DC-DC converter and semicondutor integrated circuit device...

Details DC-DC converter and semicondutor integrated circuit device... DC-DC converter and semicondutor integrated circuit device...

2001-01-26

2002-01-08

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C320S140000

Reexamination Certificate

active

06337563

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a DC—DC converter and a semiconductor integrated circuit device for a DC—DC converter, and, more particularly, to a DC—DC converter which is used as a power supply for a portable electronic apparatus.
A DC—DC converter is installed in a portable electronic apparatus, such as a notebook type personal computer. The DC—DC converter supplies DC power, supplied from an external AC adapter, to internal circuits of an electronic apparatus and charges a battery equipped as an auxiliary power supply.
To operate the AC adapter stably and safely, the DC—DC converter is designed in such a way that the sum of the current consumed by the internal circuits and the charge current of the battery becomes smaller than the current supplying capacity of the AC adapter. When AC adapters of different current supplying capacities are to be used, it is necessary to use the current supplying capacity of each AC adapter to the full.
FIG. 1
is a schematic circuit diagram of a DC—DC converter
1
according to first prior art. The DC—DC converter
1
has a control unit
20
constructed on a single-chip semiconductor substrate and a plurality of external devices.
The output signal, SG
1
, of the control unit
20
is supplied to the gate of a switching transistor
3
which is preferably comprised of a P channel MOS transistor. An input voltage Vin (the output voltage of an AC adapter
4
) is applied via a resistor R
1
to the source of the switching transistor
3
from the AC adapter
4
connected to an electronic apparatus.
The input voltage Vin is applied to a first output terminal EX
1
via the resistor R
1
and a diode D
1
. An output voltage Vout
1
is supplied to the internal circuits of the electronic apparatus from the first output terminal EX
1
.
The drain of the switching transistor
3
is connected to a second output terminal EX
2
via an output coil
5
and a resistor R
2
. The second output terminal EX
2
is connected to a battery BT and connected to the first output terminal EX
1
via a diode D
2
. A charge voltage Vout
2
of the battery BT is output from the second output terminal EX
2
.
The drain of the switching transistor
3
is also connected to the cathode of a flywheel diode
6
whose anode is connected to a ground GND. The node between the output coil
5
and the resistor R
2
is connected to the ground GND via a capacitor
7
. The output coil
5
and capacitor
7
constitute a smoothing circuit which smoothes the output voltage Vout
2
.
The control unit
20
includes first and second current detectors
8
and
9
, first to third differential voltage amplification circuits
10
,
11
and
12
, a PWM comparison circuit
13
, an oscillation circuit
14
and an output circuit
15
.
The first current detector
8
has two input terminals to which the voltage between the terminals of the resistor R
1
is supplied. The output terminal of the first current detector
8
is connected to the inverting input terminal of the first differential voltage amplification circuit
10
. The current detector
8
amplifies the voltage between the terminals of the resistor R
1
, thereby generating an output signal SG
2
, and sends the output signal SG
2
to the first differential voltage amplification circuit
10
.
The first differential voltage amplification circuit
10
amplifies a differential voltage between the voltage of the output signal SG
2
and a reference voltage (first threshold value) Vref
1
supplied to the non-inverting input terminal of the differential voltage amplification circuit
10
, generating an output signal SG
3
. The differential voltage amplification circuit
10
sends the output signal SG
3
to the PWM comparison circuit
13
.
The second current detector
9
has two input terminals to which the voltage between the terminals of the resistor R
2
is supplied. The output terminal of the second current detector
9
is connected to the inverting input terminal of the second differential voltage amplification circuit
11
. The current detector
9
amplifies the voltage between the terminals of the resistor R
2
, thereby generating an output signal SG
4
. The current detector
9
sends the output signal SG
4
to the second differential voltage amplification circuit
11
.
The second differential voltage amplification circuit
11
amplifies a differential voltage between the voltage of the output signal SG
4
from the second current detector
9
and a reference voltage (second threshold value) Vref
2
supplied to the non-inverting input terminal of the differential voltage amplification circuit
10
, generating an output signal SG
5
. The differential voltage amplification circuit
11
sends the output signal SG
5
to the PWM comparison circuit
13
.
The charge voltage Vout
2
is supplied to the inverting input terminal of the third differential voltage amplification circuit
12
. The differential voltage amplification circuit
12
amplifies a differential voltage between the voltage of the charge voltage Vout
2
and a reference voltage (third threshold value) Vref
3
supplied to the non-inverting input terminal of the differential voltage amplification circuit
12
, generating an output signal SG
6
. The differential voltage amplification circuit
12
sends the output signal SG
6
to the PWM comparison circuit
13
.
The output signals SG
3
, SG
5
and SG
6
of the first to third differential voltage amplification circuits
10
,
11
and
12
are supplied to the non-inverting input terminal of the PWM comparison circuit
13
. The oscillation circuit
14
supplies the inverting input terminal of the PWM comparison circuit
13
with a triangular signal SG
7
having a predetermined frequency.
The PWM comparison circuit
13
compares the triangular signal SG
7
with one of the output signals SG
3
, SG
5
and SG
6
of the first to third differential voltage amplification circuits
10
,
11
and
12
that has the lowest voltage. The PWM comparison circuit
13
outputs an L-level output signal SG
8
in a period where the voltage of the triangular signal SG
7
is higher than the output signal SG
3
, SG
5
or SG
6
, and outputs an H-level output signal SG
8
in a period where the voltage of the triangular signal SG
7
is lower than the output signal SG
3
, SG
5
or SG
6
.
The output signal SG
8
of the PWM comparison circuit
13
is supplied to the output circuit
15
. The output circuit
15
supplies the gate of the switching transistor
3
with the output signal SG
1
, as a duty control signal, which inverts the output signal SG
8
of the PWM comparison circuit
13
. Therefore, the switching transistor
3
is turned off when the duty control signal SG
1
has an H level and is turned on when the signal SG
1
has an L level.
In the DC—DC converter
1
, as the input voltage Vin is supplied from the AC adapter
4
, the output voltage Vout
1
and a circuit current I
1
are supplied to the internal circuits from the first output terminal EX
1
. The switching transistor
3
repeats the alternate ON action and OFF action in accordance with the duty control signal SG
1
output from the control unit
20
. As a result, a charge current IB is supplied to the battery BT from the second output terminal EX
2
.
In such an operation mode, as the input current Iin (I
1
+IB) from the AC adapter
4
increases, the voltage between the terminals of the resistor R
1
increases so that the voltage of the output signal SG
2
of the first current detector
8
rises. As a result, the voltage of the output signal SG
3
of the first differential voltage amplification circuit
10
drops. When the voltage of the output signal SG
3
becomes lower than the voltages of the output signals SG
5
and SG
6
, the L-level duration of the output signal SG
8
of the PWM comparison circuit
13
becomes longer. Consequently, the L-level duration of the duty control signal SG
1
becomes shorter, thus making the ON time of the switching transistor
3
shorter. This reduces the charge current IB of the battery BT.
As the input current Iin decreases, on the other hand, the volta

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