Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch cut-out
Reexamination Certificate
1999-01-29
2001-02-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch cut-out
C315S2090CD, C315SDIG007, C315S224000
Reexamination Certificate
active
06194843
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
FIELD OF THE INVENTION
The present invention relates to ballast circuits and more particularly to ballast circuits for energizing high intensity discharge lamps.
BACKGROUND OF THE INVENTION
High intensity discharge (HID) lamps are typically coupled to an electronic ballast which provides an alternating current (AC) signal to the lamps. To initially ignite the lamps, i.e. cold start, the ballast must apply a relatively high voltage, 2 kilovolts for example, which initiates an electric arc between the lamp terminals. After ignition of the lamp, the ballast provides operational signal levels for sustaining the electrical arc which is the source for light emitted by the lamp. To re-ignite a lamp immediately after the arc is extinguished, a hot start voltage, e.g., 10-25 kV, is required which is significantly higher than for cold start of the lamp.
The challenges of achieving hot restart of HID lamps are well known to one of ordinary skill in the art. In general, when the electric arc between the lamp terminals is extinguished the gas within the lamp de-ionizes such that a relatively high restart voltage is required to breakdown the electrical field of the hot gas and re-initiate a light generating arc. Some ballasts utilize a spark gap device to provide voltage levels sufficient to enable hot restart of the lamp. Other ballasts include complex and expensive circuitry to generate the relatively high voltage and current levels needed for hot restart of the lamp. However, such ballasts are often unreliable and may degrade the lamp operating characteristics.
It would, therefore, be desirable to provide a ballast having an efficient and elegant circuit for hot restart of a HID lamp.
SUMMARY OF THE INVENTION
The present invention provides a ballast that includes a circuit for hot restart of a HID lamp. Although the invention is primarily shown and described in conjunction with ballasts for energizing a HID lamp, it is understood that the invention has other applications such as fluorescent lamps, as well as voltage regulators and motors.
In one embodiment, a ballast in accordance with the present invention includes a rectifier and an inverter having a hot restart circuit for providing hot restart of a HID lamp. In one particular embodiment, the inverter includes first and second switching elements coupled in a half bridge configuration. A first control circuit controls the conduction state of the first switching element and a second control circuit controls the conduction state of the second switching element. A resonant circuit including a resonant inductive element and a resonant capacitor is coupled to the switching elements and the lamp for providing an AC signal to the HID lamp.
The hot restart circuit is coupled to the lamp and to the resonant capacitor. In an exemplary embodiment, the hot restart circuit includes inductively coupled first and second inductive elements. A first capacitor is coupled to the second inductive element and a switching element is coupled to the first capacitor. In one particular embodiment, a circuit loop includes the first capacitor, the switching element and the second inductive element. When the switching element transitions to a conductive state, a voltage pulse is generated at the second inductive element. The corresponding signal on the inductively coupled first inductive element is effective to provide hot restart of the lamp.
In one embodiment, the transition of the switching element to a conductive state results in the first capacitor and the second inductive element forming a parallel resonant LC circuit. The resonant signal increases the voltage generated at the second inductive element which concomitantly generates an increased voltage signal on the first inductive element. The resonant nature of the circuit thereby increases signal levels applied to the lamp for enhancing the hot restart capability of the ballast
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International Search Report Mailed May 25, 2000.
Alemu Ephrem
Electro-Mag International, Inc.
Nutter & McClennen & Fish LLP
Wong Don
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