Electric lamp and discharge devices: systems – Pulsating or a.c. supply – With power factor control device
Reexamination Certificate
2001-04-10
2002-10-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
With power factor control device
C315S2090SC, C315S291000
Reexamination Certificate
active
06459214
ABSTRACT:
BACKGROUND OF INVENTION
The present invention is directed to electronic ballasts, and more particularly to an inverter circuit topology which has improved operational efficiencies over existing electronic ballasts.
FIG. 1
illustrates a conventional parallel load, series resonant electronic ballast
10
. Electronic ballast
10
is supplied by an a.c. input source
12
. An input signal from input source
12
is rectified by full-bridge rectifier circuit
14
consisting of diodes
16
-
22
. The signal generated by full bridge rectifier circuit
14
is supplied, through an input filter
24
, to switching network
26
, consisting of switches
28
and
30
. Switches
28
and
30
are connected together at one end via node
37
, and may be controlled by a known controller
32
, such as a complementary switching system or other known design. Output from switching network
26
is supplied through inductor
34
to a lamp starting circuit
36
. Lamp starting circuit
36
includes d.c. blocking capacitor arrangement
38
with capacitors
40
and
42
, resonant capacitors
44
and
46
and a positive temperature co-efficient element
48
such as a thermister. D.C. blocking capacitors
40
,
42
are connected to each other at node
43
. Lamp
50
is connected to ballast
10
via cathodes
52
and
54
. Capacitor
55
is used as an energy storage capacitor. D.C. blocking capacitor arrangement
38
and capacitor
55
are connected at a first end to circuit bus
56
and at a second end to reference bus
57
. Upon initiation of operation a signal from switching network
26
causes energization of the lamp starting circuit
36
, wherein cathodes
52
and
54
are heated prior to the igniting of lamp
50
. Additional circuit connections are well known in the art, and are not shown for purposes of clarity for the present description.
Ballast
10
may be considered a parallel load, series resonant circuit in that lamp
50
is placed in parallel with resonant capacitors
44
and
46
which are in series with resonant inductor
34
. Positive temperature coefficient element
48
is provided parallel to resonant capacitor
44
to preheat the cathodes. Ballast
10
is useful for operation in single lamp that has low lamp arc current. It provides sufficient voltage for starting of lamp
50
, and also works efficiently during the running of lamp
50
following the breakdown of gases in the discharge lamp.
A drawback to the described conventional parallel load, series resonant ballast and other similar ballasts is that high current stresses which exist on the resonant components and switching devices for high bus voltage implementations. High bus voltage, for example, in Europe is approximately 325 volts, and in the U.S. it is in the range of 390 volts for 277 RMS voltage input.
High currents are problematic since the resulting high lamp arc current not only goes through the switching devices but also goes through, for example, the resonant inductor
34
. Therefore, resonant inductor
34
sees a summation of current which includes the lamp arc current and the resonant capacitor current through capacitors
44
and
46
. The lamp arc current may vary, depending upon what type lamps are used. For example, for a 28-watt compact fluorescent lamp (CFL) T-4, the lamp arc current may be 210 milli-amps, while for a T-6 2D lamp, the lamp current may be 360 milli-amps or higher. This means the resonant inductor needs to be of a significant size to avoid becoming saturated and to ensure that the power dissipation is not excessive. It is also necessary to use switches such as Field Effect Transistors (FETs), Bipolar Junction Transistors (BJTs) or other known switching devices having high current ratings.
Another drawback of ballast
10
is that it's resonant circuit has a poor power factor, where the input tank current and voltage are significantly out of phase, especially for the lamp with high lamp's arc current. An issue is that the signal delivered by switching network
26
from node
37
has its current and voltage out of phase, wherein the current through inductor
34
is out-of-phase with the voltage from node
37
to
43
. This out-of-phase state means more current to the tank than necessary to drive the lamp. For example, if only 30 watts were necessary in a fully in-phase system, in an out-of-phase system it may be necessary to deliver 50 or 60 watts of apparent power from the output of switches
28
and
30
. The excess apparent power circulates between resonant circuit
36
and switch network
26
resulting in the dissipation of a large amount of power in the components.
In these high voltage implementations it is necessary to use components sized to handle the noted stresses and excess current. However, these larger than desired components are more expensive than smaller components, and take up more physical space. Since the electronics industry is increasingly striving to decrease the cost and size of the ballasts, the foregoing noted inefficiencies are impediments to the objectives of the industry. This is especially true for ballasts used to power lamps such as integral compact fluorescent lamps, high intensity discharge lamps and others.
Therefore, it is considered desirable to configure an inverter circuit topology which improves the power factor of the ballast's tank circuit, to reduce the current stress on the resonant components and switching devices, allowing the use of smaller sized components. It is also desirable to provide a circuit which improves the output regulation over lamp impedance variations due to thermal effects, to provide a flexibility in preheating of the circuit, and for an overall improved and more economical ballast.
SUMMARY OF INVENTION
A high frequency, high power factor inverter circuit is provided to generate current for a load. A first inductor is connected to receive an input voltage. A second inductor is connected at one end to the load and at a second end to a first node. The second inductor is further magnetically coupled to the first inductor in a configuration which increases or boosts the voltage to the lamp. A first capacitive network is connected in parallel across the load. A second capacitive network is connected in series with the load, wherein the second capacitive network has a capacitive value larger than the first capacitive network. Prior to the load being activated, the first capacitive network and the load are operationally in parallel with each other, and the first capacitive network and first inductor are in series with each other. When the load is activated, the second capacitive network, the load, and the first inductor are operationally in series with each other. In a further embodiment, the first inductor and second inductor are not coupled together, rather the second inductor generates lagging current at a first node which acts to cancel leading current generated by the first capacitive network at the first node. The summation current at the first node may be less than the current otherwise seen by the system. Heating of the load, when it is a gas discharge lamp having cathodes is accomplished by the use of a cathode heater winding in operational connection with at least one of the cathodes and magnetically coupled to the first inductor.
REFERENCES:
patent: 5416387 (1995-05-01), Cuk et al.
patent: 5680015 (1997-10-01), Bernitz et al.
patent: 5936357 (1999-08-01), Crouse et al.
patent: 5969483 (1999-10-01), Li et al.
patent: 6137239 (2000-10-01), Wu et al.
patent: 6169374 (2001-01-01), Chang
patent: 6281636 (2001-08-01), Okutsu et al.
patent: 6337800 (2002-01-01), Chang
Chen Timothy
Cosby Melvin C.
Skully James K.
Fay Sharpe Fagan Minnich & McKee LLP
General Electric Company
Tran Chuc
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