THERMAL PROTECTION FOR LAMP BALLASTS
First Claim
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1. A circuit for controlling output current from a ballast to a lamp comprising:
- a) a temperature sensing circuit thermally coupled to the ballast to provide a temperature signal having a magnitude indicative of ballast temperature, Th; and
, b) control circuitry capable of causing the ballast to enter a current limiting mode when the magnitude of the temperature signal indicates that Th has exceeded a predetermined maximum desired ballast temperature, T1;
wherein the control circuitry reduces the output current in response to the temperature signal according to one of (i) a step function or (ii) a combination of step and continuous functions, while continuing to operate the ballast.
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Abstract
The output current of a ballast is dynamically limited when an over-temperature condition is detected in the ballast according to one of (i) a step function or (ii) a combination of step and continuous functions, so as to reduce the temperature of the ballast while continuing to operate it.
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Citations
47 Claims
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1. A circuit for controlling output current from a ballast to a lamp comprising:
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a) a temperature sensing circuit thermally coupled to the ballast to provide a temperature signal having a magnitude indicative of ballast temperature, Th; and
,b) control circuitry capable of causing the ballast to enter a current limiting mode when the magnitude of the temperature signal indicates that Th has exceeded a predetermined maximum desired ballast temperature, T1;
wherein the control circuitry reduces the output current in response to the temperature signal according to one of (i) a step function or (ii) a combination of step and continuous functions, while continuing to operate the ballast. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A ballast comprising:
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a) an output circuit that provides output current to a load and having switching circuitry;
b) a reference generator providing reference information concerning a first threshold temperature, T1, for the ballast;
c) a temperature sensitive device to provide ballast operating temperature information, Th;
d) comparison circuitry that provides a first signal having a magnitude indicative of a difference by which Th exceeds T1; and
,e) control circuitry providing a drive signal to the switching circuitry, the control circuitry responsive to the signal provided by the comparison circuitry to adjust at least one of duty cycle, pulse width or frequency of the drive signal so as to alter the output current provided by the ballast according to one of (i) a step function or (ii) a combination of step and continuous functions, while continuing to operate the ballast, when the comparison circuitry indicates that Th is greater than T1. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28)
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29. A thermally protected ballast comprising:
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(a) a front end AC-to-DC converter for receiving a supply voltage;
(b) a back end DC-to-AC converter coupled to the front end AC-to DC converter for providing output current to a load;
(c) a temperature sensitive device adapted to provide a signal indicative of a temperature of the ballast, Tb;
(d) a current limiting circuit providing an output responsive to Th; and
(e) a control circuit responsive to the output of the current limiting circuit, and driving the back end DC-to-AC converter in accordance with the output of the current limiting circuit;
wherein the current limiting circuit causes the control circuit to adjust the output current in response to a detected over-temperature condition, according to one of (i) a step function or (ii) a combination of step and linear functions, while continuing to operate the control circuit. - View Dependent Claims (30, 31, 32)
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33. A method of controlling a ballast comprising the steps of:
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a) measuring ballast temperature, Th;
b) comparing Tb to a first reference, T1;
c) providing an indication of difference between Tb and T1; and
d) controlling output current provided by the ballast according to one of (i) a step function or (ii) a combination of step and continuous functions, while continuing to operate the ballast, in accordance with the result of step (c). - View Dependent Claims (34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44)
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45. A ballast comprising:
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(a) a ballast temperature sensor providing a ballast temperature signal indicative of a ballast temperature;
(b) a foldback protection circuit receiving the ballast temperature signal and providing a foldback protection signal responsive to the ballast temperature signal;
(c) a ballast drive circuit receiving the drive signal and providing at least one switching control signal; and
(d) a DC/AC back end receiving the at least one switching control signal and providing an output current to drive a lamp;
wherein the output current is responsive to the ballast temperature signal according to one of (i) a step function or (ii) a combination of step and continuous functions. - View Dependent Claims (46, 47)
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Specification