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FIELD OF THE INVENTION
The present invention relates to a direct-current stabilizer including an
n-p-n transistor for controlling an output voltage.
BACKGROUND OF THE INVENTION
In general, a direct-current stabilizer is used to supply a DC voltage
necessary for electronic devices. For example, a so-called dropper-type
direct-current stabilizer which outputs a stabilized voltage by decreasing
an input voltage is commonly used because it has low noise and is easy to
design. The following description discusses such direct-current
stabilizers.
As illustrated in FIG. 19, in a direct-current stabilizer, for example,
when an input voltage applied to an input terminal IN reaches a
predetermined level, an actuator 81 starts operating and a reference
voltage circuit 82 generates a reference voltage. An output voltage
V.sub.O delivered to an output terminal OUT is divided by resistors
R.sub.81 and R.sub.82. The difference between the resulting voltage and
the reference voltage is amplified by a differential amplifier 83.
The differential amplifier 83 controls the base current of a transistor
Tr.sub.81 through a transistor Tr.sub.82 by adjusting an output according
to the difference. The transistor Tr.sub.81 is an n-p-n transistor for
controlling output, and stabilizes the output voltage V.sub.O by
controlling the base currents. The output voltage V.sub.O is applied to a
load 84. The output characteristics of the output voltage V.sub.O is
improved by a capacitor C.sub.81 connected to the output terminal OUT in
parallel with the load 84.
When the collector current of the transistor Tr.sub.81 is increased by a
short circuit or overload, the voltage drop in a resistor R.sub.83
connected to the emitter of the transistor Tr.sub.81 becomes significant.
Then, the base-emitter voltage of a transistor Tr.sub.83 for controlling
current is significantly increased. This causes the transistor Tr.sub.83
to be switched on, and the base currents of the transistors Tr.sub.82 and
Tr.sub.81 to be limited. Consequently, the collector current of the
transistor Tr.sub.81 is limited, and the transistor Tr.sub.81 is protected
from an overcurrent.
Another direct-current stabilizer shown in FIG. 20 includes a p-n-p
transistor Tr.sub.84 for controlling output. Similar to the
above-mentioned n-p-n transistor, with the p-n-p transistor Tr.sub.84, the
reference voltage circuit 82 generates a reference voltage with the
operation of the actuator 81, an output voltage is divided by the
resistors R.sub.81 and R.sub.82, and a difference between the divided
voltage and the reference voltage is amplified by the differential
amplifier 83. The base current of the transistor Tr.sub.84 is controlled
by the output of the differential amplifier 83 through a transistor
Tr.sub.85 as driver, and thereby stabilizing the output voltage V.sub.O.
When the collector current of the transistor Tr.sub.84 is increased by a
short circuit or overload, the collector current of the transistor
Tr.sub.85 is also increased. The base-emitter voltage of a transistor
Tr.sub.86 for controlling current is increased by a resistor R.sub.84
which is connected in series with the emitter of the transistor Tr.sub.85.
This causes the transistor Tr.sub.86 to be switched on, and the base
currents of the transistors Tr.sub.85 and Tr.sub.84 to be limited. As a
result, the collector Current of the transistor Tr.sub.84 is limited and
the transistor Tr.sub.84 is protected from an overcurrent.
However, since the former direct-current stabilizer uses the n-p-n
transistor Tr.sub.81 to control the output voltage, the collector-emitter
voltage drops significantly, causing considerable losses and poor
efficiency.
On the other hand, the latter direct-current stabilizer uses the p-n-p
transistor Tr.sub.84 for controlling the output voltage so as to reduce
the losses by minimizing the potential difference between the input
voltage and the output voltage. However, such a direct-current stabilizer
also has the following problem.
The p-n-p transistor usually can not produce a direct current gain that a
n-p-n transistor of the same chip size produces. Therefore, in order to
produce a direct current gain similar to the gain of the n-p-n transistor
of the same rating, it is necessary to increase the size of the chip,
resulting in an increase in costs.
Moreover, the direct-current stabilizer using a p-n-p transistor presents
the following structural problem.
A direct-current stabilizer shown in FIG. 21 has a structure where a
transistor section 91 as a transistor for controlling an output voltage
and an IC section 92 for controlling the transistor are vertically
arranged on a single chip. More specifically, such a direct-current
stabilizer has a Complicated structure where an n+ buried layer 94 and a
p.sup.+ buried layer 95 are formed in this order on a p-type substrate 93.
In addition, there is a need to provide a p-well region 96 to form the
p-n-p structure. Therefore, the number of wafer processes in manufacturing
is increased, resulting in an expensive chip. Furthermore, an increase in
the number of heat treatment processes causes the diffused layers 97
through 100 to expand, thereby increasing the area and costs of the chip.
A direct-current stabilizer shown in FIG. 22 has a structure where a
transistor section 101 as a transistor for controlling output voltage and
an IC section 102 for controlling the transistor are laterally arranged on
a single chip. In such a direct-current stabilizer, an emitter diffused
layer 104, a base diffused layer 105 and a collector diffused layer 106
are formed in a cross direction on an n-type epitaxial layer 103. This
arrangement causes the chip to have an increased area, resulting in an
increase in costs. The characters (B), (C) and (E) in the drawing
represent the base, collector and emitter, respectively.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a direct-current
stabilizer which uses an n-p-n transistor as a voltage control element and
operates with low losses.
In order to achieve the above object, an integrated direct-current
stabilizer of the present invention includes:
an n-p-n control transistor whose base current is controlled in accordance
with an output voltage of the direct-current stabilizer, for reducing an
input voltage and controlling the output voltage at a predetermined value;
an input terminal for receiving the input voltage; and
a first control terminal which is provided separately from the input
terminal and connected to the base of the control transistor for supplying
to the base of the control transistor a voltage which is not lower than
the sum of an emitter voltage and a base-emitter voltage.
In this direct-current stabilizer, when the voltage is applied to the first
control terminal, a voltage higher than the sum of the emitters voltage
and the base-emitter voltage is applied to the base of the control
transistor, thereby turning on the control transistor. Namely, the input
voltage is not used for activating the control transistor. Therefore,
there is no need to increase the potential difference between the input
voltage and the output voltage.
Thus, with the n-p-n control transistor, the losses of the direct-current
stabilizer are easily decreased. In addition, since the control transistor
is of an n-p-n type, the direct-current stabilizer is manufactured with
low costs.
In order to achieve the above object, another integrated direct-current
stabilizer of this invention includes:
an n-p-n control transistor for controlling an output voltage of the
direct-current stabilizer at a predetermined value by reducing an input
voltage;
an input terminal for receiving the input voltage;
a differential amplifier for controlling the base current of the control
transistor in accordance with the output voltage so that the control
transistor controls the output voltage at a predetermined value; and
a second control terminal which is provided separately from the input
terminal and connected to the source input of the differential amplifier
so as to apply to the base of the control transistor a voltage which is
not lower than the sum of the emitter voltage and the base-emitter
voltage.
In this direct-current stabilizer, when the voltage is applied to the
second control terminal, a voltage higher than the sum of the emitter
voltage and the base-emitter voltage is applied to the base of the control
transistor by the differential amplifier, and thereby turning on the
control transistor. Like the above-mentioned direct-current stabilizer,
with this structure, since there is no need to increase the potential
difference between the input voltage and the output voltage, a decrease in
the losses of the direct-current stabilizer is achieved with low costs.
This direct-current stabilizer further includes an n-p-n or p-n-p
transistor which forms a Darlington pair together with the control
transistor. The collector of the n-p-n transistor is connected to the
second control terminal, while the emitter of the p-n-p transistor is
connected to the second control terminal. This structure enables a
decrease in the losses of a direct-current stabilizer supplying high
output currents.
In order to achieve the above object, still another integrated
direct-current stabilizer of this invention includes:
an n-p-n control transistor whose base current is controlled in accordance
with an output voltage of the direct-current stabilizer, for reducing an
input voltage and controlling the output voltage at a predetermined value;
a driving circuit for driving the control transistor;
an input terminal for receiving the input voltage; and
a third control terminal which is provided separately from the input
terminal and connected to the source input of the driving circuit so as to
apply to the base of the control transistor a voltage which is not lower
than the sum of the emitter voltage and the base-emitter voltage.
In this direct-current stabilizer, when the voltage is applied to the third
control terminal, a voltage higher than the sum of the emitter voltage and
the base-emitter voltage is applied to the base of the control transistor
by the driving circuit, thereby turning on the control transistor. Like
the above-mentioned direct-current stabilizers, with this structure, since
there is no need to increase the potential difference between the input
voltage and the output voltage, a decrease in the losses of the
direct-current stabilizer is achieved with low costs.
All of the above-mentioned direct-current stabilizers further include a
current limiting means for limiting a flow of a current from the first,
second and third control terminals. Since the current limiting means
limits excessive currents from flowing from the first through third
control terminals, the consumption of power is limited.
Moreover, each of the first through third control terminals of these
direct-current stabilizers
(1) has a withstanding voltage which is higher than that of the input
terminal,
(2) is connectable to the input terminal, or connectable to the input
terminal if, for example, it is placed adjacent to the input terminal, and
(3) is connectable to an ON/OFF circuit for starting and stopping an
application of voltage.
The direct-current stabilizer having such characteristics brings the
following advantages (A) through (D).
(A) Since the withstanding voltage of the control terminal is higher than
that of the input terminal, it is possible to apply a voltage higher than
the input voltage to the control terminal without increasing the
withstanding voltages of other terminals including the input and output
terminals which require a change according to the input voltage. Namely,
the control transistor is driven by a voltage having a value different
from that of the input voltage.
(B) The input voltage is used for driving the control transistor by
connecting the control terminal to the input terminal. Since such a
direct-current stabilizer functions in the same manner as a convention
direct-current stabilizer using an n-p-n transistor, is used for various
purposes.
(C) The control terminal and the input terminal are easily connected to
each other by placing the control terminal adjacent to the input terminal.
(D) The output of these direct-current stabilizer is externally switched
between on and off by controlling the application of voltage to the
control terminal by means of the ON/OFF circuit.
For a fuller understanding of the nature and advantages of the invention,
reference should be made to the ensuing detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram schematically showing a structure of a
regulator IC according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a structure of a power source system
incorporating the regulator IC of FIG. 1.
FIG. 3(a) is a front view showing an internal structure of the regulator IC
of FIG. 1.
FIG. 3(b) is a side view showing an internal structure of the regulator IC
of FIG. 1.
FIG. 4 is a vertical section showing part of a structure of a transistor
chip and an IC chip in the regulator IC of FIG. 3.
FIG. 5 is a circuit diagram showing a structure of switching the output of
the regulator IC of FIG. 1.
FIG. 6 is a circuit diagram showing a structure of the regulator IC of FIG.
1, wherein a control terminal and an input terminal are connected.
FIG. 7 is a circuit diagram schematically showing a structure of a
regulator IC according to a second embodiment of the present invention.
FIG. 8 is a circuit diagram of a modified example of the regulator IC of
FIG. 7, having a Darlington pair of an n-p-n transistor and a control
transistor.
FIG. 9 is a circuit diagram of a modified example of the regulator IC of
FIG. 7, having Darlington pair of a p-n-p transistor and a control
transistor.
FIG. 10 is a circuit diagram schematically showing a structure of a
regulator IC according to a third embodiment of the present invention.
FIG. 11 is a circuit diagram showing the actuation of the regulator IC of
FIG. 10 with a control voltage as an example.
FIG. 12 is a circuit diagram showing switching off the output of the
regulator IC of FIG. 10 as an example.
FIG. 13 is a circuit diagram showing the actuation of the regulator IC of
FIG. 10 with an input voltage as an example.
FIG. 14 is a circuit diagram of a modified regulator IC of FIG. 10, wherein
a current limiter is placed in a position located between a control
terminal and a differential amplifier and between the control terminal and
a driving circuit.
FIG. 15 is a circuit diagram of a modified regulator IC of FIG. 10, wherein
a current limiter is placed between a control terminal and a differential
amplifier.
FIG. 16 is a circuit diagram of a modified regulator IC of FIG. 10, wherein
a current limiter is placed between a control terminal and a driving
circuit.
FIG. 17 is a circuit diagram schematically showing a structure of a
regulator IC according to a fourth embodiment of the present invention.
FIG. 18(a) is a front view showing an internal structure of the regulator
IC of FIG. 17.
FIG. 18(b) is a side view showing an internal structure of the regulator IC
of FIG. 17.
FIG. 19 is a circuit diagram showing a structure of a conventional
direct-current stabilizer using an n-p-n control transistor..
FIG. 20 is a circuit diagram showing a structure of a conventional
direct-current stabilizer using a p-n-p control transistor.
FIG. 21 is a vertical section showing a structure of a vertically
constructed chip of a conventional direct-current stabilizer using a p-n-p
control transistor.
FIG. 22 is a vertical section showing a structure of a laterally
constructed chip of a conventional direct-current stabilizer using a p-n-p
control transistor.
DESCRIPTION OF THE EMBODIMENTS
[EMBODIMENT 1]
The following description discusses a first embodiment of the present
invention with reference to FIGS. 1 through 6.
As illustrated in FIG. 2, a power source system of this embodiment includes
a line filter 1, a bridge rectifier 2, a control IC 3 for controlling
switching, a photocoupler 4 for insulation, and a regulator IC 5 as a
direct-current stabilizer. The power source system also has a transistor
Tr.sub.1 for switching, a high frequency transformer T, a transistor
Tr.sub.2 for controlling ON/OFF switching, smoothing capacitors C.sub.1 to
C.sub.3, diodes D.sub.1 and D.sub.2 as rectifiers, and a resistor R.sub.1.
In this power source system, line noise is removed from a 100 V alternating
current by the line filter, and the resulting alternating current is
rectified and smoothed by the bridge rectifier 2 and the capacitor C.sub.1
to produce a DC voltage. The DC voltage is changed into pulse form when
the transistor Tr.sub.1 is switched between on and off by the control IC
3. The voltage pulses thus obtained are transmitted through the high
frequency transformer T toward the outputs, and rectified and smoothed by
a circuit formed by a diode D.sub.1 and a capacitor C.sub.2 and a circuit
formed by a diode D.sub.2 and a capacitor C.sub.3, respectively, to
produce two DC voltages.
The DC voltage output from the diode D.sub.1 is fed back as an output
voltage V.sub.O.sbsb.1 through the photocoupler 4 to the control IC 3. The
output voltage V.sub.O.sbsb.1 also goes through the resistor R.sub.1 and
is input to a control terminal CNT.sub.1 of the regulator IC 5. On the
other hand, the DC voltage output from the diode D.sub.2 is input to the
input terminal IN of the regulator IC 5.
In the regulator IC 5, an input voltage supplied to the input terminal IN
from the diode D.sub.2 is controlled by driving a transistor Tr.sub.3, to
be described later (see FIG. 1), with the output voltage V.sub.O.sbsb.1,
and a stabilized output voltage V.sub.O.sbsb.2 is produced. The output of
the regulator IC 5 is switched between on and off by starting or stopping
application of voltage to the transistor Tr.sub.3. The application of the
voltage is started or stopped by switching the transistor Tr.sub.2 as an
ON/OFF circuit between on and off in accordance with an ON/OFF control
signal supplied from an external source.
As illustrated in FIG. 1, the regulator IC 5 includes the input terminal IN
connected to an external device, an output terminal OUT, a ground terminal
GND, and the control terminal CNT.sub.1. The regulator IC 5 also includes
the transistor Tr.sub.3, resistors R.sub.2 through R.sub.4, a differential
amplifier 6 and a reference voltage circuit 7 as essential components for
the direct-current stabilizer.
The base of the transistor Tr.sub.3 as an n-p-n control transistor is
connected to the output terminal of the differential amplifier 6, and
connected through the resistor R.sub.2 to the control terminal CNT.sub.1
as a first control terminal. The collector of the transistor Tr.sub.3 is
connected to the input terminal IN, while the emitter thereof is connected
to the output terminal OUT. The withstanding voltage of the control
terminal CNT.sub.1 is higher than those of other terminals IN, OUT and
GND. Therefore, for example, the control terminal CNT.sub.1 has an
insulating layer with a thickness greater than those of the insulating
layers on other terminals, IN, OUT and GND.
Placed between the output terminal OUT and the ground terminal GND are the
resistors R.sub.3 and R.sub.4 which are connected in series and form a
voltage divider. The junction between the resistor R.sub.3 and R.sub.4 is
connected to the negative input of the differential amplifier 6.
The reference voltage circuit 7 is placed between the input terminal IN and
the ground terminal GND. The reference voltage circuit 7 is a circuit for
generating a predetermined reference voltage according to the input
voltage. For example, a fixed voltage element such as a Zener diode, and a
fixed voltage circuit are used as the reference voltage circuit 7. The
reference voltage circuit 7 is connected to the positive input of the
differential amplifier 6 and supplies a predetermined voltage thereto.
The positive source input of the differential amplifier 6 is connected to
the input terminal IN, while the negative source input thereof is
connected to the ground terminal GND. The differential amplifier 6
controls the emitter voltage or the output voltage of the regulator IC 5
by controlling the base current of the transistor Tr.sub.3, so that the
feedback voltage divided by the resistors R.sub.3 and R.sub.4 becomes
equal to the reference voltage of the reference voltage circuit 7.
In the regulator IC 5, a current limiter 8 as current limiting means is
placed between the control terminal CNT.sub.1 and the resistor R.sub.2.
The current limiter 8 limits an increase in the power consumption by
limiting the current flowing from the control terminal CNT.sub.1 to the
base of the transistor Tr.sub.3 to a predetermined value.
The regulator IC 5 with such a circuit structure includes a transistor
section 9 and an IC section 10 manufactured as a single chip as shown in
FIGS. 3(a) and 3(b). The transistor section 9 is the transistor Tr.sub.3
produced in chip form. The IC section 10 is formed by integrating on a
single chip all the above-mentioned elements and circuits, except for the
transistor Tr.sub.3. The transistor section 9 and the IC section 10 are
die-bonded onto a multi-lead metal frame 12 at a junction 11 of a solder.
A near central portion of one edge of the metal frame 12 is elongated to
form an outer lead flame 13 as the ground terminal GND. In FIGS. 3(a) and
3(b), an outer lead frame 14 as the output terminal OUT is formed in
parallel with and on the left side of the outer lead frame 13, while an
outer lead frame 15 as the input terminal IN and an outer lead frame 16 as
the control terminal CNT.sub.1 are formed in parallel with and on the
right side of the outer lead frame 13. The metal flame 12 is fixed to an
inner lead flame 17.
A contact section 9a of the transistor section 9, which functions as a
collector, is connected to the outer lead frame 15, and a contact section
9b thereof functioning as an emitter is connected to the outer lead frame
14. A contact section 10a of the IC section 10 to be grounded is connected
to the metal frame 12, and a contact section 10b thereof to which a
control signal is input is connected to the outer lead frame 16. These
connections are made by wire bonds using metal wires 18.
The chips 9 and 10, the metal flame 12 and the inner lead frame 17 as well
as one end of each of the outer lead frames 13 through 16 are covered with
a package 19. The package 19 is made from a coating resin, such as an
epoxy resin, and formed by transfer-molding for example.
The sectional structure of the transistor section 9 and the IC section 10
is discussed below.
As illustrated in FIG. 4, in the transistor section 9, an n+ buried layer
21 and an n-type epitaxial layer 22 as the collector are formed on a
p-type substrate 20. Further, a base diffused layer 23, an emitter
diffused layer 24 and a collector layer 25 are formed on the epitaxial
layer 22.
The IC section 10 has a portion where a base diffused layer 27, an emitter
diffused layer 28 and a collector layer 29 are formed on an n+ buried
layer 26 and the n-type epitaxial layer 22 over the p-type substrate 20.
The epitaxial layer 22 includes isolation diffused layers 30 through 33 so
as to separate the transistor section 9 and the IC section 10 from each
other.
The operation of the regulator IC 5 of such a structure is discussed below.
As illustrated in FIGS. 2 and 5, a control voltage V.sub.C derived from an
output voltage V.sub.O.sbsb.1 is applied through the resistor R.sub.1 to
the control terminal CNT.sub.1. When the transistor Tr.sub.2 is switched
off, the control voltage V.sub.C is applied to the control terminal
CNT.sub.1. On the other hand, when the transistor Tr.sub.2 is switched on,
no control voltage V.sub.C is applied to the control terminal CNT.sub.1.
The value of the control voltage V.sub.C is set so that a voltage, which is
not lower than the sum of the emitter voltage of the transistor Tr.sub.3,
i.e., the output voltage V.sub.O (V.sub.O.sbsb.2) of the regulator IC 5
and the base-emitter voltage, is applied to the base of the transistor
Tr.sub.3. In the case when the output voltage V.sub.O of the regulator IC
5 is 5 volts, the control voltage V.sub.C is set to a value which meets
the requirement, for example, around 10 volts.
When the transistor Tr.sub.2 is switched off and the control voltage
V.sub.C is applied to the control terminal CNT.sub.1, the transistor
Tr.sub.3 is biased and switched on. At this time, the output voltage
V.sub.O appearing at the emitter is divided by the resistors R.sub.3 and
R.sub.4 to produce a feed back voltage. The feed back voltage is applied
to the differential amplifier 6, and the reference voltage generated by
the reference voltage circuit 7 is also applied thereto. The differential
amplifier 6 controls the base current of the transistor Tr.sub.3 according
to the difference between the feedback voltage and the reference voltage.
Thus, the transistor Tr.sub.1 controls an input voltage V.sub.IN so as to
produce the output voltage V.sub.O of a value which is determined by the
dividing rate of the resistors R.sub.3 and R.sub.4 and by the reference
voltage.
When the transistor Tr.sub.2 is switched on by an ON/OFF control signal, no
control voltage V.sub.C is applied to the control terminal CNT.sub.1,
thereby switching off the transistor Tr.sub.3. This causes the output of
the regulator IC 5 to be switched off. Namely, the output of the regulator
IC 5 is switched between on and off by switching the transistor Tr.sub.2
between on and off.
As described above, in the regulator IC 5, the transistor Tr.sub.3 is
activated upon the application of the control voltage of a predetermined
value to the control terminal CNT.sub.1. Unlike a regulator IC which uses
the input voltage V.sub.IN to drive the transistor Tr.sub.3, the regulator
IC 5 does not require a high input voltage V.sub.IN. For example, when the
output voltage V.sub.O is 5 volt, the input voltage V.sub.IN is set to
around 5.5 volt in anticipation of a lowering of the collector-emitter
voltage of the transistor Tr.sub.3.
It is therefore possible to reduce the losses of the regulator IC 5 to a
large degree. Moreover, since the n-p-n transistor Tr.sub.3 which has a
smaller chip size and is inexpensive to manufacture is used, the low-cost
regulator IC 5 is obtained.
Furthermore, since the regulator IC 5 includes the current limiter 8 for
limiting a current delivered from the control terminal CNT.sub.1, it is
possible to restrict the power consumption of the regulator IC 5.
Since the withstanding voltage of the control terminal CNT.sub.1 is higher
than those of other terminals IN, OUT and GND, the regulator IC 5 is
protected from the control voltage V.sub.C. In addition, it is possible to
switch the output of the regulator IC 5 between on and off by connecting
the transistor Tr.sub.2 to the control terminal CNT.sub.1.
In the regulator IC 5 since the input terminal IN and the control terminal
CNT.sub.1 are located adjacent to each other as shown in FIG. 3, the input
terminal IN and the control terminal CNT.sub.1 are easily connected as
shown in FIG. 6. With this arrangement, since the input voltage V.sub.IN
is applied to the control terminal CNT.sub.1, the transistor Tr.sub.3 is
driven by the input voltage V.sub.IN like in a conventional regulator IC.
Namely, the regulator IC 5 is used even in a power source system with a
single output.
Consequently, by providing the control terminal CNT.sub.1, the low-cost
general-purpose regulator IC 5 achieving a reduction in the losses is
obtained.
[EMBODIMENT 2]
The following description discusses a second embodiment of the present
invention with reference to FIGS. 7 through 9. The components having the
same function as the components described in the first embodiment will be
designated by the same code and their description will be omitted.
A direct-current stabilizer of this embodiment is shown in FIG. 7 as a
regulator IC 41 having a control terminal CNT.sub.2.
The withstanding voltage of the control terminal CNT.sub.2 as a second
control terminal is higher than those of other terminals IN, OUT, and GND.
The control terminal CNT.sub.2 is connected through the current limiter 8
to the positive source input of the differential amplifier 6. The control
terminal CNT.sub.2 is connectable to a transistor, not shown, like the
transistor Tr.sub.2 in the first embodiment (see FIG. 5). Connecting the
control terminal CNT.sub.2 to the transistor allows the output of the
regulator IC 41 to be switched between on and off. In an actual IC
package, the control terminal CNT.sub.2 is located adjacent to the input
terminal IN.
The operation of the regulator IC 41 having such a structure is discussed
below.
In the regulator IC 41, the control voltage V.sub.C is applied to the
control terminal CNT.sub.2. The effective variations in the output voltage
of the differential amplifier 6 are determined by the power source
voltage, i.e., the control voltage V.sub.C. Namely, the value of the
control voltage V.sub.C is set such that the differential amplifier 6
applies to the base of the transistor Tr.sub.3 a voltage not lower than
the sum of the emitter voltage and the base-emitter voltage.
When the control voltage V.sub.C is applied to the control terminal
CNT.sub.2, the transistor Tr.sub.3 is biased and switched on, so that the
output voltage V.sub.O is delivered to the output terminal OUT. Then, the
base current of the transistor Tr.sub.3 is controlled by the differential
amplifier 6 according to the feedback voltage produced by dividing the
output voltage V.sub.O with the resistors R.sub.3 and R.sub.4 and the
reference voltage of the reference voltage circuit 7. Consequently, the
transistor Tr.sub.3 controls the input voltage V.sub.IN to produce the
output voltage V.sub.O of a constant value which is determined by the
dividing rate of the resistors R.sub.3 and R.sub.4 and the reference
voltage.
As described above, in this embodiment, since the control voltage V.sub.C
of value different from that of the input voltage V.sub.IN is used as a
power source for the differential amplifier 6, the low-cost regulator IC
41 having reduced losses like the above-mentioned regulator IC 5 is
obtained.
Modified examples of the regulator IC 41 are shown as regulators IC 42 and
43 in FIGS. 8 and 9.
The regulator IC 42 includes an n-p-n transistor Tr.sub.4. The emitter of
the transistor Tr.sub.4 is connected to the base of the transistor
Tr.sub.3, forming a Darlington pair. The collector of the transistor
Tr.sub.4 is connected to the control terminal CNT.sub.2 and the base
thereof is connected to the output terminal of the differential amplifier
6.
Since the transistors Tr.sub.3 and Tr.sub.4 of the regulator IC 42 form a
Darlington pair, the regulator IC 42 is capable of supplying an output
current greater than that of the regulator IC 41. However, the voltage
necessary for driving the transistor Tr.sub.3 includes the base-emitter
voltage of the transistor Tr.sub.4. Therefore, the base-emitter voltage
must be considered when determining the value of the control voltage
V.sub.C.
On the other hand, the regulator IC 43 includes a p-n-p transistor Tr.sub.5
instead of the transistor Tr.sub.4. The transistors Tr.sub.3 and Tr.sub.5
form a Darlington pair. Since the transistor Tr.sub.5 is a p-n-p
transistor, the regulator IC 43 is designed so that the differential
amplifier 6 draws a current from the base of the transistor Tr.sub.5.
Namely, the positive input of the differential amplifier 6 is connected to
the junction of the resistors R.sub.3 and R.sub.4, and the negative input
is connected to the output of the reference vo | | |
