Abstract: A glass extension (24) with a cavity (32) for an amalgam (22) is added to an exhaust tube (12) or a flare (14) of a fluorescent lamp. The mouth (36) of the cavity (32) is provided with a bimetal valve having a cover portion (40) to close the cavity (32) when the lamp is cold and to open the cavity when the lamp is hot. The amalgam (22) is a metallic amalgam of, for example, mercury or other know suitable materials for establishing a metallic vapor equilibrium during operation of a discharge lamp. The amalgam holder helps to maintain optimum mercury vapor equilibrium at start-up, and to reduce the effects of mercury vapor starvation resulting from off-times.

Abstract: An amalgam is accurately placed and retained in an optimized location in the exhaust tube of an electrodeless SEF lamp for operation at a mercury vapor pressure in the optimum range from approximately four to seven millitorr by forming a dimple in the exhaust tube and using a dose locating member to locate and retain the amalgam on the side of the dimple away from the core of the lamp after filling the lamp. As an alternative, two dimples may be situated on opposite sides of the exhaust tube for performing the same function as, but with less depth than, the single dimple. In another alternative embodiment, first and second dimple configurations are formed in the exhaust tube after tip-off thereof, each dimple configuration including either one or two dimples. The second dimple configuration is spaced apart from the first dimple configuration along the length of the exhaust tube.

Abstract: An electrically controllable variable capacitor includes the interelectrode capacitance of at least one power MOSFET, a capacitance connected in series with the MOSFET and having one terminal connected to the drain or source thereof (the series capacitance), and bias control circuitry for controlling the bias voltage applied to the MOSFET. The voltage rating of the MOSFET, the peak amplitude of the applied ac signal, and the value of the series capacitance determine the range of dc bias voltages over which the MOSFET can be operated, and hence the capacitance range of the variable capacitor. Such a variable capacitance is useful as a tuning capacitor in an electrodeless HID lamp ballast.

Abstract: An amalgam is accurately placed and retained in an optimal location near the cold spot of an electrodeless SEF lamp for operation at a mercury vapor pressure in the optimum range from approximately four to seven millitorr. The amalgam is positioned at the tip of an extended exhaust tube near the apex of the lamp envelope by forming an indentation in the exhaust tube and, in some embodiments, a dose locating member in combination therewith. An evacuation hole is formed below the indentation for evacuation of the lamp envelope, or bulb, during lamp fabrication. In an alternative embodiment, the extension of the exhaust tube is situated perpendicular to the main portion of the tube to allow for lateral adjustment of the position of the amalgam, thereby allowing for even further control of the amalgam operating temperature.

Abstract: An electrodeless SEF fluorescent discharge lamp of the type having an envelope with a re-entrant cavity formed therein for containing an excitation coil includes an amalgam positioned for maintaining an optimum mercury vapor pressure during lamp operation. An exhaust tube extending through the re-entrant cavity has an extension into the envelope toward the apex of the lamp envelope. The exhaust tube extension has a rim portion for holding an amalgam support in position within the lamp envelope. The amalgam support preferably comprises a wire wrapped about and held in place by the rim portion. At the other end of the wire, an amalgam is wetted to a wire screen or helical wire structure at a predetermined optimal location within the lamp envelope. Alternatively, two amalgams are supported by the amalgam support at predetermined optimal locations for starting and steady-state operation of the lamp, respectively.

Abstract: An excitation coil for an electrodeless fluorescent lamp of the type having a core of insulating material, is made of a metal having a low thermal expansion coefficient which is plated with a high-conductivity metal. An insulating coating is applied over the metal plating. An exemplary coil includes a molybdenum wire, plated with silver, and finally coated with alumina. The result is a thermally stable excitation coil that maintains its shape, even at high operating temperatures, and hence maintains its impedance characteristic over the operating range of the lamp.

Abstract: A low-inductance package for multiple paralleled devices includes an electrically insulating substrate having three power terminals direct-bonded to the upper surface thereof and a conductive pad direct-bonded to the lower surface thereof for connection to a heat sink. Two groups of multiple parallel-coupled devices are each soldered to one of the three power terminals and are further connected in a half-bridge configuration such that one of the three power terminals is common to both groups of devices. The package further includes a pair of first Kelvin terminals, i.e., a first Kelvin control terminal and a first Kelvin source terminal, and a pair of second Kelvin terminals, i.e., a second Kelvin control terminal and a second Kelvin source terminal. The Kelvin terminals are soldered to the appropriate power terminals, depending upon the particular circuit configuration.

Abstract: A variable capacitor includes a fixed conductive plate and a movable conductive plate with a dielectric disposed between them. A piezoelectric actuator is used to vary the distance between the conductive plates by moving the movable plate with respect to the fixed plate, with capacitance changing in inverse proportion to distance moved. In an electrodeless high intensity discharge lamp ballast, such a variable capacitor is situated in series with the excitation coil of the lamp. When a control voltage is applied to the piezoelectric actuator, the movable plate is moved from a starting position to a running position so as to maintain the ballast load in tune under both starting and running conditions, respectively, resulting in higher efficiency operation.

Abstract: A closed-loop control system for a Class-D power amplifier circuit, having a variable output resonant circuit impedance, maintains high-efficiency operation by using the phase angle between the resonant load voltage and current to control tuning of the resonant circuit. The resonant load circuit voltage and current are supplied to a phase detector for detecting the phase angle therebetween and for generating a voltage proportional thereto. The output voltage from the phase detector is compared to a reference voltage by an error amplifier. The resulting error voltage is employed as the input signal to control circuitry for tuning the output resonant circuit. Such a control system is suitable for maintaining high-efficiency operation of an electrodeless high intensity discharge lamp system.

Abstract: A high-frequency capacitor includes first and second conductive members, each having a plurality of U-shaped metal plates disposed parallel to each other and a terminal plate coupled between the ends thereof. The metal plates of the first and second conductive members are interleaved, and a dielectric material is disposed between the adjacent metal plates. The result is a low-inductance capacitor suitable for use in a high-frequency electronic circuit, such as an electrodeless high intensity discharge (HID) lamp ballast. Furthermore, such acapacitor may be suitably integrated with a heat sink in an electrodeless HID lamp ballast.

Abstract: A ballast for an electrodeless high intensity discharge lamp comprises a Class-D power amplifier including an integrated tuning capacitor network and heat sink. A series blocking/tuning capacitor and a parallel tuning capacitor are integrated by sharing a common capacitor plate. The metal plates of the parallel tuning capacitor also comprise heat sink planes to remove excess heat from the excitation coil of the lamp. Heat sink fins are affixed to the plates of the parallel capacitor. Efficiency is maximized by matching the impedance of the ballast load network.

Abstract: A lamp ballast configuration in which input power is conducted by one circuit board to the switching devices of a half bridge circuit whose output is conducted on a second circuit board with the two circuit boards mounted parallel and spaced apart disposes the device package which extends between the two circuit boards in an exposed position for direct contact to a heat sink. Drive transformers for the switching devices are preferably mounted between the circuit boards and shielded on four of their six sides by a combination of ground planes on the circuit boards and wide, flat ground conductors connecting the ground planes of the two circuit boards. A compact, high efficiency (>91%) RF system is obtained which is suitable for excitation of an electrodeless, high-intensity-discharge lamp.

Abstract: A power factor correction circuit employs a metal oxide varistor in series with a filter capacitor. The varistor provides a low-impedance path for pre-charging the filter capacitor, thus enabling the avoidance of high inrush current to circuit devices, while the filter capacitor energizes the circuit when the capacitor voltage exceeds the AC source voltage. The circuit is insensitive to normal line transients. One application is for use in a gas discharge lamp ballast.

Abstract: A pair of starting electrodes are provided for an electrodeless high-intensity-discharge lamp of the type having an arc tube situated within the bore of an excitation coil and in the interior of which tube is to be provided a plasma arc discharge driven by the excitation coil. Each of the starting electrodes is a conductive ring actuated by a piezoelectric bender to move from a normal rest position away from the arc tube to a starting portion disposed adjacent to an associated one of an opposed pair of envelope surfaces. A high-voltage pulse coupled between the starting electrodes causes an electric field to be produced sufficient to create a glow discharge in the arc tube, and cause an almost instantaneous transition to a high-current solenoidal discharge to form the discharge plasma responsive to the normal field provided by the excitation coil; thereafter, the benders are de-activated and the starting electrodes move back to the rest positions.

Abstract: A power line communications (PLC) system utilizes a single conductor of a multiple-conductor power-transmission circuit, for carrying signal current, injected by at least one transmitter in series with that single conductor, to at least one receiver also coupled to that power line circuit. Each transmitter includes a saturable AC coupler connecting a switch to the conductor, while providing DC isolation therebetween. Each transmitter provides a signaling current having a frequency at least two orders of magnitude greater than the power line frequency, during at least some portion of each power line waveform signal cycle when the coupler is not saturated. Each transmitter preferably includes a power supply for providing transmitter operating potential responsive to the load current carried in that single conductor utilized for system signaling.

Abstract: A switched AC ballast is operated synchronously with the AC line during normal running of a gas discharge lamp to limit EMI and is locked in a single phase during start-up (i.e. ignition, glow mode and warm-up) to protect the bridge switches from high voltage starting signals. Devices having a high impedance control input, such as FETs, are employed in the switching bridge thus allowing control of the upper devices in the bridge without a floating power supply. A control circuit insures proper operation of the bridge switches during all operating modes of the discharge lamp.