Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
1999-12-22
2002-03-19
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S291000, C315S224000, C315SDIG007
Reexamination Certificate
active
06359394
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling the operation of a high intensity discharge lamp and, more specifically for controlling a high intensity discharge lamp during lamp ignition and steady state operation.
A conventional high intensity discharge (HID) ballast, shown in
FIG. 1
, receives a power from an AC mains
100
. A preconditioner/up-converter
110
includes circuitry for rectification of the AC power, power factor correction and for boosting of the AC peak voltage.
A regulated DC voltage (Vbus) is supplied to an inverter
120
(e.g. full-bridge type). The inverter output is supplied to the serial combination of a blocking capacitor Cs, inductor L and capacitor C. Inductor L and capacitor C form a resonant circuit. Inverter
120
typically operates at a switching frequency so as to be in an inductive mode (i.e. above the resonant frequency of the resonant circuit). Lamp
130
is connected across capacitor C.
A fixed voltage divider circuit
210
includes a plurality of resistors R
1
, R
2
, R
3
and R
4
and a pair of taps t
1
and t
1
′ between resistors R
1
and R
2
and between resistors R
3
and R
4
, respectively. A circuit
210
including a pair of voltage dividers divides down/sets the differential lamp voltage such that a sample
220
of the latter is at a conventional electronics level suitable for input to an integrated circuit
3
. Integrated circuit
3
serves as a controller for controlling operation of lamp
130
.
An ignitor (not shown) typically can produce ignition voltages of about 3.5 kilovolts (KV). In order to sample the lamp voltage during ignition, the lamp voltage is lowered or divided down to a usable level of less than 15 volts through circuit
210
. Unfortunately, voltage divider circuit
210
will lower or divide down steady-state voltages, typically of about 200 volts, to less than 1-volt full scale. Voltages of such small magnitude are too small to yield good resolution, that is, are too small in magnitude to accurately reflect lamp operating conditions.
It is therefore desirable to provide a new and improved ballast which includes a sampling scheme for accurately reflecting lamp operating conditions during ignition and steady-state conditions.
SUMMARY
In accordance with a first aspect of the invention, a ballast for powering a high intensity discharge lamp includes an inverter for supplying power to the lamp, at least one voltage divider for sampling a lamp operating condition and producing a sampled signal based on a scaling factor applied to the sampled lamp operating condition and a controller for driving the inverter in response to the sampled signal. The scaling factor varies based on the mode of lamp operation.
The sampled signal is always of a sufficient magnitude to yield good resolution. Consequently, lamp operating conditions can be accurately monitored. The magnitude of the sampled signal is maintained at an acceptable level by varying the scaling factor based on the mode of lamp operation.
It is a feature of this first aspect of the invention that the mode of lamp operation includes lamp ignition and steady-state lamp operation. Typically, the scaling factor applied is substantially larger during lamp ignition than during steady-state lamp operation. It is another feature of this first aspect that the at least one voltage divider includes two strings of resistors and further includes a pair of switches. Each switch selects which of the resistors from an associated string are to be coupled to the controller in response to instructions from the controller.
In accordance with a second aspect of the invention, a method of operating a high intensity discharge lamp ballast includes the steps of applying a scaling factor to a sampled lamp operating condition in producing a sampled signal, driving an inverter in response to the sampled signal, and varying the scaling factor based on the mode of lamp operation. The step of varying the scaling factor includes substantially reducing the scaling factor applied to the sampled lamp operating condition during steady-state lamp operation as compared to lamp ignition operation.
Accordingly, it is an object of the invention to provide an improved ballast which includes a sampling scheme for accurately reflecting lamp operating conditions during ignition and steady-state conditions.
Still other objects and advantages of the invention will, in part, be obvious and will, in part, be apparent from the specification.
The invention accordingly comprises several steps in the relation of one or more such steps with respect to each of the others, and a device embodying features of construction, combination of elements, and arrangements of parts which are adapted to effect such steps, all is exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
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patent: 5103141 (1992-04-01), Keijser et al.
patent: 5198728 (1993-03-01), Bernitz et al.
patent: 5262701 (1993-11-01), Derra et al.
patent: 5343122 (1994-08-01), Sugimori et al.
patent: 5557207 (1996-09-01), Duve
patent: 5600211 (1997-02-01), Luger
patent: 5742134 (1998-04-01), Wacyk et al.
patent: 6057651 (2000-05-01), Usami
patent: 6060843 (2000-05-01), Primisser et al.
patent: 0228123 (1987-07-01), None
patent: 0459126 (1991-12-01), None
patent: 0735801 (1996-10-01), None
Phillips Electronics North America Corporation
Vo Tuyet T.
Wong Don
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