Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-12-07
2001-02-13
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S056070, C363S131000, C323S902000
Reexamination Certificate
active
06188584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply circuit for use in an electronic apparatus such as a video projector or a television receiver.
2. Description of the Prior Art
Recently in an electronic apparatus such as a video projector, a television receiver and so forth for projecting image, there is employed a system which, even when a main power source thereof is placed in its off-state, enables a user to close the main power source again by turning on a main power switch of the apparatus by means of a remote controller or the like.
The power supply circuit of this type known heretofore has such a circuit configuration as that shown in FIG.
3
. The power supply circuit shown in
FIG. 3
has a power plug
1000
, a primary circuit
1001
and a secondary circuit
1002
. The power plug
1000
is capable of inserting into, e.g., an outlet of a commercial AC power source for supplying an AC input voltage. The power plug
1000
is connected to a relay switch
1003
, a rectifier diode bridge
1004
and so forth in the primary circuit
1001
of transformers
1020
and
1021
. The rectifier diode bridge
1004
is connected to a main switching power circuit
1005
. Power is supplied to a standby switching power circuit
1006
from a half-wave rectifier circuit consisting of a diode
1031
and a capacitor
1032
.
The secondary circuit
1002
of the transformers
1020
and
1021
is equipped with a relay controller
1007
and a microcomputer
1009
for turning on or off the relay switch
1003
. The relay switch
1003
is disposed in the primary circuit
1001
relative to the main switching power circuit
1005
and the standby switching power circuit
1006
. Meanwhile a relay control coil
1008
is disposed in the secondary circuit
1002
relative to the main switching power circuit
1005
and the standby switching power circuit
1006
.
In the known power supply circuit of
FIG. 3
mentioned above, it is necessary to dispose the secondary coil, the rectifier and the regulator of the standby switching power circuit
1006
on the side of the secondary circuit
1002
side, and also to dispose the relay control coil
1008
and the power switch
1010
on the same side for turning on the main switching power circuit
1005
, and further to dispose the relay switch
1003
and the main switching power circuit
1005
in the primary circuit
1001
. When the power switch
1010
is turned on in a state where an on-control signal from the microcomputer
1009
is applied to the base of a transistor
1030
, then the transistor
1030
is switched on to cause a current flow in the relay control coil
1008
, thereby turning on the relay switch
1003
. Consequently, the main switching power circuit
1005
is driven to deliver a desired main power output
1011
.
Since the relay switch
1003
and the relay control coil
1008
are housed normally in one casing, the secondary circuit
1002
including the relay control coil
1008
is so positioned as to be proximate to the primary circuit
1001
with partial entry.
However, in view of conforming with required safety standards, a certain electrical insulation distance needs to be insured between the primary circuit
1001
and the secondary circuit
1002
.
For this reason, it is necessary to space the primary circuit structure and the secondary circuit structure apart from each other by increasing the area of a substrate where the primary circuit
1001
including the relay switch
1003
and the secondary circuit
1002
including the relay controller
1007
are formed.
Similarly in view of conforming with the required safety standards, the level of any spurious radiation noise generated in the electronic apparatus and leaking via its power cord needs to be reduced under a predetermined value. In preventing harmful influence of such spurious radiation noise generated from the secondary circuit
1002
and induced to the primary circuit
1001
, there exists a problem of necessitating increase of the substrate area to reduce the leakage level of the spurious radiation noise from the secondary circuit
1002
to the primary circuit
1001
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a power supply circuit which is adapted for curtailing the area of a circuit substrate and reducing any spurious radiation from a secondary circuit to a primary circuit while insuring a proper electrical insulation distance between the secondary and primary circuits.
According to one aspect of the present invention, there is provided a power supply circuit for converting an AC voltage of an input AC power into a desired DC output voltage. This power supply circuit comprises a first rectifying smoother for generating a DC voltage from the AC power supplied thereto; a standby power source supplied with the DC voltage from the first rectifying smoother and having a plurality of DC outputs; a second rectifying smoother for converting the AC voltage into a DC voltage; a main power source for converting the DC voltage of the second rectifying smoother into the desired DC output voltage; a main switch for turning on the main power source; a relay controller disposed on the primary side of the main power source and the standby power source and, in response to turn-on of the main switch, actuated by the first of the plural DC outputs obtained from the standby power source; and a relay switch disposed on the primary side of the main power source and the standby power source and, upon actuation of the relay controller, driven to connect the second rectifying smoother to the AC power source.
Since the relay controller and the relay switch are both disposed on the primary side of the main power source and the standby power source, the relay controller and the relay switch are positionally in mutual proximity, but the primary side of the main and standby power sources is not proximate to the secondary side of the main and standby power sources without the necessity of any particular portion for electromagnetic insulation, whereby the substrate area can be curtailed. Moreover, this structure is effective to reduce the leakage level of any spurious radiation noise from the relay controller to the relay switch.
The above power supply circuit further comprises a control means disposed on the secondary side of the main power source and the standby power source, and fed with an input signal which indicates an on-state or an off-state of the main switch, wherein the standby power source supplies the second of the plural DC outputs as a voltage for actuating the control means.
In this instance, the standby power source can supply the voltage for actuating to the control means.
The power supply circuit mentioned above further comprises a first optical switch for transmitting the signal, which indicates the on/off state of the main switch, to the control means, wherein the first optical switch consists of a light emitting element and a light receiving element to receive the light from the light emitting element, and the first optical switch is an electromagnetically insulating element disposed between the primary side of the main and standby power sources and the secondary side of the main and standby power sources.
Thus, electromagnetic insulation can be achieved between the primary side and the secondary side of the main and standby power sources.
In the power supply circuit mentioned above, the relay controller has a relay control coil, wherein the relay controller receives a control signal from the control means, and when the main switch is turned on, the relay controller operates the relay control coil thereof to turn on the relay switch.
Also in the power supply circuit mentioned above, the relay controller has a second optical switch turned on by the control signal from the control means, wherein the second optical switch consists of a light emitting element and a light receiving element to receive the light from the light emitting element; and the second optical switch is an electromagnetically insulating elem
Arai Tsutomu
Shinobu Hiroshi
Frommer William S.
Frommer Lawrence & Haug LLP.
Kessler Gordon
Sony Corporation
Vu Bao Q.
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