Battery operated power circuit and driving method thereof

Details Battery operated power circuit and driving method thereof Battery operated power circuit and driving method thereof

2001-04-17

2002-10-29

Vu, Bao Q. (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

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

C323S284000, C323S274000

Reexamination Certificate

active

06472854

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a step-down power supply; and, more particularly, to a step-down power circuit capable of extending operating time of a battery-operated power supply, a method for driving same, and further an electronic module implementing same.
BACKGROUND OF THE INVENTION
Conventionally, the voltage of a battery is lowered to a regulated level by a step-down switching made power supply in order to drive electronic circuitry of a portable electronic equipment, e.g., a notebook personal computer or a mobile phone.
Referring to
FIG. 1
, there is illustrated a conventional step-down switching power supply including an inductor
12
(an inductor for performing a smoothing operation, referred to as an inductor hereinafter), a first switching device
13
, a smoothing capacitor
14
, a rectifying diode
15
, a second switching device
16
, a smoothing capacitor
17
and a control IC (integrated circuit), i.e., a controller
18
.
The first switching device
13
is, e.g., an P-channel field effect transistor (FET) and serves to convert an input voltage (V
in
) provided from a battery (not shown) through an input terminal ll
a
to an output voltage (V
out
) provided to an output terminal
11
b
via the inductor
12
.
The smoothing capacitor
14
is connected between the output terminal
11
b
and the ground. The rectifying diode
15
is connected in parallel with the series connection of the inductor
12
and the smoothing capacitor
14
to sustain an electric current of the inductor
12
. The second switching device
16
is also an, e.g., N-channel FET and is coupled to the rectifying diode
15
in parallel. The smoothing capacitor
17
is coupled between the input terminal
11
a
and the ground.
The controller
18
detects the output voltage (V
out
) on the output terminal
11
b
and controls an on-off operation of the first and the second switching device
13
and
16
such that the output voltage (V
out
) can be maintained at a predetermined level. The switching devices
13
and
16
are controlled in such a manner that when the first switching device
13
is on, the second switching device
16
is controlled to be turned off, and vice versa.
According to the above described power circuit, when the switching device
13
is on, the input voltage (V
in
) from the input terminal lla is smoothed by the inductor
12
and the smoothing capacitor
14
and outputted to the output terminal
11
b
. Meanwhile, the controller
18
adjusts pulse widths of pulse signals, which control the on-off conversions of the first and the second switching device
13
and
16
, depending on a variation of the output voltage at the output terminal
11
b
to perform a feedback control. Accordingly, the regulated constant output voltage can be generated on the output terminal
11
b
.
As can be seen in
FIG. 2
, the controller
18
sets up a certain amount of dead time (t
DET
) between an on-state of the first switching device
13
and that of the second switching device
16
. Such dead time is required to prevent an undesirable cross current which can occur when both of the switching devices
13
and
16
are turned on concurrently.
Due to such complementary on-off operation of the first and the second switching device
13
and
16
, the energy accumulated in the inductor
12
can be emitted during a time period when the switching device
13
is off through the second switching device
16
, even when connected to the output terminal
11
b
is a heavy load (not shown) requiring a great amount of electric current. Accordingly, a highly efficient synchronous rectification can be achieved without suffering from a forward voltage loss which can be otherwise caused by the rectifying diode
15
.
In the step-down switching power circuit described above, the respective switching devices
13
and
16
are respectively set to be on and off simultaneously when the input voltage from the battery is reduced down close to the output voltage; and the switching device
13
is maintained at a conduction state without performing any further switching operations in order to maintain the output voltage at the regulated level and extend the operating time of the battery operated power circuit.
However, a considerable voltage drop occurs due to an electric resistance of the switching device
13
and the inductor
12
coupled in series between the input terminal
11
a
and the output terminal
11
b
. As a result, the output voltage V
out
cannot be maintained at the regulated value even though the switching device
13
is controlled to be on without interruption.
As shown in
FIG. 3
, the input voltage V
in
from the battery gradually decreases as the operation time of an electronic equipment increases. The output voltage V
out
declines slowly after the input voltage V
in
reaches a certain voltage value V
1
at a time t
1
. The voltage V
1
is the sum of a preset output voltage V
set
and a voltage-drop V
drp
, i.e., V
1
=V
set
+V
drp
, wherein the voltage-drop V
drp
is produced by a series resistance R
i1
of a turn-on resistance R
1
of the switching device
13
and a resistance R
L
of the inductor
12
.
Beyond t
1
, the output voltage V
out
continuously decreases to reach V
min
at a time t
1
′ the input voltage V
in
decreases. The portable electronic equipment ceases its operation when V
out
drops down to V
min
, the minimum operation voltage of the electronic equipment. As a result, the operation time of the electronic device can be extended by t
1
′−t
1
, which is limited by the considerably large constant voltage drop V
drp
.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a battery-operated step-down power circuit having longer operating time with wide range of operating condition, a method for driving such power circuit, and an electronic component or module capable of implementing the power circuit.
In accordance with a preferred embodiment of the present invention there is provided a power circuit capable of converting an input voltage into an output voltage through a switching and a smoothing operation, comprising: a switching device for performing the switching operation; an inductor for performing the smoothing operation, wherein the inductor is connected in series to the switching device; and a current control device connected in parallel to the switching device and/or the inductor.
In accordance with another preferred embodiment of the present invention, there is provided a power circuit, having a switching device and an inductor connected in series between an input terminal and an output terminal, for generating an output voltage on the output terminal by lowering an input voltage provided through the input terminal by a switching operation of the switching device and monitoring the output voltage to maintain the output voltage at a substantially constant level, the power circuit comprising: a current control device for adjusting an amount of an electric current provided from the input terminal to the output terminal in response to a control signal, wherein the current control device is connected between the input terminal and the output terminal in parallel to the switching device and an inductor; and a driving means for generating the control signal for controlling the current control device to maintain the output voltage at the constant level.
In accordance with still another preferred embodiment of the present invention, there is provided a driving method of a power circuit having a switching device and an inductor connected in series between an input terminal and an output terminal, wherein the power circuit generates an output voltage on the output terminal by lowering an input voltage provided through the input terminal by a switching operation of the switching device and monitors the output voltage to maintain the output voltage at a substantially constant level, the driving method comprising the steps of: providing a current control device for adjusting an amount of an electric current provi

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