Electronic ballast with inverter control circuit
First Claim
1. An electronic ballast for powering at least one gas discharge lamp having a pair of heatable filaments, comprising:
- an inverter, comprising;
first and second input terminals for receiving a source of input power, wherein the second input terminal is coupled to a circuit ground node;
an inverter output terminal;
a first inverter switch coupled between the first input terminal and the inverter output terminal;
a second inverter switch coupled between the inverter output terminal and a first node; and
an inverter control circuit coupled to the first and second inverter switches, and operable to commutate the inverter switches at a drive frequency, the inverter control circuit having a plurality of fault detection inputs and a DC supply input for receiving operating power;
a resonant output circuit coupled to the inverter output terminal, the resonant output circuit having a natural resonant frequency and a plurality of output wires coupleable to the lamp;
a lamp fault detection circuit coupled between the first node, at least one of the output wires, and the fault detection inputs of the inverter control circuit, the lamp fault detection circuit being operable to provide fault detection signals to the fault detection inputs to indicate whether or not a lamp fault condition is present; and
wherein the inverter control circuit is further operable to provide;
(a) a filament preheating mode wherein the drive frequency is maintained at a preheat frequency for a predetermined preheating period;
(b) a frequency shifting mode wherein the drive frequency is shifted from the preheat frequency to an operating frequency;
(c) a high-power operating mode wherein the drive frequency is maintained at the operating frequency in response to successful ignition and normal operation of the lamp within a predetermined ignition period, followed by continued normal operation of the lamp after ignition;
(d) a repeating mode wherein the filament preheating and frequency shifting modes are repeated up to a predetermined number of times in response to each of;
(i) failure of the lamp to ignite and operate normally within the predetermined ignition period when both lamp filaments are intact and properly connected to the output wires; and
(ii) failure of the lamp to operate normally after igniting; and
(e) a low-power protection mode wherein the drive frequency is set at the preheat frequency in response to each of;
(i) the lamp being disconnected from the ballast; and
(ii) the lamp failing to ignite and operate normally within the predetermined ignition period after the repeating mode has been carried out the predetermined number of times.
3 Assignments
0 Petitions
Accused Products
Abstract
An electronic ballast (300) for powering at least one gas discharge lamp (10) includes an inverter (400), an output circuit (700), a lamp fault detection circuit (800), and an inverter control circuit (500). Ballast (300) operates according to an inverter control method (100) that includes repeating a filament preheating step and a frequency shifting step up to a predetermined number of times in order to facilitate lamp ignition under low-temperature conditions and to verify the legitimacy of a lamp fault. Inverter control circuit (500) is well-suited for implementation as a custom integrated circuit. Ballast (300) optionally includes an overcurrent detection circuit (820'"'"') with an adjustable lamp fault detection threshold that provides decreased sensitivity during lamp starting and enhanced protection after lamp ignition.
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Citations
31 Claims
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1. An electronic ballast for powering at least one gas discharge lamp having a pair of heatable filaments, comprising:
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an inverter, comprising; first and second input terminals for receiving a source of input power, wherein the second input terminal is coupled to a circuit ground node; an inverter output terminal; a first inverter switch coupled between the first input terminal and the inverter output terminal; a second inverter switch coupled between the inverter output terminal and a first node; and an inverter control circuit coupled to the first and second inverter switches, and operable to commutate the inverter switches at a drive frequency, the inverter control circuit having a plurality of fault detection inputs and a DC supply input for receiving operating power; a resonant output circuit coupled to the inverter output terminal, the resonant output circuit having a natural resonant frequency and a plurality of output wires coupleable to the lamp; a lamp fault detection circuit coupled between the first node, at least one of the output wires, and the fault detection inputs of the inverter control circuit, the lamp fault detection circuit being operable to provide fault detection signals to the fault detection inputs to indicate whether or not a lamp fault condition is present; and wherein the inverter control circuit is further operable to provide; (a) a filament preheating mode wherein the drive frequency is maintained at a preheat frequency for a predetermined preheating period; (b) a frequency shifting mode wherein the drive frequency is shifted from the preheat frequency to an operating frequency; (c) a high-power operating mode wherein the drive frequency is maintained at the operating frequency in response to successful ignition and normal operation of the lamp within a predetermined ignition period, followed by continued normal operation of the lamp after ignition; (d) a repeating mode wherein the filament preheating and frequency shifting modes are repeated up to a predetermined number of times in response to each of;
(i) failure of the lamp to ignite and operate normally within the predetermined ignition period when both lamp filaments are intact and properly connected to the output wires; and
(ii) failure of the lamp to operate normally after igniting; and(e) a low-power protection mode wherein the drive frequency is set at the preheat frequency in response to each of;
(i) the lamp being disconnected from the ballast; and
(ii) the lamp failing to ignite and operate normally within the predetermined ignition period after the repeating mode has been carried out the predetermined number of times. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An electronic ballast for powering at least two gas discharge lamps, each lamp having a pair of heatable filaments, the ballast comprising:
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an inverter, comprising; first and second input terminals for receiving a source of input power, wherein the second input terminal is coupled to a circuit ground node; an inverter output terminal; a first inverter switch coupled between the first input terminal and the inverter output terminal; a second inverter switch coupled between the inverter output terminal and a first node; and an inverter control circuit coupled to the first and second inverter switches, and operable to commutate the inverter switches at a drive frequency, the inverter control circuit having a plurality of fault detection inputs and a DC supply input for receiving operating power; a resonant output circuit coupled to the inverter output terminals, the resonant output circuit having a natural resonant frequency and a plurality of output wires coupleable to the lamps; a lamp fault detection circuit coupled between the first node, at least one of the output wires, and the fault detection inputs of the inverter control circuit, the lamp fault detection circuit being operable to provide fault detection signals to the fault detection inputs to indicate whether or not a lamp fault condition is present; and wherein the inverter control circuit is further operable to provide; (a) a filament preheating mode wherein the drive frequency is maintained at a preheat frequency for a predetermined preheating period; (b) a frequency shifting mode wherein the drive frequency is shifted from the preheat frequency to an operating frequency; (c) a high-power operating mode wherein the drive frequency is maintained at the operating frequency in response to successful ignition and normal operation of all of the lamps within a predetermined ignition period, followed by continued normal operation of all of the lamps after ignition; (d) a repeating mode wherein the filament preheating and frequency shifting modes are repeated up to a predetermined number of times in response to each of;
(i) failure of at least one of the lamps to ignite and operate normally within the predetermined ignition period when all lamp filaments are intact and properly connected to the output wires; and
(ii) failure of at least one of the lamps to operate normally after igniting; and(e) a low-power protection mode wherein the drive frequency is set to the preheat frequency in response to each of;
(i) at least one of the lamps being disconnected from the ballast; and
(ii) at least one of the lamps failing to ignite and operate normally within the predetermined ignition period after the repeating mode has been carried out the predetermined number of times. - View Dependent Claims (27, 28, 29, 30)
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31. An electronic ballast for powering at least two gas discharge lamps, comprising:
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an inverter, comprising; first and second input terminals adapted to receive a source of input power, wherein the second input terminal is coupled to a circuit ground node; an inverter output terminal; a first inverter switch coupled between the first input terminal and the inverter output terminal; a second inverter switch coupled between the inverter output terminal and a first node; and an inverter control circuit comprising a first drive output coupled to the first inverter switch, a second drive output coupled to the second inverter switch, a reference output coupled to the inverter output terminal, a DC supply input, a no-load detect (NLD) input, and an overcurrent detect (OCD) input; an output circuit, comprising; a set of output wires comprising first, second, third, fourth, fifth, and sixth output wires adapted to being coupled to at least a first and a second gas discharge lamp, wherein the first output wire is coupleable to the second output wire through a first filament of the first lamp, the third output wire is coupleable to the fourth output wire through a second filament of the first lamp, the second filament of the first lamp is coupleable in parallel with a first filament of the second lamp, and the fifth output wire is coupleable to the sixth output wire through a second filament of the second lamp; a resonant inductor coupled between the inverter output terminal and the first output wire; a resonant capacitor coupled between the first and sixth output wires; a DC blocking capacitor coupled between the sixth output wire and the circuit ground node; a first filament path resistor coupled between the second and third output wires; a second filament path resistor coupled between the fourth and fifth output wires; a first filament heating circuit coupled between the first and second output wires; a second filament heating circuit coupled between the third and fourth output wires; and a third filament heating circuit coupled between the fifth and sixth output wires; a no-load detection circuit coupled between the sixth output wire and the NLD input of the inverter control circuit; an overcurrent detection circuit coupled between the first node and the OCD input of the inverter control circuit; and wherein the inverter control circuit further comprises; a first comparator having an inverting input coupled to the NLD input, a non-inverting input coupled to a fault reference voltage, and an output; a second comparator having a non-inverting input coupled to the OCD input, an inverting input coupled to the fault reference voltage, and an output; a protection logic circuit having a plurality of logic inputs and a logic output, wherein the plurality of logic inputs includes a first logic input coupled to the output of the first comparator, a second logic input coupled to the output of the second comparator, a timer reset input, a power-up reset input, and a repeat disable input; wherein the protection logic circuit is operable to provide at its logic output; (a) a logic "0" in response to a logic "0" being present at all of the logic inputs; and (b) a logic "1" in response to a logic "1" being present at at least one of;
(i) the first logic input;
(ii) the second logic input;
(iii) the power-up reset input; and
(iv) the repeat disable input;a preheat timing circuit, comprising; a DC current source coupled between the DC supply input and a second node; a timing capacitor coupled between the second node and the circuit ground node, and having a timing capacitor voltage; and a discharge switch coupled in parallel with the timing capacitor and having a control lead coupled to the logic output of the protection logic circuit; a preheat timer comparator having a non-inverting input coupled to the second node, an inverting input coupled to a preheat timing reference voltage, and an output; an ignition timer comparator having a non-inverting input coupled to the second node, an inverting input coupled to an ignition timing reference voltage, and an output; a preheat reset comparator having a non-inverting input coupled to the second node, an inverting input coupled to a timer reset reference voltage, and an output coupled to the timer reset input of the protection logic circuit; a power-up reset circuit, comprising; a triggering resistor coupled between the DC supply input and a third node; a triggering capacitor coupled between the third node and the circuit ground node; and a one-shot circuit coupled between the third node and the power-up reset input of the protection logic circuit, and operable to provide a momentary voltage pulse at the power-up reset input in response to the voltage at the third node reaching a predetermined trigger threshold following application of power to the ballast; a counter circuit, comprising; a clock input coupled to the output of the preheat timer comparator; a first reset input coupled to the output of the ignition timer comparator; a second reset input coupled to the output of the First comparator; a third reset input coupled to the pulse output of the power-up reset circuit; and a counter output coupled to the repeat disable input of the protection logic circuit; a driver circuit coupled to the first and second drive outputs and the reference output of the inverter control circuit, and operable to provide complementary switching of the first and second inverter switches at the drive frequency, the driver circuit including a first input and a second input; a frequency-determining resistance coupled between the first and second inputs of the driver circuit; a frequency-determining capacitance coupled between the second input of the driver circuit and the circuit ground node; and a frequency sweep circuit coupled between the output of the preheat timer comparator and the second input of the driver circuit, and operable to effectively augment the frequency-determining capacitance of the inverter driver circuit in response to a logic "1" being present at the output of the preheat timer comparator.
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Specification