Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-02-09
2001-05-15
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C315S194000, C315S219000
Reexamination Certificate
active
06233162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. General Purpose of the Invention
The present invention relates to a power supply circuit; and more particularly to a power supply circuit for a monitor having a switching mode power supply (SMPS) circuit 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 lower wattage devices, like personal computers (PCs) having display monitors, provide a remarkable potential for saving power by equipping them with a PFC circuit. Display monitors may also include other display devices which can be connected to a mains voltage and based, for instance, 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
. 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 inside a housing of such a power consuming device.
Moreover, many devices 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 U.S. (110V) and in Europe (230V).
There is a need in the art to: (1) find an economical solution where additional control circuitry for the PFC circuit is minimized by sharing an existent power supply controller for controlling power factor correction; (2) make a PFC circuit controllable according to the mains voltage of the display monitor; and (3) equip display monitor power supplies with a PFC circuit which are also universal, i.e., properties of a PFC circuit are controlled according to the operating situation. The PFC inductor is large, heavy and expensive and there is a need to do PFC without adding an extra inductor.
In the art, universal monitors which cover both mains voltage types are working typically with a mains voltage range of 90V, . . . , 265V.
FIG. 1
(Prior Art): Basic Power Supply Circuit for a Display Monitor
In particular,
FIG. 1
, including
FIGS. 1A and 1B
, shows a basic power supply circuit generally indicated as
100
for a display user interface such as a display monitor
95
, which includes a mains filter
1
, a mains rectifier
10
, a power factor correction circuit
30
, a main power supply
40
, deflection circuits
60
,
70
, a video amplifier
80
and a microcontroller
90
.
In
FIG. 1A
, 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
34
. 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. 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 winding
37
, which is rectified by the diode
38
. One disadvantage of the display monitor power supply circuit
100
is that it needs extra components included in the PFC circuit
30
.
In
FIG. 1B
, the main power supply
40
includes a switching mode power supply (SMPS) controller
41
, a transformer
42
, a switch
43
, a feedback loop
44
, an isolator
45
, diodes
46
a
,
46
b
,
46
c
, a feedback resistor
47
and a reference voltage diode
48
. The feedback loop
44
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. 2-6
below.
In operation, the SMPS controller
41
controls energy supplied to primary winding
42
a
of the transformer
42
, by switch
43
, which is preferably a Field Effect Transistor (FET). The SMPS controller
41
, can control, for instance, switching frequency and/or duty cycle. Feedback along line
44
, from the secondary side of the transformer
42
, is fed to the SMPS controller
41
, in order to keep rectified secondary voltages V
1
, V
2
, V
3
stable. The display monitor circuits
60
, . . . ,
95
are all fed by the power supply.
Regarding the isolated
on-isolated interface, all parts in a given high wattage device which have calvanic connection to parts which the user can touch must be isolated from the mains voltage. Such isolation is realized with the transformer
42
, having adequate isolation between primary and secondary windings. The feedback signal
44
is fed from the secondary to primary winding via isolator
45
, which may be an opto-isolator.
There are disadvantages to the basic display monitor power supply circuit
100
shown in
FIG. 1
, which result primarily from the separate PFC circuitry
30
. The inductor
32
is large, heavy and expensive. The switch
36
must be a powerful switch, and the controller circuit
31
is also needed.
The present invention provides a solution to the aforementioned problems in the industry and also fulfills the aforementioned needs in the industry.
SUMMARY OF INVENTION
In particular, the present invention provides a power supply circuit for powering a user interface device such as a display monitor, which includes a switching mode power supply (SMPS) circuit and a voltage phase information (VPI) combiner circuit.
In operation, the SMPS circuit responds to a mains voltage signal (i.e. mains input) and also to a voltage phase information combiner signal (VFB) from the voltage phase information combiner circuit, for providing three different signals. The voltage phase information combiner signal (VFB) contains information about a phase relationship between a current drawn by the SMPS circuit and a voltage of the mains voltage signal.
The first two signals are provided back to the voltage phase information combiner circuit, and include a voltage phase information signal (VPI) containing information about a voltage phase of the mains voltage signal, as well as a voltage feedback signal containing information about the voltage of the switching mode power supply signal for powering the monitor. The third signal is the switching mode power supply signal for powering the monitor.
The voltage phase information combiner circuit responds to the voltage phase information signal (VPI) and the voltage feedback signal, for providing the voltage phase information combiner signal (VFB) to a controller of the SMPS circuit for shaping the current drawn by the SMPS circuit to substantially follow the phase of the mains voltage signal.
The voltage phase information combiner circuit may be in the form of a voltage modulated system or a frequency modulated system.
In the voltage modulated system, the voltage phase information combiner has a voltage phase information
Ikonen Raimo
Pistemaa Jari
Nokia Corporation
Riley Shawn
Ware Fressola Van Der Sluys & Adolphson LLP
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