Patent Application
20120161655
The present invention relates to lighting, and more specifically, to electronic ballasts for operating one or more lamps.
A typical ballast converts alternating current (AC) power from an AC power supply so that it is suitable for energizing one or more lamps connected to the ballast. A ballast may include a rectifier for generating a direct current (DC) signal from the AC power received from the AC power supply, a power factor correction circuit for correcting the DC signal generated by the rectifier, and an inverter for converting the corrected DC signal to an oscillating voltage for providing to the lamp.
A ballast is used to provide power for energizing various types of lamps, such as but not limited to gas discharge lamps. A gas discharge lamp, such as a fluorescent lamp, converts power received from the ballast into visible energy (i.e., light). While gas discharge lamps are commonly used in various lighting applications, they often produce a visual effect known in the art as “striations.” Striations refer to alternating bands of bright and dim areas that form along an axis of a tube of a gas discharge lamp. They may take the appearance of a standing wave.
Embodiments of the present invention provide a ballast designed to minimize striations from being produced by a lamp when the lamp is powered by the ballast. The ballast is configured for connecting to an alternating current (AC) power supply, and includes a rectifier for receiving an AC voltage signal via the power supply and producing a rectified voltage signal therefrom. A power factor correction circuit receives the rectified voltage signal and provides a corrected voltage signal. An inverter circuit receives the corrected voltage signal and generates an oscillating power signal for energizing the lamp as a function of the corrected voltage signal. The power signal has a waveform cycle comprising a first pulse that has a first integral value, and a second pulse that has a second integral value.
In an embodiment, there is provided a ballast to energize at least one lamp. The ballast includes: an inverter circuit to provide an oscillating power signal to energize the at least one lamp, wherein the oscillating power signal has a waveform cycle comprising a first pulse that has a first integral value and a second pulse that has a second integral value, wherein the inverter circuit includes: a first transistor having a first gain (hFE1), wherein the first transistor is configured to alternately operate between a conductive state and a non-conductive state; and a second transistor having a second gain (hFE2), wherein the second transistor is configured to alternately operate between a conductive state and a non-conductive state; wherein when the first transistor operates in the conductive state, the second transistor operates in the non-conductive state and the first pulse of a waveform cycle of the oscillating power signal is generated and the first integral value of the first pulse is a function of first gain (hFE1); wherein when the second transistor operates in the conductive state, the first transistor operates in the non-conductive state and the second pulse of a waveform cycle of the oscillating power signal is generated and the second integral value of the second pulse is a function of the second gain (hFE2); and wherein the first integral value of the first pulse of each waveform cycle of the oscillating power signal is different from the second integral value of the second pulse of each waveform cycle such that a differential relationship between first gain (hFE1) and the second gain (hFE2) is greater than or equal to a minimum value in order to minimize striations in the at least one lamp.
In a related embodiment, the differential relationship may include
In another related embodiment, the minimum value may be dependent on an expected ambient temperature for the ballast. In a further related embodiment, the minimum value may be equal to 1 when the expected ambient temperature for the ballast is around 21 degrees Celsius. In another further related embodiment, the minimum value may be equal to 2 when the expected ambient temperature for the ballast is around 8 degrees Celsius.
In yet another related embodiment, the ballast may further include: a rectifier to receive an alternating current (AC) voltage signal and to produce a rectified voltage signal therefrom; and a power factor correction circuit to receive the rectified voltage signal and to provide a corrected voltage signal, wherein the inverter circuit may be connected to the power factor correction circuit and the inverter circuit may be configured to generate the oscillating power signal as a function of the corrected voltage signal. In still another related embodiment, the ballast may be configured to energize a plurality of lamps.
In another embodiment, there is provided a ballast to energize at least one lamp. The ballast includes: an inverter circuit to provide an oscillating power signal to energize the at least one lamp, wherein the oscillating power signal has a waveform cycle comprising a first pulse that has a first integral value and a second pulse that has a second integral value, and wherein the inverter circuit includes: a first transistor having a first gain (hFE1) and configured to alternately operate between a conductive state and a non-conductive state, wherein the first transistor has a base terminal, a collector terminal, and an emitter terminal; a first drive circuit connected to the base terminal of the first transistor to drive the first transistor, the first drive circuit comprising a resistive component having a resistance value (R34); a second transistor having a second gain (hFE2) and configured to alternately operate between a conductive state and a non-conductive state, wherein the second transistor has a base terminal, a collector terminal, and an emitter terminal; a second drive circuit connected to the base terminal of the second transistor to drive the second transistor; wherein when the first transistor operates in the conductive state, the second transistor operates in the non-conductive state and the first pulse of a waveform cycle of the oscillating power signal is generated and the first integral value of the first pulse is a function of first gain (hFE1); wherein when the second transistor operates in the conductive state, the first transistor operates in the non-conductive state and the second pulse of a waveform cycle of the oscillating power signal is generated and the second integral value of the second pulse is a function of the second gain (hFE2); and wherein the first integral value of the first pulse of each waveform cycle of the power signal is different from the second integral value of the second pulse of each waveform cycle such that is
greater than or equal to a minimum value in order to minimize striations in the at least one lamp.
In a related embodiment, the minimum value may be equal to 1. In another related embodiment, the resistive component may be a resistor connected to the base terminal of the first transistor. In yet another related embodiment, the first drive circuit may further include a diode and a resistor, wherein the diode and the resistive component may be connected together in a series combination, and the series combination of the diode and the resistive component may be connected in parallel with the resistor. In still another related embodiment, the second drive circuit may include a diode and a resistor connected together in parallel. In yet still another related embodiment, the ballast may further include: a rectifier to receive an alternating current (AC) voltage signal and to produce a rectified voltage signal therefrom; and a power factor correction circuit to receive the rectified voltage signal and to provide a corrected voltage signal, wherein the inverter circuit may be connected to the power factor correction circuit and the inverter circuit may be configured to generate the oscillating power signal as a function of the corrected voltage signal.
In still yet another related embodiment, the minimum value may be dependent on an expected ambient temperature for the ballast.
In another embodiment, there is provided a ballast to energize at least one lamp. The ballast includes: an inverter circuit to provide an oscillating power signal to energize the at least one lamp, wherein the oscillating power signal has a waveform cycle comprising a first pulse that has a first integral value and a second pulse that has a second integral value, wherein the inverter circuit includes: a first transistor having a first gain (hFE1) and configured to alternately operate between a conductive state and a non-conductive state, wherein the first transistor has a base terminal, a collector terminal, and an emitter terminal; a first drive circuit connected to the base terminal of the first transistor to drive the first transistor; a second transistor having a second gain (hFE2) and configured to alternately operate between a conductive state and a non-conductive state, wherein the second transistor has a base terminal, a collector terminal, and an emitter terminal; a second drive circuit connected to the base terminal of the second transistor to drive the second transistor, the second drive circuit comprising a resistive component having a resistance value (R34); wherein when the first transistor operates in the conductive state, the second transistor operates in the non-conductive state and the first pulse of a waveform cycle of the oscillating power signal is generated and the first integral value of the first pulse is a function of first gain (hFE1); wherein when the second transistor operates in the conductive state, the first transistor operates in the non-conductive state and the second pulse of a waveform cycle of the oscillating power signal is generated and the second integral value of the second pulse is a function of the second gain (hFE2); and wherein the first integral value of the first pulse of each waveform cycle of the oscillating power signal is different from the second integral value of the second pulse of each waveform cycle such that
is greater than or equal to a minimum value in order to minimize striations in the at least one lamp.
In a related embodiment, the minimum value may be equal to 1. In another related embodiment, the second drive circuit may further include a diode and a resistor, wherein the diode and the resistive component may be connected together in a series combination, and the series combination of the diode and the resistive component may be connected in parallel with the resistor. In still another related embodiment, the first drive circuit may include a diode and a resistor connected together in parallel. In yet another related embodiment, the ballast may further include: a rectifier to receive an alternating current (AC) voltage signal and to produce a rectified voltage signal therefrom; and a power factor correction circuit to receive the rectified voltage signal and to provide a corrected voltage signal, wherein the inverter circuit may be connected to the power factor correction circuit and the inverter circuit may be configured to generate the oscillating power signal as a function of the corrected voltage signal. In still yet another related embodiment, the minimum value may be dependent on an expected ambient temperature for the ballast.
The foregoing and other objects, features and advantages disclosed herein will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles disclosed herein.
The ballast 104 includes at least one high voltage input terminal (i.e., line voltage input terminal) 108 adapted for connecting to the alternating current (AC) power supply (e.g., standard 120V AC household power), a neutral input terminal 110, and a ground terminal 112 connectable to ground potential. An input AC power signal is received by the ballast 104 from the AC power supply via the high voltage input terminal 108. The ballast 104 includes an electromagnetic interference (EMI) filter and a rectifier (e.g., full-wave rectifier) 114, which are illustrated together in
A power factor correction circuit 120, which may, in some embodiments, be a boost converter, is connected to the first and second output terminals of the EMI filter and rectifier 114. The power factor correction circuit 120 receives the rectified DC voltage (VRectified) and produces a high DC voltage (VBoost) on a high DC voltage bus (“high DC bus”) 122. A shunt capacitor C14 is connected across the output of the power factor correction circuit 120. An inverter circuit 126 has an input connected to the power factor correction circuit 120 for receiving the high DC voltage (VBoost) from the power factor correction circuit 120. The inverter circuit 126 is configured to convert the high DC voltage (VBoost) from the power factor correction circuit 120 to an oscillating power signal for supplying to the lamp 106.
In
A starting circuit is connected between the base and emitter terminals of the second switching component Q3. The starting circuit includes a diode for alternating current (DIAC) D15, a resistor R15, and a capacitor C8. The DIAC D15 has a predetermined breakover voltage. When a voltage at an input to the DIAC D15 (i.e., a voltage across the capacitor C8) increases to the predetermined breakover voltage, the DIAC D15 switches from operating in a non-conductive mode to operating in a conductive mode. As such, the DIAC D15 conducts a startup pulse to the second switching component Q3 to initiate switching operations. In
Once the second switching component Q3 is initially turned on via the starting circuit, the inverter circuit 126 operates in a normal operating mode wherein the first and second switching components, Q2 and Q3, are complementarily commutated via the first and second drive circuits. In other words, the first and second switching components, Q2 and Q3, are operated such that when the first switching component Q2 is conductive (e.g., ON), the second switching component Q3 is non-conductive (e.g., OFF). Likewise, when the second switching component Q3 is conductive (e.g., ON), the first switching component Q2 is non-conductive (e.g., OFF). The inverter circuit 126 includes a conduction control circuit for preventing the DIAC D15 from conducting during the normal operating mode. The conduction control circuit includes a diode D11, a diode D6, a resistor R26, and a resistor R27. The diode D11 is connected in parallel with the DIAC D15. The resistor R27 and the resistor R26 are connected together in series between the cathode of the diode D11 and the collector terminal of the second switching component Q3. The diode D6 is connected in parallel with the series connected resistors, R26 and R27, such that the anode of the diode D6 is connected to the cathode of the diode D11, and the cathode of the diode D6 is connected to the collector terminal of the second switching component Q3.
The inverter circuit 126 includes a transformer providing the oscillating power to the lamp 106. In particular, a primary winding T1 of the transformer is connected to the collector terminal of the second switching component Q3. A secondary winding T1A of the transformer is configured for connecting in series with the lamp 106. A current limiting capacitor C9 is also connected in series with the lamp 106, between the secondary winding T1A of the transformer and the lamp 106, in order to limit the current received by the lamp 106. In embodiments wherein the ballast/lamp system 100 powers a plurality of lamps, each lamp is connecting in series with a corresponding current limiting capacitor, between the secondary winding T1A of the transformer and the return terminal J8. As such, each of the pairs of a series-connected lamp and a corresponding current limiting capacitor are connected together in parallel. In
As described above, in
Referring again to
As such, the first transistor Q2 and the second transistor Q3 are selected and/or designed so that the first gain hFE1 and the second gain hFE2 have particular values governed by equation 1.
In some embodiments, the minimum value is dependent on an expected ambient temperature where the ballast will be used. In particular, as the expected ambient temperature decreases, the minimum value increases. For example, a minimum value of 1 as expressed above in equation 1 may be used when the expected ambient temperature is around 21 degrees Celsius. On the other hand, a minimum value of 2 may be used when the expected ambient temperature is around 8 degrees Celsius.
In one example, the first and second transistors, Q2 and Q3, are selected from a plurality of transistors having a range of gains. The plurality of transistors having the range of gains can be characterized as transistors having a high gain of around 46, transistors having a medium gain of around 34, and transistors having a low gain of around 22. The resistor R34 can be selected to have a resistance of approximately 1 Ohm or approximately 2 Ohms. In accordance with this example, the first transistor Q2, the second transistor Q3, and the resistor R34 are selected so that the first gain hFE1, the second gain hFE2, and the resistance R34 have particular values governed by equation 2.
In one example, the first and second transistors, Q2 and Q3, are selected from a plurality of transistors having a range of gains. The plurality of transistors having the range of gains can be characterized as transistors having a high gain of around 46, transistors having a medium gain of around 34, and transistors having a low gain of around 22. The resistor R34 can be selected to have a resistance of approximately 1 Ohm or approximately 2 Ohms. In accordance with this example, the first transistor Q2, the second transistor Q3, and the resistor R34 are selected so that the first gain hFE1, the second gain hFE2, and the resistance R34 have particular values governed by equation 3.
As described above in connection with ballast/lamp system 100 and equation 1, the minimum value may be dependent on the expected ambient temperature where the ballast will be used. More specifically, the minimum value is increased as the expected ambient temperature is decreased. Thus, in one example, the minimum value of 1 as set forth in equations 2 and 3 may be selected when the expected ambient temperature is around 21 degrees Celsius. However, instead, a minimum value of 2 may be used in equations 2 and 3 when the expected ambient temperature is around 8 degrees Celsius.
Unless otherwise stated, use of the word “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems.
Throughout the entirety of the present disclosure, use of the articles “a” and/or “an” and/or “the” to modify a noun may be understood to be used for convenience and to include one, or more than one, of the modified noun, unless otherwise specifically stated. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, may be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein.
Although the methods and systems have been described relative to a specific embodiment thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, may be made by those skilled in the art.
The present application claims priority of U.S. Provisional Application No. 61/426,282, filed Dec. 22, 2010, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61426282 | Dec 2010 | US |
