Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
2000-09-08
2002-03-26
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S066000, C307S116000, C307S139000
Reexamination Certificate
active
06362541
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the design of power supply circuits for electrical and electronic equipment. More specifically, the present invention pertains to the reduction of power consumption in a display device in standby mode.
2. Related Art
With the increasingly widespread use of display devices in businesses, education and the typical household, such as those used in computer systems, much effort is constantly expended in an attempt to reduce the power consumption of display devices so as to conserve energy. Many display devices today provide a mechanism by which the appliance enters a “standby mode” after a period of inactivity. While in the standby mode, the device consumes less power than it does while in active use, commonly referred to in the art as being in its “main mode” under normal operating conditions. When activity resumes, the device exits its standby mode and reenters its main mode, wherein power consumption returns to the normal operating level. As such, power is conserved in standby mode wherein the device remains “on” even though it is not currently being used, and the requisite power level for main mode operation is promptly restored upon the resumption of active use.
Nevertheless, a recent European regulation has stipulated that power consumption of display devices in standby mode is to be less than one watt instead of three watts. This and other similar regulatory changes and the need to conserve power call for the industry to develop new circuits for implementing standby mode in display devices that can meet new power consumption requirements.
To implement power mode switching between main mode and standby mode in a display device as described above, several prior art circuits have been developed to use the synchronization (sync) signal(s), e.g., horizontal sync (h-sync) signal, vertical sync (v-sync) signal, sent from a computer to a display device (e.g., CRT monitor) and lack thereof as a trigger to switch between main mode and standby mode. In the display device art, it is known that with respect to the two sync signals, either separately or as a composite sync signal, when both the h-sync (horizontal) and v-sync (vertical) signals are present, the display device should be in main mode; that when only the v-sync signal is present, the display device should be in suspend mode; and that when only the h-sync signal is present, the display device should be in standby mode. Thus, a sync detect circuit can be used in conjunction with a microprocessor to monitor the sync signal(s) and control the voltage supplied to the monitor accordingly, thereby controlling the power it consumes.
Prior Art
FIG. 1
illustrates one prior art circuit
100
wherein two power supplies are used to implement switching between main mode and standby mode. More particularly, prior art circuit
100
has an alternating current (AC) power input
101
and two separate power supplies
110
and
120
, wherein AC input
101
is coupled to a main power supply
110
and a standby power supply
120
in parallel. Additionally, a microprocessor
130
is coupled between main power supply
110
and standby power supply
120
. Further, a sync detect circuit
140
is coupled between standby power supply
120
and microprocessor
130
. Sync detect circuit
140
is also coupled to a computer
199
. In this prior art circuit
100
, when the display device is operating in main mode, main power supply
110
provides power to the display CRT and other circuit elements (e.g., microprocessor
130
and sync detect circuit
140
) via outputs
111
,
112
,
113
and
114
. Typical values for these outputs of main power supply
110
are: +200 volts for output
111
, +80 volts for output
112
, +16 volts for output
113
, and −16 volts for output
114
. With these exemplary values, outputs
111
and
112
are typically coupled to the display CRT, and outputs
113
and
114
are typically coupled to the horizontal and vertical differentials (h-diff and v-diff) of the display device. In the same circuit
100
, when the display device is in standby mode and the display CRT is inactive, standby power supply
120
provides power to microprocessor
130
via output
123
(e.g., 5 volts or 3.3 volts) and to sync detect circuit
140
via output
124
(e.g., 5 volts or 3.3 volts).
Still referring to Prior Art
FIG. 1
, sync detect circuit
140
serves as a buffer between computer
199
and microprocessor
130
. When sync detect circuit
140
no longer detects a sync signal
194
from computer
199
, sync detect circuit
140
sends a “no_sync” signal
143
to microprocessor
130
, which in turn sends an “off” signal
131
to main power supply
110
. In response to off signal
131
, main power supply
110
is turned off and the display device enters standby mode. Note that standby power supply
120
remains on while the display device is in standby mode to power microprocessor
130
and sync detect circuit
140
. In other words, standby power supply
120
is always “on” irrespective of whether the display device is in main mode or standby mode. As such, sync detect circuit
140
continues to monitor for sync signal
194
from computer
199
while the display device is in standby mode. Upon detecting the resumption of signal
194
from computer
199
, sync detect circuit
140
sends a “sync” signal
143
to microprocessor
130
, which in turn sends an “on” signal
131
to main power supply
110
. In response, main power supply
110
is turned on again and the display device thus resumes its main mode of operation.
One major disadvantage of prior art circuit
100
of
FIG. 1
is that standby power supply
120
remains on even when the display device is in standby mode. The constant presence of an active power supply in circuit
100
means that power loss due to switching action of the power supply (switching loss) cannot be avoided. Consequently, it is difficult to achieve a low power consumption level using prior art circuit
100
. For example, with AC input
101
at approximately 230 volts, as it is typically the case for European appliances, and with the exemplary values described above with respect to outputs
123
and
124
(5 volts or 3.3 volts), prior art circuit
100
cannot consistently achieve a standby power consumption of 1 W or less, as is required by the new European standard. Furthermore, prior art circuit
100
is also expensive to implement because an extra power supply, namely, standby power supply
120
, is always required in addition to main power supply
110
. As such, a circuit for power mode switching in a display device which consistently achieves less than 1 W power dissipation in standby mode and which is inexpensive to build is needed.
FIG. 2
illustrates another prior art circuit
200
wherein a single power supply is used to implement switching between main mode and standby mode. More specifically, prior art circuit
200
has an AC power input
201
and a power supply
210
, wherein AC input
201
is coupled to power supply
210
having four outputs
211
,
212
,
213
and
214
. Typical values for these outputs of power supply
210
while the display device is in main mode are: +200 volts for output
211
, +80 volts for output
212
, +16 volts for output
213
, and −16 volts for output
214
. Moreover, outputs
211
and
212
are typically coupled to the display CRT, and outputs
213
and
214
are typically coupled to the horizontal and vertical differentials (h-diff and v-diff) of the display device. Also, output
211
is coupled to a voltage drop circuit
250
, and output
213
is coupled to a voltage regulator
260
. Voltage regulator
260
is coupled to a microprocessor
230
via line
263
, and to a sync detect circuit
240
via line
264
. Thus, voltage regulator
260
is coupled between power supply
210
and microprocessor
230
, as well as between power supply
210
and sync detect circuit
240
. Sync detect circuit
240
is further coupled to microprocessor
230
and to a compute
Ballato Josie
Polk Sharon
Sony Corporation of Japan
Wagner , Murabito & Hao LLP
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