Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2003-03-28
2004-12-14
Lee, Wilson (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S2090SC, C315S291000, C363S055000, C363S056010
Reexamination Certificate
active
06831423
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application is directed to inverter circuits used in the powering of discharge lamps, and more particularly to a third order high Q impedance matching inverter circuit with automatic line regulation electronic ballast for use with high power discharge lamps operating on a low input voltage.
Turning to
FIG. 1
, shown is a known, rapid start, second-order inverter circuit topology used for powering high power, low impedance discharge lamps. Such a circuit will have a 1 to 1.5 second delay between application of a starting signal and lamp ignition. Circuit
10
includes a full bridge input section
12
which receives an input from AC source
14
. The output of the full bridge section
12
is provided to a half bridge switching circuit network
16
, comprised of a first transistor switch
18
, a second transistor switch
20
, and a controller
21
. Output voltage from the half bridge switching circuit
16
is delivered to a resonant LC network
22
, including a resonant inductor
24
and a resonant capacitor
26
. The output from LC circuit
22
is provided to a lamp
28
, which is further connected to capacitive voltage divider network
30
, composed of capacitor
32
and capacitor
34
. A starting voltage of approximately 600 volts may be used as the ignition voltage. In this type of circuit, since the striking voltage is commonly only 600 volts, a preheat circuit (not shown) may be included to preheat the lamp prior to supplying the ignition voltage.
A drawback of the circuit depicted in
FIG. 1
is that it is not designed to operate efficiently with high impedance lamps. This is due, in part, to the use of lower input voltage. For example, when the input is a standard 120 volts, the circuit bus voltage may be about 150-160 volts. The AC voltage is approximately halved, due to the operation of switching network
18
, causing the AC output at the half-bridge switching network
18
to be approximately 75 volts. This voltage is sufficient to efficiently operate a low impedance lamp. However, if the lamp is a high impedance lamp, circuit
10
will need to draw an increased current, causing inefficient operation and stress on the components within the circuit.
Another drawback of the circuit in
FIG. 1
, is that in order to obtain an acceptable Q rating, if attempting to drive a high impedance lamp, a significantly higher voltage needs to be supplied to the lamp. In this situation, to obtain the desired Q rating, a larger sized resonant capacitor
26
and resonant inductor
24
is needed.
Further, the rapid start circuit
10
of
FIG. 1
, will maintain the preheat circuit active even after ignition of the lamp, resulting in a loss of about 1 to 1.5 watts of power.
If circuit
10
is attempted to be operated as an instant start lighting system, then the lamp starting voltage will be approximately 1300 volts. This higher voltage will need a higher resonant current, approximately 5 amps. The higher the current, the greater the stress on the inductor
24
, requiring a larger sized component. Increasing the size of the magnetics (i.e., inductor
24
) increases the cost of the magnetics, and increases the size of the housing in which the magnetics are held. The same switching current will also be seen by the half-bridge switching network
16
, which includes transistors
18
and
20
. To handle these higher currents, larger sized dies will be necessary, and therefore larger packages for transistors
18
and
20
will be used (the transistors may be FET, CMOS, bipolar or other appropriate transistor type). These larger, more robust transistors and capacitors carry an increased economic cost, require a larger physically sized lamp lighting system, as well resulting in decreased circuit efficiency.
Thus, if the second order inverter circuit
10
of
FIG. 2
is attempted to be used to drive high impedance lamps, a large starting current would be needed. It is known that when the starting current is higher, larger magnetics (i.e., inductor
24
), and transistors will be needed to handle the higher current, resulting in a less efficient lamp lighting system.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present application, an inverter circuit includes an input section configured to receive voltage from a voltage source and to input the voltage to the circuit. A switching network is connected to receive the input voltage from the input section. A controller is placed in operational connection with the switching network and is designed to control operation of the switching network. A resonant switching circuit is configured to receive an output from the switching network. Load connections are connected to the resonant switching circuit. A variable capacitance network is connected to the load connection to provide a variable capacitance during circuit operation.
In accordance with another aspect of the present application, a method is provided for operating an inverter circuit, including supplying a voltage from a voltage source to an input section. The received voltage is passed from the input section to a switching network. Operation of the switching network is being controlled by a controller, wherein a prescribed voltage is transmitted to a resonant circuit and a lamp voltage is delivered to a lamp connected to the resonant circuit. A voltage in a capacitor is clamped at predetermined levels. The clamping action acts to remove a fixed capacitor from the circuit or at least a portion of a cycle of operation of the circuit, wherein an effective variable circuit capacitance is obtained by operation of the clamping action.
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patent: 4533070 (1985-11-01), Sairanen et al.
patent: 4603378 (1986-07-01), Virta
patent: 5408403 (1995-04-01), Nerone et al.
patent: 5546300 (1996-08-01), Lee et al.
patent: 5729175 (1998-03-01), Ferrer
patent: 5796214 (1998-08-01), Nerone
patent: 5874810 (1999-02-01), Nerone
patent: 5877595 (1999-03-01), Nerone
patent: 6218788 (2001-04-01), Chen et al.
patent: 6469919 (2002-10-01), Bennett
patent: 6472827 (2002-10-01), Nilssen
Lin Y.L., et al.,Class L-a new single-ended DC-to-AC power inverter, Applied Power Electronics Conference and Exposition, 1997. APEC '97 Conference Proceedings 1997, Twelfth Annual Atlanta, GA, ISA Feb. 23-27, 1997, pp. 776-782, XP010215750 ISBN: 0-7803-3704-2.
Dinh Trinh Vo
Fay Sharpe Fagan Minnich & McKee LLP
General Electric Company
Lee Wilson
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