Ballast power control circuit

Details Ballast power control circuit Ballast power control circuit

1998-10-15

2001-01-30

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S2090SC, C315S240000, C315S24100S

Reexamination Certificate

active

06181082

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to circuits for driving a load and more particularly to ballast circuits for energizing one or more lamps.
BACKGROUND OF THE INVENTION
As is known in the art, a light source or lamp generally refers to an electrically powered element which produces light having a predetermined color such is a white or a near white. Light sources may be provided, for example, as incandescent light sources, fluorescent light sources and high-intensity discharge (HID) light sources such as mercury vapor, metal halide, high-pressure sodium and low-pressure sodium light sources.
As is also known, fluorescent and HID light sources can be driven by a ballast. A ballast is a device which by means of inductance, capacitance or resistance, singly or in combination, limits a current provided to a light source such as a fluorescent or a high intensity discharge light source, for example. The ballast provides an amount of current required for proper lamp operation. Also, in some applications, the ballast may provide a required starting voltage and current. In the case of so-called rapid start lamps, the ballast heats a cathode of the lamp prior to providing a strike voltage to the lamp.
As is also known, a relatively common ballast is a so-called magnetic or inductive ballast. A magnetic ballast refers to any ballast which includes a magnetic element such as a laminated, iron core or an inductor. Magnetic ballasts are typically reliable and relatively inexpensive and drive lamps coupled thereto with a signal having a relatively low frequency.
FIG. 1
shows an exemplary prior art magnetic ballast
10
for energizing a lamp
12
. The ballast
10
includes an inductive element or choke L and a capacitive element C which is coupled across first and second input terminals
14
a,b
of the ballast. The capacitive element C provides power factor correction for an AC input signal. In an exemplary embodiment, the choke has an impedance of about 1.5 Henrys and the capacitor C has a capacitance of about 3 microFarads.
The input terminals
14
a,b
are adapted for receiving the AC input signal, such as a 230 volt, 50 Hertz signal. The first input terminal
14
a
can be coupled to a so-called Phase (P) signal and the second input terminal
14
b
can be coupled to a so-called Neutral (N) signal. The lamp
12
includes first and second lamp filaments FL
1
,FL
2
with a starter circuit
16
coupled in parallel with the lamp filaments. Upon initial application of the AC input signal, the starter circuit
16
(, provides a short circuit so that current flows through the starter circuit thereby heating the lamp filaments FL
1
,FL
2
. After a time, the starter circuit
16
provides an open circuit as current flow through the lamp
12
is initiated. A voltage level of about 230 Volts is sufficient to strike the lamp
12
and cause current to flow between the filaments FL
1
,F
12
.
While such a circuit configuration may provide an adequate power factor, it is relatively inefficient and generates significant heat that must be dissipated. In addition, the circuit requires a starter circuit to initiate current flow through the lamp. Furthermore, the circuit is not readily adapted for providing a lamp dimming feature.
It would, therefore, be desirable to provide a ballast circuit that is efficient and allows the light intensity to be readily modified, i.e., dimming.
SUMMARY OF THE INVENTION
The present invention provides an efficient ballast circuit that includes a dimming feature for altering the intensity of light emitted by a lamp energized by the ballast. Although the invention is primarily shown and described as a ballast circuit, it will be appreciated that the invention has other applications as well, such as voltage regulation and electrical motors.
In one embodiment, a ballast circuit includes first and second input terminals for receiving an AC input signal which ultimately energizes a lamp. An inductive element or choke is coupled to the first input terminal and a capacitor is coupled between the inductive element and the second input terminal such that the capacitor and the lamp are connected in parallel. The inductive element and the capacitor are effective to generate a series resonance which can increase voltage at the lamp to a level above that of the input signal voltage. This arrangement allows a reduction in the size of the capacitor and increases efficiency as compared with conventional ballast circuits without sacrificing power factor correction advantages.
In another embodiment of a ballast circuit in accordance with the present invention, the circuit includes an inductive element and a plurality of capacitive elements coupled in parallel with the lamp. Each of the capacitive elements is coupled in series to a respective switch and each switch is controlled by a control circuit. A user interface is coupled to the control circuit for controlling the position of the switches. By controlling the switches based upon information from the user interface, a total capacitance provided by the parallel capacitors can be selected to achieve a desired intensity level for light emitted by the lamp.
In a further embodiment, a ballast circuit includes an inductive element and a plurality of capacitors coupled end to end in parallel with the lamp. Alternatively, the capacitors can be coupled in parallel with each other. At least one of the capacitors is coupled to a switching element for selectively shorting the capacitor. By controlling the duty cycle of the switching element, a predetermined capacitance level can be selected for setting light emitted by the lamp to a desired intensity level.
In still another embodiment, a ballast circuit includes an inductive element and a capacitor which is coupled in series with a first transformer winding such that the series-coupled capacitor and first winding are connected in parallel with the lamp. A second transformer winding, which is inductively coupled to the first winding, is coupled to a control circuit. The control circuit provides a signal to the second winding that is effective to cancel a predetermined amount of the flux generated by the first winding. In the case where the flux is substantially canceled, the first winding appears to the circuit as a relatively small DC resistance. By controlling the inductive impedance provided by the first winding, series resonance between the inductive element, the capacitor and the first winding can be manipulated to achieve a predetermined light intensity for the lamp.
In yet a still further embodiment, a ballast circuit has a series circuit path including a first input terminal, a first winding of a first transformer, a first inductive element, a first inductive detection element, a lamp, a second inductive detection element, and a second input terminal. A capacitor has one end coupled between the first inductive element and the first detection element and the other end coupled to the second input terminal. A second winding of the first transformer is coupled to a signal generator for providing a signal to the first transformer. A third inductive detection element, which is inductively coupled to the first and second detection elements, is coupled to a signal detector. In one embodiment, a detection circuit includes the inductive detection elements and the signal detector.
The signal generator, under the control of a user, generates a data signal on the second transformer winding that induces a corresponding signal on the first winding. The data signal generates a series resonance for current flowing through the first inductive element and the capacitor which is detected by the detection circuit. The information provided by the detected data signal can be used to control the power to the lamp to achieve a light intensity level selected by the user via the signal generator.


REFERENCES:
patent: 3808481 (1974-04-01), Rippel
patent: 4115729 (1978-09-01), Young et al.
patent: 4164785 (1979-08-01), Young et al.
patent: 4270164 (1981-05-01), Wyman et al.
patent: 4415839 (1983-11-01), Lesea

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