Switching power supply unit

Details Switching power supply unit Switching power supply unit

2002-06-27

2003-12-30

Vu, Bao Q. (Department: 2838)

Electric power conversion systems

Current conversion

Having plural converters for single conversion

C363S065000, C363S070000

Reexamination Certificate

active

06671194

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power supply unit having stand-by output.
2. Description of the Prior Art
Conventionally, widely used is a switching power supply unit that is configured to switch a direct current obtained by rectifying and smoothing a commercial alternating current, for example, at high frequency of about 100 kHz and convert the current into a desired voltage by a transformer.
As a system for controlling an output voltage in the switching power supply unit, employed is the system such as a pulse width modulation (PWM) control system that controls a duty ratio of a switching pulse in accordance with changes in the output voltage, a frequency control system or phase control system adopting resonance that controls a frequency or phase of a switching pulse, etc.
In general, in regard to a switching power supply unit included in an electrical apparatus such as a television receiver, or home video system, etc., a main power supply circuit and a stand-by power supply circuit are provided together as shown in
FIG. 1
, for example, so as to supply a main power supply necessary for the apparatus in an operation state and a stand-by power supply necessary in a stand-by state.
More specifically, a conventional switching power supply unit
200
shown in
FIG. 1
comprises a main power supply circuit
240
for main output, which is connected to a commercial alternating current power supply AC through a relay switch SW
1
, and a stand-by power supply circuit
280
for stand-by output, which is independent of the main power supply circuit
240
.
The main power supply circuit
240
is configured to switch the rectified smoothed output provided by a main rectifying and smoothing circuit
210
, which rectifies and smooths an alternating current power supply input, by a main converting circuit
220
, and rectify and smooth the output of a main converting transformer
225
, to which the switched output provided by the main converting circuit
220
is supplied, in a main output circuit
230
, thereby obtaining a main output.
The stand-by power supply circuit
280
is configured to switch the rectified smoothed output provided by a sub rectifying and smoothing circuit
250
, which rectifies and smooths the alternating current power supply input, by a sub converting circuit
260
, and rectify and smooth the output of a sub converting transformer
265
, to which the switched output provided by the sub converting circuit
260
is supplied, in a stand-by output circuit
270
, thereby obtaining a stand-by output.
The main rectifying and smoothing circuit
210
in the main power supply circuit
240
is constituted by a rectifying circuit
211
, a power-factor improvement circuit (PFC)
212
, and a smoothing capacitor
213
. More specifically, the main power supply circuit
240
supplies a main power supply necessary for the apparatus including the circuit in an operation state, and thus has large output power. For this reason, the power-factor improvement circuit
212
is provided in the main rectifying and smoothing circuit
210
to reduce a high frequency current that exerts a harmful influence on power equipments etc.
On the other hand, the stand-by power supply circuit
280
supplies a stand-by power supply necessary for the apparatus including the circuit in a stand-by state to, for example, a remote control circuit. Therefore, the output power of the circuit is in such a degree that a power-factor improvement circuit is not required, and the sub rectifying and smoothing circuit
250
in the stand-by power supply circuit
280
is constituted by a rectifying circuit
251
and a smoothing capacitor
252
.
In the conventional switching power supply unit
200
constructed as described above, in the case that AC input is cut, the lower the AC input voltage is, the smaller the amount of charge stored in the smoothing capacitor
252
of the sub rectifying and smoothing circuit
250
in the stand-by power circuit
280
in which no power-factor improvement circuit is provided becomes in comparison with the amount of charge stored in the smoothing capacitor
213
of the main rectifying and smoothing circuit
210
in the main power supply circuit
240
that comprises the power-factor improvement circuit
212
. Therefore, the output from the stand-by power supply circuit
280
stops before the output from the main power supply circuit
240
stops.
Meanwhile, in regard to electronics including a switching power supply unit, in the case that the stand-by power supply is not desired to stop before the main power supply stops, for example, in the case that a system performs an ending process with a stand-by power supply at the time of cutting an AC input, the following measures are taken so that the stand-by power supply does not stop before the main power supply stops.
The capacity of the smoothing capacitor
252
provided in the sub rectifying and smoothing circuit
250
of the stand-by power supply circuit
280
is increased so that the holding time of output in the stand-by power supply circuit
280
becomes equal to or above one in the main power supply circuit
240
.
Alternatively, a power-factor improvement circuit is also provided in the sub rectifying and smoothing circuit
250
of the stand-by power supply circuit
280
so that the holding time of output in the stand-by power supply circuit
280
becomes equal to or above one in the main power supply circuit
240
.
However, in a normal operation state in that an alternating current supply is supplied, the smoothing capacitor
252
in the sub rectifying and smoothing circuit
250
exceeds the capacity limit, or the sub rectifying and smoothing circuit
250
of the stand-by power supply circuit
280
has an unnecessary power-factor improvement circuit.
Therefore, if such measures described above are taken, they cause harmful effects for miniaturizing, reducing cost, and improving reliability of the switching power supply unit.
SUMMARY OF THE INVENTION
To solve the problem described above, an object of the present invention, which has been achieved in view of the situation described above, is to provide a switching power supply unit, which does not have excesses of capacity and a power-factor improvement circuit, which is not fundamentally necessary, and is configured in that the stand-by power supply does not stop before the main power supply does at the time of cutting an AC input.
According to an aspect of the invention, a switching power supply unit is characterized by comprising: a main rectifying and smoothing circuit which rectifies and smooths alternating current power supply input; a main converting circuit connected to the main rectifying and smoothing circuit; a main converting transformer to which the switched output provided by the main converting circuit is supplied; a main output circuit which rectifies and smooths the output from the main converting transformer and obtains main output; a sub rectifying and smoothing circuit which rectifies and smooths the alternating current power supply input; a sub converting circuit connected to the sub rectifying and smoothing circuit; a sub converting transformer to which the switched output provided by the sub converting circuit is supplied; a stand-by output circuit which rectifies and smooths the output from the sub converting transformer and obtains stand-by output; and a back-up circuit which supplies direct current output obtained by the main rectifying and smoothing circuit.


REFERENCES:
patent: 5612581 (1997-03-01), Kageyama
patent: 5894414 (1999-04-01), Jiang
patent: 6014322 (2000-01-01), Higashi et al.
patent: 6118674 (2000-09-01), Higashi
patent: 6229723 (2001-05-01), Umetsu et al.
patent: 6414864 (2002-07-01), Hoshi
patent: 6525947 (2003-02-01), Umetsu et al.

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