Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-11-19
2003-02-25
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S901000, C323S908000
Reexamination Certificate
active
06525517
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power supply device such as a series regulator or a constant-voltage power supply, and to a semiconductor integrated circuit device constituting such a power supply device.
BACKGROUND ART
FIG. 6
shows a circuit diagram showing the internal configuration of a conventionally used power supply device. This conventional power supply device is composed of switches
1
and
2
, constant-current sources
3
,
4
, and
5
and a resistor R
1
to which a supply voltage Vcc is applied through the switch
2
, pnp-type transistors Tr
1
, Tr
2
, Tr
3
, Tr
6
, and Tr
8
, npn-type transistors Tr
4
, Tr
5
, and Tr
7
, an output terminal
6
, and resistors R
2
and R
3
for dividing the output voltage appearing at the output terminal
6
.
The transistor Tr
1
has its base connected to the switch
1
, has its emitter connected to the constant-current source
3
, and has its collector grounded. The transistors Tr
2
and Tr
3
have their emitters connected to the constant-current source
4
, have their bases connected respectively to the emitters of the transistors Tr
1
and Tr
6
, and have their collectors connected respectively to the collectors of the transistors Tr
4
and Tr
5
. The transistors Tr
4
and Tr
5
have their emitters grounded, and have their bases connected together. The transistor Tr
4
has its collector connected to its base, and the transistor Tr
5
has its collector connected to the base of the transistor Tr
7
.
The transistor Tr
6
has its emitter connected to the constant-current source
5
, has its base connected to the node between the resistors R
2
and R
3
, and has its collector grounded. The transistor Tr
7
has its collector connected to the resistor R
1
, and has its emitter grounded. The transistor Tr
8
receives at its emitter the supply voltage Vcc through the switch
2
, has its base connected to the resistor R
1
, and has its collector connected to the output terminal
6
. The resistor R
2
is connected to the output terminal
6
, and the resistor R
3
is grounded. When the switch
1
is switched to its contact “a,” the base of the transistor Tr
1
is grounded, and, when the switch
1
is switched to its contact “b,” a voltage VBG is applied to the base of the transistor Tr
1
. Furthermore, to the output terminal
6
, a capacitor Co is connected that provides phase compensation capacitance. The capacitor Co is grounded at the other end.
In this power supply device configured as described above, the constant-current sources
3
,
4
, and
5
and the transistors Tr
1
, Tr
2
, Tr
3
, Tr
4
, Tr
5
, and Tr
6
together constitute a comparator
11
, with the base of the transistor Tr
1
serving as a non-inverting input terminal, the base of the transistor Tr
6
serving as an inverting input terminal, and the node between the collectors of the transistors Tr
3
and Tr
5
serving as an output terminal. That is, the comparator
11
receives, at its non-inverting input terminal, the voltage VBG through the switch
1
and, at its inverting input terminal, a voltage obtained by dividing the output voltage appearing at the output terminal
6
with the resistors R
2
and R
3
, thereby forming a negative feedback circuit.
In this power supply device, when the switch
2
is closed, the supply voltage Vcc is applied to the constant-current sources
3
,
4
, and
5
, to the resistor R
1
, and to the emitter of the transistor Tr
8
. Simultaneously, the switch
1
is switched to its contact “b,” so that the input voltage VBG is applied to the base of the transistor Tr
1
. Making the base voltage of the transistor Tr
1
equal to VBG in this way brings the transistor Tr
1
into a non-conducting state. This reduces the current flowing from the base of the transistor Tr
2
to the emitter of the transistor Tr
1
, and thus makes the emitter current of the transistor Tr
3
larger than the emitter current of the transistor Tr
2
. On the other hand, the transistors Tr
4
and Tr
5
together constitute a current mirror circuit, and therefore the collector current s of the transistors Tr
4
and Tr
5
are equal to the emitter current of the transistor Tr
2
.
As a result, a current flows from the comparator
11
to the base of the transistor Tr
7
. This base current causes an amplified current to flow through the transistor Tr
7
as its collector current, and the resulting voltage drop across the resistor R
1
causes the base voltage of the transistor Tr
8
to drop. Thus, an emitter current starts flowing through the transistor Tr
8
, delivering an output voltage Vo to the output terminal
6
.
In this way, the power supply device configured as shown in
FIG. 6
outputs the output voltage Vo via its output terminal
6
. Here, the output voltage Vo takes several milliseconds to rise, and therefore a start-up charge current (hereinafter referred to as the “inrush current”) as large as 1 A or more flows through the capacitor Co. This inrush current flows to the limit of the current capacity of the output transistors of the power supply device, and therefore, in a case where the output current rises abruptly, as in the conventional power supply device under discussion, the heat accompanying the large inrush current may degrade the characteristics of, or even destroy, the power supply device. Moreover, for example, in a case where the source of the supply voltage Vcc is of a DC/DC type, the rush current causes a drop in the supply voltage Vcc, and is thus likely to cause start-up failure in all circuits that are used in parallel with the power supply device.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a power supply device provided with a soft starting function whereby the voltage that is fed in at start-up is increased gradually so that the output voltage rises gradually in order to reduce the inrush current at start-up.
To achieve the above object, according to claim
1
, a power supply device that controls an output voltage from an output circuit by comparing a monitoring voltage, which is obtained by dividing the output voltage, with a reference voltage by means of a comparator and keeping the monitoring voltage equal to the reference voltage on the basis of a comparison output from the comparator comprises a soft starting circuit that, at star-up, outputs a gradually increasing voltage and shuts off the reference voltage until the gradually increasing voltage reaches a predetermined voltage higher than the reference voltage.
In this power supply device, at the start-up thereof, the voltage output from the soft starting circuit increases gradually until it reaches the predetermined voltage, and, until this voltage output from the soft starting circuit reaches the redetermined voltage, the reference voltage fed to the comparator is shut off. This makes the voltage fed to the comparator vary gradually, and thereby suppresses the transient response of the output voltage from the output circuit at start-up.
REFERENCES:
patent: 4611154 (1986-09-01), Lambropoulos et al.
patent: 6188210 (2001-02-01), Tichauer et al.
patent: 6-163803 (1994-06-01), None
patent: 10-293617 (1998-11-01), None
Hiramatsu Yoshihisa
Hojo Yoshiyuki
Riley Shawn
Rohm & Co., Ltd.
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