Patent Grant
8581497
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates generally to electronic ballasts and associated methods for powering lighting sources such as fluorescent lamps. More particularly, the present invention relates to an electronic ballast having circuitry for detecting the presence or removal of one or more common lamp filaments and regulating the performance of an associated output stage accordingly.
Dimming ballasts are generally desirable for, among other things, light output control and associated energy savings. If a conventional dimming ballast has a parallel connection of common lamp filaments it is very difficult to sense removal of one of the common filaments by using DC current or voltage sensing procedures as are currently known in the art. This is a primary reason why most dimming ballasts do not shut down when a common filament is removed from the ballast, meaning that there is a distinct possibility for a technician to get shocked by open circuit voltage when re-lamping. If the open circuit voltage is sufficiently high, the ballast may fail safety tests for issues such as through-lamp leakage.
In an embodiment of the present invention, an electronic ballast is provided with circuitry for detecting the removal of one or more lamp filaments across a range of dimming levels, and regulating an output stage including at least first and second pairs of lamp connection output terminals based on a filament connection status. A filament removal sensing circuit is coupled to the output terminal pairs and configured to generate an output voltage representative of a filament connection status with respect to the output terminal pairs. A microcontroller is coupled to receive the output voltage from the filament removal sensing circuit and programmed to determine a rate of change in the output voltage, compare the rate of change in the output voltage to a predetermined threshold value, and disable the output stage when the rate of change in the output voltage exceeds the predetermined threshold value.
In another embodiment, an electronic ballast according to the present invention includes an output stage with at least first, second and third pairs of lamp connection output terminals. A first filament removal sensing circuit is coupled to the first and second output terminal pairs and configured to generate an output voltage representative of a first filament connection status, and a second filament removal sensing circuit is coupled to the second and third output terminal pairs and configured to generate an output voltage representative of a second filament connection status. A controller receives the output voltages from the first and second filament removal sensing circuits and is programmed to determine a rate of change for each of the respective output voltages, compare the determined rates of change in the output voltages to a predetermined threshold value, and disable the output stage when one or more of the rates of change in the output voltages exceeds the predetermined threshold value.
Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” may include plural references, and the meaning of “in” may include “in” and “on.” The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may.
The term “coupled” means at least either a direct electrical connection between the connected items or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means at least either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function. The term “signal” as used herein may include any meanings as may be understood by those of ordinary skill in the art, including at least an electric or magnetic representation of current, voltage, charge, temperature, data or a state of one or more memory locations as expressed on one or more transmission mediums, and generally capable of being transmitted, received, stored, compared, combined or otherwise manipulated in any equivalent manner.
Terms such as “providing,” “processing,” “supplying,” “determining,” “calculating” or the like may refer at least to an action of a computer system, computer program, signal processor, logic or alternative analog or digital electronic device that may be transformative of signals represented as physical quantities, whether automatically or manually initiated.
Referring generally to
Referring to
An exemplary topology for an output stage of the ballast 1a as represented in
A first lamp connection branch is coupled to the resonant tank and may be defined by a DC blocking capacitor C1, a first pair of lamp connection output terminals across which a first filament R1a for a first lamp Lamp1 may be coupled, and a second pair of lamp connection output terminals across which a second filament R1b for the first lamp Lamp1 may be coupled.
A second lamp connection branch is also coupled to the resonant tank and may be defined by another DC blocking capacitor C2, a third pair of lamp connection output terminals across which a first filament R2a for a second lamp Lamp2 may be coupled, and the second pair of lamp connection output terminals as shared with the first branch and across which a second filament R2b for the second lamp Lamp2 may be coupled in parallel with the second filament R1b for the first lamp Lamp1.
A second frequency controlled AC voltage source Vac1(f) may further be provided to drive filament heating. The frequency of the second voltage source Vac1(f) can be modified such that the voltage across a primary winding Tp of a filament heating transformer can be adjusted, as well as the voltage across a plurality of auxiliary (secondary) windings including a first auxiliary winding Ts1 for heating filament R1a, a second auxiliary winding Ts2 for heating filament R2a and a third auxiliary winding Ts3 for heating filaments R1b and R2b. A resonant capacitor C3 is coupled in series with the primary winding Tp.
Control circuitry 10 is used to adjust the frequency of the first and second voltage sources Vac(f) and Vac1(f) according to an input dimming control signal. The terms “control circuit” or “controller” as used herein may refer to at least a microcontroller, a general microprocessor, an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array, or various alternative blocks of discrete circuitry as known in the art, designed to perform functions as further defined herein.
The exemplary topology for an electronic ballast 1a as described above and represented in
The common (yellow) filaments R1b, R2b of the two lamps, respectively, as shown in
In an embodiment of the present invention as represented in
In another embodiment of an electronic ballast topology 1b as represented in
The structure and operation of the respective filament removal sensing circuits 18, 22, 26 may differ with respect to their application in a parallel- or series-configured ballast topology, but otherwise may be described in equivalent fashion below.
Referring again to the first filament removal sensing circuit 18 in the embodiment shown in
In a normal low level dimming condition, most of the lamp current passes through the lamp (using Lamp1 for this example) because the lamp impedance is substantially lower than the impedance of the diode D15 in series with capacitor C6 and resistor R3. The voltage across the capacitor C10 would be small or close to zero depending on the ratio between capacitors C1 and Cdc.
When a common filament is removed (for example, the common filament R1b of Lamp1) from the output stage, the lamp stops conducting current immediately such that all of the current has to be bypassed by the first filament removal sensing circuit 18. The impedance of capacitor C6 and resistor R3 can be set much lower than that of the first branch (i.e., R6, R5, C10) wherein a large positive voltage appears across the first filament removal sensing circuit 18 generally, and more particularly across capacitor C10.
Referring to
As shown in
Referring now to
The controller begins by starting an internal ADC timer (step 61) to count off a particular time period t(k).
The filament removal sensing circuit generates an output voltage V_C10 representative of a filament status for a common lamp filament to which the circuit is coupled. The controller then receives the output voltage V_C10 from the filament removal sensing circuit (and further V_C11 where the second filament removal sensing circuit is present) and performs an ADC conversion for each timer period t(k) (step 62).
An output voltage for a first (e.g., immediately preceding) time period V_C10(k−1) is compared to the output voltage for a second (e.g., current) time period V_C10(k) (step 63).
If a difference between the second (current) output voltage V_C10(k) and the first (immediately preceding) output voltage V_C10(k−1) is determined to be less than a predetermined threshold value dv (i.e., “no” in response to the query of step 64), then a calculated rate of change for the output voltage may be determined as less than a predetermined rate of change threshold value, consistent with a first filament status of being coupled to the ballast, and the process returns to step 62.
If the difference between the second (current) output voltage V_C10(k) and the first (immediately preceding) output voltage V_C10(k−1) is determined to be greater than the predetermined threshold value dv (i.e., “yes” in response to the query of step 64), then the calculated rate of change for the output voltage may be determined as greater than a predetermined rate of change threshold value, consistent with a second filament status wherein the common filament is removed from the ballast. The process continues to step 65, wherein the controller disables the first voltage source Vac(f) and the second voltage source Vac1(f), effectively disabling the lamp tank and the filament drive tank of the electronic ballast.
The controller may then execute a re-lamp sensing routine (step 66) to determine when a lamp has been properly positioned with respect to the lamp output connection terminals, after which the first voltage source Vac(f) and the second voltage source Vac1(f) are enabled, effectively enabling the lamp tank and the filament drive tank of the electronic ballast.
In an embodiment (not shown) the method may further include steps for switching a flag or an equivalent between a first state associated with a first filament status and a second state associated with a second status. The controller may set the flag from the first state to a second state upon disabling the lamp tank and the filament drive tank. When a filament connected status has been detected pursuant to the re-lamp routine and the tanks enabled, the controller may be further programmed to set the flag from the second state to the first state, wherein the controller returns to executing the method in the manner initially described above.
The previous detailed description has been provided for the purposes of illustration and description. Thus, although there have been described particular embodiments of the present invention of a new and useful “Electronic Ballast and Method for Detecting Lamp Filament Removal in Low Level Dimming Conditions,”it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.
This application claims benefit of the following patent application(s) which is/are hereby incorporated by reference: U.S. Provisional Application No. 61/529,108, dated Aug. 30, 2011.
| Number | Name | Date | Kind |
|---|---|---|---|
| 20050035729 | Lev et al. | Feb 2005 | A1 |
| 20100301754 | Bakre et al. | Dec 2010 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 61529108 | Aug 2011 | US |
