Ignition scheme for a high intensity discharge lamp
AssigneePhilips Electronics North America Corporation
InventorsMichael Shone, Phuong Huynh
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Abstract
An electronic ballast for reducing blackening of a high intensity discharge lamp, reducing stress on both the lamp and ballast components caused by excessive voltage and current flow and increasing the lamp's effective life. These advantages are achieved through a ballast controller which readjusts the operating frequency of the lamp during each of the three phases of lamp start-up to limit lamp voltage to a predetermined level.
Claims21
An electronic ballast for starting a high intensity discharge lamp having breakdown, non-thermionic glow and thermionic arc phases prior to entering a steady state operating mode, comprising:
- a resonant ignitor for applying a lamp voltage across the lamp;
- an exciter, responsive to a varying control signal, for exciting the resonant ignitor at a varying operating frequency;
- and
- a controller for producing the varying control signal based on the phase of the lamp;
- wherein prior to breakdown the controller adjusts the control signal so as to decrease the operating frequency so as to sweep toward a lamp voltage equal to a predetermined ignition voltage and wherein upon entering the glow phase the controller further adjusts the control signal so as to minimize the time duration within the glow phase and wherein upon entering the thermionic arc phase the controller further adjusts the control signal so as to increase lamp current.
A method of starting a high intensity discharge lamp having breakdown, non-thermionic glow and thermionic arc phases prior to entering a steady state operating mode by a ballast which includes a resonant ignitor for applying a lamp voltage across the lamp, an exciter, responsive to a varying control signal, for exciting the resonant ignitor at a varying operating frequency, and a controller for producing the varying control signal based on the phase of the lamp, comprising:
- decreasing the operating frequency of the exciter so as to sweep toward a lamp voltage equal to a predetermined ignition voltage;
- adjusting the control signal following breakdown so as to minimize the duration of the glow phase time;
- and
- further adjusting the control signal upon entering the thermionic arc phase so as to increase lamp current.
An apparatus for starting a discharge lamp having a breakdown phase, a non-thermionic glow phase and a thermionic arc phase, in that order, prior to entry into a steady state operating mode, comprising:
- a resonant ignitor for applying lamp voltage to the discharge lamp,
- means, responsive to a varying control signal, for generating an alternating voltage at a variable frequency for exciting the resonant ignitor at frequencies determined by the phase of the start-up mode of the discharge lamp, and
- a controller coupled to the voltage generating means for producing the varying control signal based on the phase of the lamp,
- wherein prior to breakdown the controller adjusts the control signal so as to decrease the operating frequency so as to sweep the lamp voltage toward a voltage equal to a predetermined ignition voltage, and wherein upon entering the glow phase the controller further adjusts the control signal so as to further adjust the operating frequency of the resonant ignitor to an optimal frequency f.sub.opt that will optimize the time duration within the glow phase, and wherein upon entering the thermionic arc phase the controller further adjusts the control signal so as to readjust the operating frequency of the resonant ignitor to a frequency that will increase lamp current to an optimal run-up current.
Dependencies are inferred from the claim text.