JPH0610412Y2 - DC constant voltage circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a DC constant voltage circuit, and in particular, even if the DC constant voltage circuit enters a non-stable region due to a decrease in input voltage The present invention relates to a DC constant voltage circuit that prevents current from increasing.

<Outline of the Invention> In the DC voltage regulator of the present invention, the output transistor has a current mirror configuration of three transistors, and the output transistor has three collectors, and the input voltage is lowered and the voltage regulator is unstable. When entering the unstable region by detecting the lowering of the third collector voltage from the first collector connected to the output terminal by the comparison circuit and controlling the output transistor by this detection output The drive current of the output transistor is prevented from increasing.

<Prior Art> FIG. 5 shows a conventional DC constant voltage circuit. The unstabilized power supply voltage Vi input to the input terminal Ti is the output transistor Q.
It is stabilized at the output terminal T0 via 1 and output as the output voltage V0. 1, 2 are constant current sources, 3 are differential amplifiers, Q
2 to Q6 are transistors, and ZD1 is a Zener diode. Q2 and Q3 form a current mirror, and Q5 and Q6 drive the output transistor Q1. The differential amplifier 3 has a reference voltage Vs generated by the Zener diode ZD1.
Is compared with a divided voltage obtained by dividing the output voltage V0 by R1 and R2, this is detected through a differential amplifier, and this output causes the output transistor Q via the transistors Q4 to Q6.
Control 1

Next, the operation of the circuit will be described with reference to the input characteristic diagram of FIG. As the input voltage Vi input to the power input terminal Ti rises, the output voltage V0 rises and the input voltage Vi rises.
Reaches 3.2 V, the output voltage V0 is constant at 3.0 V. On the other hand, the input current Ii input from the power source Vi rapidly increases with the increase of the input voltage Vi until the output voltage V0 enters the stable region and flows up to about 14 mA at maximum. On the contrary, when the power supply voltage Vi is lowered in the constant voltage state of the DC constant voltage circuit, the above is reversed and Vi is 3.2V.
The output voltage V0 begins to drop below this, but the input current Ii increases sharply and again when Vi drops below 3V.

In the stable region of the output voltage, the input current sharply rises due to the V supplied to the inverting input terminal of the differential amplifier 3.
Since the divided voltage of 0 becomes lower than the reference voltage Vs, the output of the differential amplifier 3 suddenly rises, which increases the base currents of the drive transistors Q5 and Q6 and causes current to flow in Q1, Q5 and Q6.

<Problems to be Solved by the Invention> In the above-described conventional example, when the power source Vi is turned on, a large drive current flows until the output voltage reaches the stable region. If a battery with a large internal impedance such as a lithium battery or a smoothing capacitor is used as the power supply, the power supply voltage will drop and it will not be possible to increase to the rated voltage of that battery. Therefore, there is a problem that constant voltage operation cannot be performed.

Further, in the case where the input voltage Vi is small and the difference with the output voltage is small, in the power supply in which the fluctuation of the input voltage is relatively large,
There is a problem that the input current Ii frequently increases and battery life is shortened.

An object of the present invention is to provide a DC constant voltage circuit that solves the above-mentioned various problems.

<Embodiment> FIGS. 1 to 3 are views for explaining a DC constant voltage circuit according to an embodiment of the present invention. FIG. 1 shows a specific circuit diagram of a DC constant voltage circuit, and the same parts as those in FIG. 5 are designated by the same reference numerals.

Q8 is an output transistor having a current mirror configuration, and its detailed connection diagram is shown in FIG. Transistors Q8A, Q8B
, And Q8C, and their emitters and bases are connected in common. The collectors are individually led out as terminals of C1, C2 and C3. Reference numeral 4 is a differential amplifier, and bases of Q9 and Q10 are commonly connected to form a current mirror circuit. Q7 represents a transistor connected in parallel with Q4.

The first collector C1 of the output transistor Q8 is the output terminal T
At 0, the second collector C2 is connected to the collector of the transistor Q10 and the third collector C3 is connected to the collector of the transistor Q9. The output of the differential amplifier 4 is Q7
Connected to the base of.

Next, the operation of the circuit will be described with reference to the characteristic diagrams of FIGS. When the input voltage Vi is sufficiently higher than the output voltage V0, the second and third collector currents I2 and I3 'of the output transistor Q8 and the transistor Q9 of the current mirror configuration are used.
Collector current I3 is set as follows.

In the following equation, I1 is the first collector current and k1 is the first and second collector currents.
, K2 indicates the shunt ratio of the collector current of the current mirror, and k2 indicates the shunt ratio of the current mirror constituted by Q9 and Q10.

Also, the third collector C3 current I of the output transistor Q8
3'is Is set so that Where I3 'and I3 are I
If 3 '> I3, the saturation region exists between the emitter of the output transistor Q8 and the third collector C3.

That is, the relationship between the third collector current I3 'and the collector current of the transistor Q9 is Becomes Therefore, k2 should be set to k2> 1.

Here, the voltage at the connection point B between the third collector C3 and the collector of the transistor Q9 is used to detect whether the first collector C1 has entered the saturation region. Therefore, if k2 is made too large, the detection accuracy decreases. . Therefore, usually 1.5 ~
It is set to about 3 (this is set with reference to the VCE-IC characteristic of FIG. 4).

Since the collector voltages of the first collector C1 and the second collector C2 are different, it is usually necessary to increase k2 by the amount that VCE of C2 is large.

Next, when the input voltage Vi decreases to about 3.3V and the first collector C1 approaches the saturation region, the current I1 of the first collector C1 decreases, but the second collector C2 still enters the saturation region. Since it does not exist, the decrease in the second collector current I2 is small. That is, if k1 which is the shunt ratio of the currents I1 and I2 of the first and second collectors C1 and C2 at this time is k1 ', k1
The relationship between 1 and k1 'is k1'<k1 (6).

Then, the input voltage Vi further decreases and becomes an input voltage substantially equal to 3.0 V of the output voltage V0, and the relation between the current I3 'of the third collector C3 and the collector current I3 of the transistor Q9 is I3'- When I3 ≦ 0 (6), the voltage at the point B becomes lower than the potential at the point A. Then, the output of the differential amplifier comparing the voltages at points A and B is lowered, which lowers the base potential of Q5 via the transistor Q7, which drives Q5 and Q6 driving the output transistor Q8. The current is limited.

The voltage between the collector and the emitter of the third collector C3 almost tracks the voltage between the collector and the emitter of the first collector C1, so that I3 'and I3 are Becomes Therefore, Becomes That is, k1 ' When k1 'is reduced up to, the input current Ii is limited and an extra current does not flow.

That is, when the input voltage Vi drops to around 3.0V, the sixth
As explained in the figure, the input current tries to increase rapidly, but since the increase of the drive current is suppressed by the above-mentioned operation, the transition is made as shown by the characteristic of the input current shown by the solid line in FIG.

<Effect of device> In the DC constant voltage circuit according to the present invention described above, when the power is turned on,
An excessive input current (drive current) does not flow until the predetermined regulated output voltage is reached.

As a result, when it is used as a power source with a large internal resistance, it can be started up promptly.

Further, when applied to a DC constant voltage circuit having a small difference between input and output voltages, it is possible to suppress an increase in input current even if the input voltage fluctuates and the voltage drops to around the output voltage.
In addition, this can reduce the decrease in the life of the battery when the battery is used as the power source.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a detailed circuit diagram of a DC constant voltage circuit according to an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of an output transistor Q8 in FIG. 1, and FIG. FIG. 4 is a characteristic diagram for explaining the operation of FIG. 1, FIG. 4 is a VCE-IC characteristic diagram of the transistor Q8, and FIG.
FIG. 6 is a circuit diagram of a conventional DC constant voltage circuit, and FIG. 6 is a characteristic diagram for explaining the operation of FIG. 1, 2 ... Constant current source, 3, 4 ... Differential amplifier (comparator), Q1-Q10 ... Transistor (Q8 ... Output transistor, Q9, Q10 ... Current mirror configuration), C1 ...
First collector, C2 ... Second collector, C3 ... Third
Collector, Ti ... input terminal, T0 ... output terminal.

Claims (1)

[Scope of utility model registration request] 1. In a DC constant voltage circuit for controlling an output transistor by the output of a differential amplifier for comparing a divided output voltage with a reference voltage, three transistors have their bases and emitters connected in common. The output transistor of the current mirror configuration having the first, second and third collectors, and the current flowing through the first, second and third collectors when the input voltage of the DC constant voltage circuit is higher than the output voltage. Is (However, I ₁ is the first collector current, I ₂ is the second collector current, I ₃ ′ is the third collector current, k ₁ is the shunt ratio of the first and second collector currents, and k ₁ is a number. The first collector is connected to the output terminal, the second collector terminal is connected to one transistor of the current mirror formed by a pair of transistors, and the third collector The collector terminal is connected to the other of the current mirror transistors, the first input end is connected to the first collector, and the second input end is connected to the connection point of the third collector and the other transistor. An output terminal connected to an input of a drive transistor for driving the output transistor,
And a differential amplifier for comparing the voltage input to the second input terminal, the third collector voltage when the DC constant voltage circuit plunges into the unstable region due to a decrease in the input voltage that is made constant. Is detected to be lower than the first collector voltage by the differential amplifier, and the detection output is used to control the output transistor.