Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
1999-12-14
2001-05-08
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S037000
Reexamination Certificate
active
06229724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a power supply for a display monitor; and more particularly relates to a high efficiency Switching Mode Power Supply (SMPS) apparatus with a Power Factor Correction circuit (PFC).
2. Description of Related Art
Traditionally, a PFC circuit is used in devices with high wattage, which improves the power of an alternating-current transmission system so the voltage and the current are substantially in phase. But an increasing number of personal computers (PCs) having display monitors provide a remarkable potential for saving power by equipping the display monitors with a PFC circuit. Display monitors may also include other display devices which can be connected to a mains voltage and based for instances on cathode ray tube, liquid crystal or projection type display technology.
It is known in the art to use a separate PFC circuit between a mains outlet and a power consuming device. For example, EP 0 673 106 A1 discloses circuits for achieving a higher power factor in a switched mode power supply.
FIG. 2
of EP 0 673 106 A1 shows a circuit having a step-up regulator arranged between a bridge-type rectifier and an AC energy distribution source that includes a capacitor C, a transformer M, a controller CTRL
1
, a switch S
1
, a diode D
2
and a capacitor C
2
. One disadvantage in the related art is that the PFC circuit is always ON when main voltage is available. The reader is also referred to a technical disclosure by Siemens identified as the TDA 4862 datasheet.
It is also known in the art to add a PFC module, as such, inside a housing of such a power consuming device.
There is a need in the art to develop a cooperation between a display monitor and a PFC circuit in order to improve the efficiency of a power supply and power saving.
Moreover, many display monitors have a universal power supply, i.e., the same power supply is able to operate with a large value of the mains voltages for instance in US (110V) and in Europe (230V). Display monitors also have power saving properties. Display monitors are automatically switched to a power save state after inactivity of the user.
There is a need in the art to: (1) equip such display monitors power supplies with a PFC circuit which are also universal, i.e., properties of a PFC circuit are controlled according to the operating situation; (2) make a PFC circuit controllable according to mains voltage of display monitor; (3) make a PFC circuit controllable according to power consuming of a display monitor; and (4) find an economical solution where additional control circuitry for the PFC circuit is minimized by sharing an existent display controller for controlling power factor correction.
Moreover, PFC circuits known in the art provide a load with a fixed and regulated voltage that equals the mains voltage type. Regulated PFC output voltage is typically 400V in Europe (mains 230V) and 230V in US (mains 110V). In the art, universal monitors which cover both mains voltage types are working typically with a mains voltage range of 90V,. . . , 265V. The problem with fixed regulated PFC output voltages is the voltage gap between input voltage (the mains voltage) and output voltage. High voltage gap with high peak currents in inductor and switch increases losses in those components. Minimizing the voltage gap decreases losses in the inductor, switch and rectifier. This would allow a smaller and lighter inductor and switch, which would result in cost reductions.
FIG.
1
A Basic Display Monitor Power Supply Circuit
In particular,
FIG. 1
shows a basic display monitor power supply circuit generally indicated as
5
, which includes a mains rectifier
10
, a power factor correction circuit
30
, a main power supply
40
, a standby power supply
50
, deflection circuits
60
,
70
, a microcontroller
90
, a display user interface
100
and circuits
110
in addition to microcontroller
90
which are switched on during the power save mode.
The mains rectifier
10
provides a mains rectifier signal having a current and voltage having a certain phase relationship.
The power factor correction circuit
30
includes a PFC controller
31
, an inductor
32
, a diode
33
, a capacitor
34
, a control line
35
and a switch
36
. The PFC circuit
30
and also the PFC controller
31
are known in prior art. See the supply voltage generation in Siemens'
FIG. 3
of the TDA 4862 datasheet, which is a known prior art method. The PFC controller
31
monitors both the incoming full-wave rectified mains voltage and the voltage in the capacitor
33
a
. The product of these voltages is used to control the pulse ratio of the switch
36
so that the waveform of the current drawn from the mains corresponds to the waveform of the voltage. In
FIG. 3
of Siemens+ TDA 4862 datasheet, there is no external circuit controlled power supply generation. In
FIG. 1
, the combination of a transformer
37
, a diode
38
and a capacitor
39
provides for the voltage generation to the PFC circuit
30
. In operation, the alternating flux of the coil
32
induces alternating voltage in the transformer
37
, which is rectified by the diode
36
and filtered by capacitor
39
. One disadvantage of the display monitor power supply circuit
5
is that, when the standby state is activated by setting a switch to a continuous open state, the PFC controller
31
is still consuming power.
The main power supply
40
includes a switching mode power supply (SMPS) controller
41
, a transformer (T
1
)
42
, a switch
43
, a feedback loop
44
, an isolator (I
1
)
45
, diodes
46
a
,
46
b
,
46
c
, a feedback resistor
47
and a reference voltage diode
48
. The feedback loop is connected to a standby state control line
44
a
from the microcontroller
90
. All of these circuit components are all known in the art, the scope of the invention is not intended to be limited to any particular type thereof, and a person skilled in the art would appreciate how they cooperate to provide a main power supply. The function of the main power supply
40
will be explained in more detail below and further in relation to the description of
FIGS. 2-4
below.
The standby power supply
50
includes a switching mode power supply (SMPS) controller
51
, a transformer (T
1
)
52
, a switch
53
, a standby state feedback loop
54
, an isolator (I
1
)
55
, a diode
56
, a feedback resistor
57
and a reference voltage diode
58
. All of these circuit components are all known in the art, the scope of the invention is not intended to be limited to any particular type thereof, and a person skilled in the art would appreciate how they cooperate to provide a standby power supply. The function of the standby power supply
50
will be explained in more detail below and further in relation to the description of
FIGS. 2-4
below.
In operation, the SMPS controllers
41
,
51
control energy supplied to primary windings of the transformers
42
,
52
by switches
43
,
53
, which are preferably Field Effect Transistors (FETs). The SMPS controllers
41
,
51
can control, for instance, switching frequency and/or duty cycle. Feedback along lines
44
,
54
from the secondary side of transformers
42
,
52
is fed to the SMPS controllers
41
,
51
in order to keep rectified secondary voltages V
3
, . . . , V
6
stable. The display monitor circuits
60
, . . . ,
110
are all fed by the power supply. The switch SW
1
is a manual switch to start the power supply. The switch SW
3
is used to start the main power supply
40
by means of the standby power supply
50
. The switch SW
3
is controlled by isolator
45
and control line
44
from the microcontroller
90
. During standby, the switch SW
4
is closed and circuits
110
are supplied by standby power supply
50
. During normal operation, the switch SW
4
is open and circuits
110
are supplied by main power supply
40
.
Regarding the isolated
on-isolated interface, all parts in a given high wattage device which have galvanic connection to parts which the user can touch must be isolated from t
Nokia Corporation
Sterrett Jeffrey
Ware Fressola Van der Sluys & Adolphson LLP
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