JPH0124645Y2 - - Google Patents

Description

[Detailed Description of the Invention] A constant voltage circuit generally compares its output voltage with a reference voltage, and stabilizes its output voltage using the comparison output.

Figure 1 shows an example of such a constant voltage circuit, where T ₁ is an input terminal to which an unregulated DC voltage is supplied, and T ₂ is an output terminal from which a stabilized output voltage is taken out. . And Q ₁ ~ Q ₄
indicates a transistor for forming a reference voltage, and transistors Q ₁ and Q ₂ constitute a feedback circuit. The collector of transistor Q ₁ is connected to terminal T 1 through resistor R ₁ , and its emitter is connected to terminal T ₁ through resistor R 1. grounded, the base of transistor Q ₂ is connected to the collector of transistor Q ₁ , its emitter is connected to the base of transistor Q ₁ , and
It is grounded through the resistor R ₂ , the collector of which is connected to the collector of the transistor Q ₃ .

This transistor Q ₃ constitutes a current mirror circuit together with a transistor Q ₄ with this as the input side. The collector of the transistor Q ₃ is connected to the bases of the transistors Q ₃ and Q ₄ , and their emitters are connected to the terminal T. ₁ and the collector of transistor Q ₄ is grounded through resistor R ₃ .

Moreover, Q ₅ and Q ₆ indicate transistors for comparing the reference voltage and the output voltage. These transistors Q ₅ and Q ₆ are configured as a differential amplifier, and their emitters are grounded through a resistor R ₄ , the base of transistor Q 5 is connected to the collector of transistor Q 4 , and the base of transistor Q ₅ is connected to the collector of transistor Q _{4 .} The collector of is connected to the terminal T ₁ through the resistor R ₅ ,
Transistor Q ₆ is diode connected and
Its base and collector are connected to terminal _T2 .

Furthermore, Q ₇ indicates a transistor that controls the output voltage constant based on the comparison output, its emitter is connected to the terminal T ₁ , its collector is connected to the terminal T ₂ , and its base is connected to the collector of the transistor Q ₅ . Connected.

Therefore, when the base potential of transistor Q ₁ increases, for example, its collector current increases and the base potential of transistor Q ₂ decreases, and since its collector current decreases, the base potential of transistor Q ₁ decreases, i.e. , since negative feedback is applied to the transistor Q ₁ through the transistor Q ₂ , the base potential of the transistor Q ₁ becomes constant.

If the base-emitter voltage of the transistors _Q1 to _Q7 is _VBE , and the base current is ignored, the current _I2 flowing through the resistor _R2 becomes _I2 = _VBE / _R2 . This current I ₂ is also the collector current of the transistor Q ₂ , and is also the collector current of the transistor Q ₃ ,
Since Q ₄ constitutes a current mirror circuit,
The collector current I ₄ of the transistor Q ₄ is I ₄ =I ₂ . Therefore, the voltage drop Vr occurring across resistor _R3
is Vr=I ₄ ·R ₃ =V _BE ·R ₃ /R ₂ , which is a constant level.

Therefore, the reference voltage Vr is obtained at the resistor _R3 , and this voltage Vr is supplied to the transistor _Q5 .

Then, in transistors Q ₅ and Q ₆ , the reference voltage Vr and the output voltage are compared, and when the output voltage increases, for example, the collector current of transistor Q ₅ decreases, and the impedance between the collector and emitter of transistor Q ₇ increases. As a result, the output voltage decreases, and when the output voltage decreases, the collector current of transistor _Q5 increases, so the impedance of transistor _Q7 decreases, and the output voltage increases. Therefore, the output voltage is the voltage
It is stabilized at a constant value based on Vr.

In this case, according to this circuit, if the collector-emitter voltage of transistor Q ₂ is V _CE , the input voltage from transistors Q ₁ to _{Q 3} will be 2V _BE + V _CE 1.5 to 1.7 [V] or higher. This is advantageous in battery operated sets. In addition, it is easy to integrate it into an IC.

However, in this circuit, if the collector current of transistor Q ₁ is I ₁ , its change is ΔI ₁ , and the change between its base and emitter is ΔV _BE , then ΔV _BE 26ln (1 + ΔI ₁ /I ₁ ) [mV] In addition, the current I ₁ changes in accordance with the input voltage, so when the input voltage changes, the reference voltage Vr changes, and therefore the output voltage also changes.

Therefore, as shown in Figure 2, a transistor
It is conceivable that Q ₃ and Q ₄ also constitute a feedback circuit in the same way as transistors Q ₁ and Q ₂ , and that they are continuously connected.

In this way, the current I ₄ flowing through the resistor R ₄
Since Vr is stabilized in two stages, the reference voltage Vr becomes sufficiently stable, and therefore the output voltage also becomes sufficiently stable.

But in this circuit, transistors Q ₁ to _{Q 4}
Therefore, the input voltage needs to be 3V _BE +V _CE 2.2 to 2.4 [V] or higher, which is disadvantageous for a battery-operated set.

Further, as shown in FIG. 3, transistors Q ₃ ,
It is also conceivable to configure a feedback circuit using Q ₄ and to configure a current mirror circuit using transistors Q ₁₁ , Q ₁₂ and Q ₁₃ , Q ₁₄ to form the reference voltage Vr.

In this way, the reference voltage Vr becomes sufficiently stable and the output voltage also becomes sufficiently stable, similar to the circuit shown in FIG. Moreover, the input voltage only needs to be 2V _BE +V _CE 1.5 to 1.7 [V] or more.

However, this circuit has a large number of parts and the IC
However, I don't like it.

This invention aims to provide a reference voltage forming circuit that eliminates the above problems.

Let's explain one example below.

In the example shown in FIG. 4, transistor Q ₁
˜Q ₇ and resistors R ₁ to R ₅ are connected in the same way as in the circuit of FIG. 1, and a transistor Q ₈ is provided, the base of which is connected to the base of transistor Q ₁ and the collector of which is ₄ and its emitter is grounded through resistor _R6 .

According to this configuration, the base potential of transistor Q ₂ is 2V _BE , so the input voltage is reduced to V ₁
Then, the collector current I ₁ of transistor Q ₁ is I ₁ =(V ₁ −2V _BE )/R ₁ , which is shown as curve I ₁ in FIG.

In addition, the collector current I ₂ of the transistor Q ₂ is I ₂ =V _BE /R ₂ , and since the transistors Q ₃ and Q ₄ constitute a current mirror circuit, the collector current I ₄ of the transistor Q ₄ is also I ₄ =V _BE /R ₂ , which is shown in FIG. 5 as curve I ₄ .
Note that this current I ₄ is the current in the circuit shown in Figure 1.
Exactly the same as I ₄ .

Furthermore, if R ₆ = 0, transistors Q ₁ and Q ₈ are supplied with the same base bias, so the collector current I ₈ of transistor Q ₈ at this time matches the collector current I ₁ , and this is shown by curve I ₁ in FIG. But in reality, R ₆ ≠0
So, the base bias of transistor _Q8 is
Compared to the base bias of transistor Q ₁ , it is smaller by a value corresponding to resistor R ₆ , and therefore the collector current I ₈ of transistor Q ₈ is smaller than the collector current I ₁ as shown as curve I ₈ in FIG. resistor compared
It becomes smaller at a rate corresponding to R ₆ . and,
In this case, by setting the resistor R ₆ to a predetermined value Rr, the curve I ₈ is changed to the curve I ₄ as shown in FIG.
can be made almost parallel to

Since the emitters of transistors Q ₄ and Q ₈ are grounded, they act as constant current sources and have a large output impedance. Therefore,
Resistor R ₃ has a current of the difference between currents I ₄ and I ₈ (I ₄ − _{I 8} )
flows, and since the curves I ₄ and I ₈ are almost parallel, the current (I ₄ - I ₈ ) is almost parallel to the horizontal axis as shown in Figure 5, that is, the input voltage V ₁ Even if the current (I ₄ −I 8 ) changes, the current (I 4 −I ₈ ) remains almost constant.

Therefore, a constant reference voltage Vr is obtained at the resistor _R3 regardless of the input voltage _V1 , so that the output voltage is also stabilized to a constant value even if the input voltage changes.

Thus, according to this invention, an extremely stable reference voltage Vr can be obtained even if the input voltage _V1 fluctuates. That is, when the transistor Q ₈ and the resistor R ₆ are not connected (in the case of the circuit shown in Fig. 1), the current I ₄ flows through the resistor R ₃ to form the reference voltage Vr, and this current As shown in Figure 5, I ₄ changes relatively significantly with respect to changes in input voltage V ₁ , so reference voltage Vr also changes due to input voltage V 1.
It changes relatively significantly with respect to changes in V ₁ .

However, in this idea, the transistor
Since we connect Q ₈ and resistor R ₆ , the current (I ₄
−I ₈ ) flows through resistor R ₃ to form the reference voltage Vr. At this time, since the current (I ₄ −I ₈ ) is extremely stable with respect to changes in the input voltage V ₁ , the reference voltage Vr also changes to the input voltage Vr. It becomes extremely stable against changes in V ₁ .

In addition, the input voltage V ₁ only needs to be 2V _BE +V _CE = 1.5 to 1.7 [V] or more, that is, the minimum required voltage is small, so it is suitable for a battery-operated set. Further, compared to the circuit shown in FIG. 1, the number of components is reduced by only increasing the transistor Q ₈ and the resistor R ₆ , which is advantageous when integrated into an IC.

FIG. 6 shows another example of this invention, in which the collector and base of transistor Q ₁ are connected to the base of transistor Q ₈ , and a resistor
The collector and emitter of a transistor Q9 are connected between _R1 and the collector of the transistor _Q1 , and _the collector and base of the transistor _Q9 are connected to the base of the transistor _Q2 .

Therefore, the base potential of the transistor Q ₂ becomes 2V _BE due to the transistors Q ₉ and Q ₁ , so the emitter potential of the transistor Q ₂ becomes V _BE . Therefore, since the collector current I ₂ of the transistor Q ₂ becomes I ₂ =V _BE /R ₂ , the collector current I ₄ of the transistor Q ₄ also becomes I ₄ =V _BE /R ₂ , which is also the fifth It is shown by curve I ₄ in the figure.

And the collector current I ₈ of transistor Q ₈ is
As shown by the curve I ₈ in FIG. 5, a current (I ₄ −I ₈ ) flows through the resistor R ₃ and a constant reference voltage Vr is obtained.

In addition, in the above, if a diode is connected in series with the resistor R ₃ or in place of the resistor R ₃ ,
The reference voltage Vr can be made more stable.

[Brief explanation of the drawing]

Figures 1 to 3 are connection diagrams for explaining this invention, Figure 4 is a connection diagram of an example of this invention, Figure 5 is a diagram for explaining it, and Figure 6 is another example of this invention. FIG. 3 is an example connection diagram. _T1 is an input terminal, _T2 is an output terminal, and _Q1 to _Q9 are transistors.

Claims (1)

[Scope of utility model registration request] A first transistor to which a predetermined voltage is supplied and a base-emitter voltage is taken out based on this supplied voltage, a resistor to which the base-emitter voltage of this first transistor is supplied, and a current flowing through this resistor. a third transistor that obtains a collector current corresponding to the current flowing through the resistor by the output of the second transistor; and a base-emitter voltage extracted by the first transistor. is supplied to its base, and a resistor is connected to its emitter, and by setting the value of the other resistor to a predetermined value with respect to the value of the one resistor, the third transistor is A reference voltage forming circuit that removes dependence of a difference current between a collector current of a transistor and a collector current of the fourth transistor on a change in the supply voltage to obtain a reference voltage based on the difference current.