Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-11-21
2004-04-20
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S224000, C323S284000
Reexamination Certificate
active
06724175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to power supply control devices, power supply circuits, power supply control methods, and electronic apparatuses. More particularly, the present invention relates to a power supply control device, a power supply circuit, a power supply control method, and an electronic apparatus, in which current to be supplied to a load is controlled by a transistor disposed between a power source and the load.
2. Description of the Related Art
In recent years, portable electronic apparatuses have been widespread. A portable electronic apparatus operates with a battery unit as its power source. Accordingly, the operating time of the apparatus by the battery unit is an important factor in measuring the performance of the apparatus. Such a portable electronic apparatus does not drive an internal circuit with the voltage of the battery unit. Therefore, a power supply circuit that converts the voltage of the battery unit into a voltage suitable for the internal circuit is contained in the apparatus.
It is preferable that the power consumption of the apparatus be reduced so as to prolong the operation time, while high efficiency is maintained in the power supply circuit. However, a high-efficient power supply circuit consumes a large amount of power.
Conventionally, synchronous DC-DC converters are used to improve the efficiency of a power supply circuit. As the performance of the CPUs contained in electronic apparatuses has been increased, the power consumption has been becoming larger. To restrict such an increase in power consumption, the voltage used in an electronic apparatus has been decreasing. As a result, the output of a DC-DC converter has become low-voltage, large-current output.
In view of this, it is essential to protect a DC-DC converter when short-circuiting or overloading occurs. Example methods of protecting a DC-DC converter from short-circuiting and overloading includes: a constant current control method in which the maximum value of the output current of the DC-DC converter is restricted through monitoring the output current; and an excess current preventing circuit method in which, the instant an excess current is detected, the DC-DC converter is stopped.
Generally, a current sense resistor is disposed in the output circuit of the DC-DC converter so as to monitor the voltage caused by the current flowing through such a current sense resistor. In a portable electronic apparatus, a battery unit is used as a power source for the internal devices. As a battery keeps discharging, the voltage of the battery normally drops. Therefore, DC-DC converters are employed to maintain the voltage used in an electronic apparatus at a constant value.
In a notebook-type computer, for instance, various devices such as a semiconductor device, a storage device, and a display device are mounted. These devices operate at different voltages from each other. More specifically, devices such as a HDD, CD-ROM, and DVD operate at 5.0 V, while a memory and a semiconductor device for controlling peripheral circuits operate at 3.3 V, for instance. As for the CPU, the operating voltage is 0.9 to 2.0 V.
Meanwhile, power is supplied to such a notebook-type computer from an external power source such as an AC adapter, or from a battery unit contained in the apparatus. In this case, a DC-DC converter is employed to produce various voltages required by the devices in the apparatus.
For such a DC-DC converter, a switching regulator type is widely used for its high efficiency. In a DC-DC converter of the switching regulator type, a transistor is disposed between a power source and a load, and this transistor is controlled so as to control the output voltage. To detect the current to be supplied to the load, a current sense resistor is connected in series between the transistor and the load. As the current to be supplied to the load flows through the current sense resistor, a voltage corresponding to the current is generated across the current sense resistor. By detecting this voltage generated across the current sense resistor, the current to be supplied to the load can be detected. Using the detected current, a control operation such as an excess current preventing operation is performed.
FIG. 1
is a block diagram of a power system of an electronic apparatus.
In a portable electronic apparatus
1
, such as a notebook computer, a commercial AC power supply
3
is converted into a DC power supply by an AC adapter
2
, and the DC power supply is generally used as the driving power. The conversion is externally carried out. The electronic apparatus
1
comprises a battery unit
5
, a charger
6
, diodes D
11
and D
12
, and DC-DC converters
7
-
1
to
7
-
3
. With this structure, the DC power from the AC adapter
2
is supplied to internal units
4
-
1
to
4
-
3
.
The battery unit
5
is used as the driving power when the electronic apparatus
1
is being carried. The charger
6
recharges the battery unit
5
with external power from the AC adapter
2
.
The diode D
11
prevents power supply from the battery unit
5
to the AC adapter
2
. The diode D
12
prevents direct voltage application from the AC adapter
2
to the battery unit while the AC adapter
2
is connected to the electronic apparatus
1
.
The DC-DC converter
7
-
1
converts DC voltage from the AC adapter
2
or the battery unit
5
into DC voltage demanded by the internal unit
4
-
1
, and then supplies the converted DC voltage to the internal unit
4
-
1
. The DC-DC converter
7
-
2
converts DC voltage from the AC adapter
2
or the battery unit
5
into DC voltage demanded by the internal unit
4
-
2
, and then supplies the converted DC voltage to the internal unit
4
-
2
. The DC-DC converter
7
-
3
converts DC voltage from the AC adapter
2
or the battery unit
5
into DC voltage demanded by the internal unit
4
-
3
, and then supplies the converted DC voltage to the internal unit
4
-
3
.
FIG. 2
is a block diagram of conventional DC-DC converters.
The DC-DC converters
7
-
1
to
7
-
3
each comprise a power supply control IC
10
, a main switching transistor Tr
1
, a synchronous rectifying transistor Tr
2
, diodes D
1
and D
2
, a choke coil L
1
, a smoothing capacitor C
1
, a back-flow preventing capacitor C
2
, and a current sense resistor R
1
.
An input voltage Vin is supplied to an input terminal Tin. The input terminal Tin is connected to the power supply terminal Tvin of the power supply control IC
10
and the drain of the main switching transistor Tr
1
.
The main switching transistor Tr
1
is constituted by an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the main switching transistor Tr
1
is connected to the input terminal Tin, while the source is connected to an output terminal Tout via the choke coil L
1
and the current sense resistor R
1
. The gate of the main switching transistor Tr
1
is connected to a terminal Tdh of the power supply control IC
10
. The main switching transistor Tr
1
is switched on and off, depending on a pulse supplied from the terminal Tdh of the power supply control IC
10
.
The output current of the main switching transistor Tr
1
is supplied to the choke coil L
1
. The choke coil L
1
, the synchronous commutating transistor Tr
2
, and the diode D
2
constitute a rectifier circuit that rectifies the pulse-type output current from the main switching transistor Tr
1
.
The anode of the diode D
1
is grounded, and the cathode of the diode D
1
is connected to the choke coil L
1
. The diode D
1
is a flywheel diode that supplies forward current to the choke coil L
1
when the main switching transistor Tr
1
is switched off, and is provided with reverse voltage and switched off when the main switching transistor Tr
1
is on.
The synchronous rectifying transistor Tr
2
is constituted by an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the synchronous rectifying transistor Tr
2
is connected to the source of the main switching transistor Tr
1
,
Itakura Kazuhiko
Matsuda Kouichi
Ozawa Hidekiyo
Takimoto Kyuichi
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