Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-03-19
2003-05-13
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021120
Reexamination Certificate
active
06563720
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switching power supply device which is preferably used as a so-called A.C.-D.C. convertor, D.C.—D.C. convertor and so forth.
BACKGROUND OF THE INVENTION
There are switching power supply devices widely used for various apparatuses such as mobile electronic apparatuses. The devices switch a D.C., which is either obtained by rectifying/smoothing commercial A.C. or supplied from a battery, by applying high frequency around several hundred kHz so that the supplied voltage is effectively converted to a target value by means of a small transformer.
A typical example of this type of power supply device which has been widely used is a pulse-width modulation (PWM) type switching power supply device, which is a switching power supply device arranged such that in accordance with a result of detecting an output voltage on the secondary winding side by a voltage detection circuit, a control circuit controls a width of a switching pulse of a main switching element so that a target output voltage on the secondary winding side can be obtained.
Another example of the power supply device having been widely used is a ringing choke convertor (RCC) type switching power supply device, which is a power supply device arranged such that exciting energy accumulated in a transformer during a main switching element being turned on is transmitted to a circuit in the secondary winding side during the element being turned off, and after the transmission being finished the main switching element is turned on again by feeding a ringing pulse generated in a control winding of the transformer back to a control terminal of the element via a D.C. cut capacitor.
FIG. 8
is a block diagram showing an electrical arrangement of a typical conventional switching power supply device
1
. This switching power supply device
1
is an RCC-type switching power supply device in which a D.C., obtained by rectifying a commercial A.C.
3
by a main power supply circuit composed of a diode bridge
2
and a smoothing capacitor c
1
, is supplied to a circuit between a main power supply line
4
of a high-level side and a main power supply line
5
of a low-level side. The circuit between the main power supply lines
4
and
5
is arranged as a primary winding n
1
of a transformer n and a main switching element q are connected in series. The main switching element q is, for instance, a bipolar transistor or a field-effect transistor. Incidentally, in this example shown in
FIG. 8
, the field-effect transistor is adopted as the main switching element. The main switching element q is turned on or off by a control circuit
6
.
When the main switching element q is turned on, exciting energy is accumulated in the primary winding n
1
. Then the energy is induced to the side of a secondary winding n
2
during the element q is turned off, and after being smoothed in a diode d
1
and a smoothing capacitor c
2
, the energy is sent from output terminals
7
and
8
to an unillustrated load.
An output voltage between the output terminals
7
and
8
is divided by voltage dividing resistors r
1
and r
2
, and then the divided voltage is sent to one input of a comparator circuit
9
, while to the other input of the comparator circuit
9
, a reference voltage from a reference voltage source
10
is supplied. The value of the divided output voltage is compared with the reference voltage, and the result of the comparison is fed back to the control circuit
6
via a photodiode d
2
of a photocoupler pc
1
and a phototransistor tr
1
. The control circuit
6
transmits a drive signal to the main switching element q on the basis of: a D.C. voltage provided via a starting resistor r
3
; an induction voltage transmitted from an auxiliary winding n
3
of the transformer n; and output voltage information transmitted from the comparator circuit
9
via the photocoupler pc
1
, so that the circuit
6
controls the switching of the main switching element q to stabilize the output voltage of the switching power supply device
1
.
In the meantime, the switching power supply device
1
is provided with members for conducting the switching intermittently, namely a photocoupler pc
2
, a logic circuit
11
, comparators
12
and
13
, the above-mentioned reference source
10
, and voltage dividing resistors r
4
, r
5
, and r
6
, for lowering power consumption of the device
1
when an apparatus supplied power from the device
1
is in standby. In this arrangement, the control circuit
6
makes the main switching element q intermittently switch on or off at the time when a standby signal is supplied from a control input terminal
14
.
That is to say, the comparator
12
monitors the output voltage of the switching power supply device
1
so as to send a stop instruction to the control circuit
6
via the logic circuit
11
and the photocoupler pc
2
when a voltage value of the high-level side, divided by the voltage dividing resistors r
4
, r
5
, and r
6
, is not less than the reference voltage of the reference voltage source
10
, so that the comparator
12
stops the operation of the switching power supply device
1
. The comperator
13
also monitors the output voltage of the switching power supply device
1
so as to send a start instruction to the control circuit
6
via the logic circuit
11
and the photocoupler pc
2
when a voltage value of the low-level side, divided by the voltage dividing resistors r
4
, r
5
, and r
6
, is gradually decreased due to the stop of the switching operation so as to be not more than the reference voltage, so that the comparator
13
starts the operation of the switching power supply device
1
. The output voltage starts to increase again as the operation is resumed, and when the divided voltage value of the high-level side becomes not less than the reference voltage, the operation stops again, so that this sequence is repeated.
SUMMARY OF THE INVENTION
The conventional techniques have a problem such that a circuit arrangement is complicated. That is to say, apart from the comparator circuit
9
for monitoring the output voltage to stabilize the same, it is necessary to additionally provide the comparators
12
and
13
which are voltage monitoring means. Moreover, in accordance with the voltage information detected in the secondary winding side of the transformer n, the control circuit
6
in the primary winding side makes the switching power supply device operate intermittently. In this case the primary winding side cannot be directly connected to the secondary winding side since it interrupts the input being insulated from the output, so that these two have to be connected via the photocoupler pc
2
. Furthermore, the device has to receive the standby signal from the apparatus to which the power is supplied so that the device has to be connected to the apparatus using a control line as well as the power supply line, and moreover the apparatus has to be arranged as being capable of sending the control signal, when the device is adopted as an A.C. adapter.
The present invention aims at providing a switching power supply device with low power consumption when an apparatus to which the device supplies the power is in standby, with a simple arrangement.
To achieve the above-mentioned aim, the switching power supply device of the present invention, provided with control means for controlling switching of a main switching element that switches on or off a supplied D.C. voltage in accordance with output voltage information fed back from a secondary winding side so that an output voltage is stabilized to be a target voltage, includes:
fluctuation detection means, for detecting a fluctuation of controlling of the control means and transmitting a detected output in accordance with nonlinear output characteristics, only under a light load; and
superposition means, for attracting a fluctuation in the output from the fluctuation detection means and superposing the fluctuation on the output voltage information,
wherein the control means judges that the device operates under the light l
Conlin David G.
Edwards & Angell LLP
Jensen Steven M.
Nguyen Matthew
Sharp Kabushiki Kaisha
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