therefore, the current ib is also constant, and the voltage drop across resistor _R6 is also constant, so
The voltage V _1-3 between terminals 1 and 3 is always a constant voltage without being affected by fluctuations in the power supply voltage.

Above, we have assumed the simplest conditions for convenience of explanation, but there are cases where the conditions deviate slightly from the ideal conditions, but even in this case, by considering the constants between each element and element matching, the optimal design can be achieved. is possible. Furthermore, when there is no fluctuation in the power supply voltage, the collector current i ₇ of the transistor Q ₆ is drawn by the transistor Q ₁₀ , so that the current i ₉ does not flow and does not interfere with the circuit operation.

In this way, in the control circuit of this embodiment, even if the power supply voltage fluctuates and the Early effect occurs in the transistor, causing the operating current to change, the current corresponding to the change is transferred to the current sources 6, 7 and the current mirror circuit 9. 9, a stable voltage is always supplied between terminals 1 and 3.

In the control circuit 400 of this embodiment shown in FIG. 2, the emitter and collector of another transistor are connected in series to the collector of the transistor Q ₂ of the constant current source 3, and the base of this transistor is used to generate a reference voltage. When connected to the output terminal d of the circuit 1, the collector-emitter voltage of the transistor _Q2 remains constant regardless of fluctuations in the power supply voltage, and its output current _i3 also remains constant without being affected by the Early effect. Then,
The voltage V _1-3 between terminals 1-3 also remains constant. However, the output circuit 5 is normally configured with a Darlington connection in order to supply sufficient load current to the load 200, or to generate a supply current or a slight current _i4 when the load fluctuates. Therefore, the minimum required power supply voltage Vcc in the case of the above circuit configuration is simply calculated as 2V _BE (base-emitter voltage) due to the Darlington configuration, and V of the transistor Q ₂ and the other transistor mentioned above. _CE (Collector)
The voltage is the sum of the voltage drop across the resistor R9 and the sum of the voltage drop across the resistor R9, resulting in a significant deterioration of the voltage reduction characteristics.

Therefore, according to the circuit configuration of this embodiment, since the circuit configuration of the constant current source 3 is the same as the conventional one, the voltage reduction characteristic in this part is the same as the conventional one. Further, in the constant current source 7 having no Early effect, the emitters and collectors of both transistors Q7 and Q8 are connected in series, and a diode D3 is connected to the collector of the transistor Q8.
Although the voltage between the collector and emitter of transistors Q7 and Q8 depends on the shape of the transistor, it is possible to operate at a voltage lower than the voltage between the base and emitter, and therefore, the voltage reduction characteristics are excellent.

An application example using the control circuit of this embodiment will be shown below.

First, FIG. 3 shows terminals 1 and 3 of the control circuit 400.
This is a case where a load 200 is connected between the two and used as a constant voltage source. A constant voltage source 250 between the terminal 1 and the (+) terminal of the control circuit 400 is connected to a second
It is the same as the reference voltage generating circuit 1 in the figure, and is shown as an external element for convenience, and the same applies to FIG. 4 as well. As already mentioned, the third
In the figure, the load is 200% regardless of fluctuations in the power supply voltage Vcc.
A constant voltage V _R is always obtained across the terminals of .

In FIG. 4, a transistor 50 is connected between terminals 1 and 3.
This is a case in which the base and emitter of 0 are connected through a resistor R1, and a load 200 is connected to the collector of the resistor R1 to form a constant current source. In such a configuration,
Even if the power supply voltage Vcc fluctuates, the transistor 500
The control circuit 40 of this embodiment is connected between the base and emitter of
Since the constant current i R is always kept constant by 0, a constant current i _R is supplied to the load 200 .

FIG. 6 shows an example of application in which the control circuit 400 of this embodiment controls the speed of a motor. Here, motor 300 is a DC motor. Before explaining this circuit configuration, a heater speed control circuit using a conventional control circuit 100 will be explained with reference to FIG.

Both FIG. 5 and FIG. 6 are bridge type current control type motor speed circuits. That is, the basic circuit configuration of the bridge type current control type is to connect both ends of the motor 300 to be controlled, which is a load, between the power supply voltage Vcc and the output terminal 3 of the control circuit 100, and to connect the terminal 1 of the control circuit 100 and the power supply. A configuration is adopted in which a resistor R2 is connected between Vcc and a variable resistor R3 for setting the target rotation speed is connected between terminal 1 and output terminal 3 of the control circuit 400. Further, in the bridge type current control type motor speed control circuit, the output circuit 5 has a current mirror configuration, and changes the current drawn from the terminals 3 and 1 according to the output signal of the comparator 2.

To explain the control principle, first, the voltage V _M at both ends of the DC motor during steady rotation is expressed by equation (14).

V _M =i _M・Ra+Ea……(14) i _M : Motor inflow current Ra: Motor internal resistance Ea: Induced voltage V _M : Motor terminal voltage Here, in order for the motor to rotate at a constant speed, the power supply voltage must be Even if Vcc fluctuates, the motor's induced voltage remains
It is sufficient to keep Ea constant.

However, in the bridge type current control type using the conventional control circuit 100, the motor terminal voltage V _M
is expressed as equation (15) because when the power supply voltage Vcc changes, the constant current i ₃ changes and a voltage of ΔV is generated between the two input terminals of the comparator amplifier 2.

V _M =i ₁・R ₂ +Vrefb+△V+i ₂ R ₂ (15) However, R2: Resistance value of resistor R ₂ Vrefb: Voltage generated in reference voltage generation circuit 1 △V: Early effect of transistor Q ₂ Also, i _M = i ₁₂ (i _M + i ₂ = i ₁₄ + i ₁₂ where i _M ≫ i ₂ , i ₁₂ ≫ i ₁₄
) i ₁ = i ₁₃ (i ₁ = i ₃ + i ₁₃ where i ₁₃ ≫i ₃ ).

Furthermore, in this bridge type current control type motor speed control circuit, when the load of the motor 300 fluctuates and the rotational speed tries to change, that is, when the induced voltage Ea of the motor 300 tries to change,
The output amplified by the comparator amplifier 2 according to the change is supplied to the output circuit 5, and the currents i ₁₂ and i ₁₃
is further drawn in to increase the current I _M supplied to the motor 300 to strengthen the rotational torque, thereby keeping the induced voltage Ea constant and the rotational speed constant. At this time, the relationship i _M +Ea=iR ₂ +Vref holds true. So motor 3
The induced voltage Ea of 00 is made to correspond to the output voltage Vref of the reference voltage generation circuit 1, and the value of the resistor _R2 is set to be the same value as the internal resistance Ra of the motor 300 or multiplied by a certain constant. Therefore, R ₂ =k·Ra and i _M =k·i ₁ hold true.

Under the above conditions, the first term in equation (15) is equal to the voltage drop i _M ·Ra of the motor internal resistance, and the second and subsequent terms correspond to the induced voltage Ea of the motor 300. That is, the induced voltage Ea of the motor 300
Since the corresponding term includes the change △V shown in equation (5) due to the Early effect of the transistor, the motor rotation speed has a dependence on the power supply voltage and has the characteristics shown in curve g in Figure 7. It was. On the other hand, in the bridge type current control type motor speed control circuit using the control circuit 400 according to the _present embodiment shown in FIG. Therefore, even if the power supply voltage fluctuates, the voltage in the control circuit 400 corresponding to the motor's induced voltage Ea does not change, and the motor rotation speed can be kept constant. A characteristic showing a constant rotation speed regardless of the power supply voltage as shown in Fig. 7h can be obtained.

As described above, the effects of the present invention are extremely large, and the fields of application are also very wide.

It should be noted that the present invention is not limited to the above embodiments, and various circuit modifications can be made within the scope of the invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a control circuit equipped with a conventional feedback amplifier circuit, FIG. 2 is a circuit diagram of a control circuit equipped with a feedback amplifier circuit according to an embodiment of the present invention, and FIG. 3 is a circuit diagram showing a control circuit equipped with a feedback amplifier circuit according to an embodiment of the present invention. Figure 4 is a block diagram of a constant voltage circuit constructed using the control circuit of this example, Figure 4 is a block diagram of a constant current source circuit constructed using the control circuit of this example, and Figure 5 is a conventional control circuit. A block diagram of a bridge type current control type motor speed control circuit constructed using the circuit, and Fig. 6 is a block diagram of a bridge type current control type motor speed control circuit constructed using the control circuit of this embodiment. 7 is a block diagram of the motor power supply voltage in the motor speed control circuit of FIGS. 5 and 6.
FIG. 3 is a characteristic diagram showing Vcc versus rotational speed. _R1 to _R15 ...Resistance, _D1 to _D3 ...Diode,
_Q1 to _Q10 ...Transistor.

Claims (1)

[Claims] 1 A comparator amplifier with a reference voltage applied to one input terminal and a negative feedback signal from the output circuit section applied to the other input terminal, and a load connected between the output terminal and the reference terminal, and a power supply terminal and the output. An emitter-collector path is connected between the point and the first
has a first transistor supplied with a bias voltage of as a load, amplifies the output from the load of the comparison amplifier, and supplies the amplified output as a drive signal to the output circuit section via the output point. a first current mirror circuit having an output end connected to the output point of the amplifier and a common end connected to the reference terminal; A second transistor having an emitter-collector path connected to the input end of the mirror circuit, and a common end having an output end connected to the input end of the first current mirror circuit were connected to the reference terminal. a second current mirror circuit, and respective emitters between the power supply terminal and the input terminal of the second current mirror circuit.
third and fourth transistors whose collector paths are connected in series, the first bias voltage is supplied to the bases of the second and third transistors, and the power supply terminal is connected to the base of the fourth transistor. A feedback amplifier circuit characterized in that the emitter-collector voltage of the third transistor is kept constant with respect to voltage fluctuations at the power supply terminal by supplying a second bias voltage that changes according to voltage fluctuations at the power supply terminal. .