Abstract: An electronic ballast (10) for fluorescent lamps includes a rectifier circuit (100), a boost converter (200), and an inverter (500). The boost converter (200) includes a boost control circuit (400) and a shifting circuit (300). The shifting circuit (300) provides filament preheating by maintaining the boost output voltage at a first level for a predetermined delay period following startup of the boost converter, and then increasing the boost voltage to a second level upon completion of the delay period in order to ignite and operate the lamps. In a preferred embodiment, shifting circuit (300) comprises a shunt circuit (320) and a time delay circuit (360), and inverter (400) is a series resonant half-bridge inverter.

Abstract: A method (100) of controlling an inverter in an electronic ballast for at least one gas discharge lamp protects the inverter from damage due to lamp fault conditions, and provides enhanced noise immunity and multiple ignition attempts for low-temperature lamp starting. The method (100) 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 detected lamp fault.

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.

Abstract: An electronic power supply circuit (50) that includes a rectifying circuit (14), a boost converter (16), an in-rush current reduction circuit (52), and a bulk capacitor (18). The in-rush current reduction circuit (52) includes an in-rush current limiting resistor (54) and a bypass capacitor (56) that are connected in parallel with each other. An improved version of the in-rush current reduction circuit (52) includes a bypass diode (58) connected in parallel with the in-rush current limiting resistor (54) and bypass capacitor (56) which is oriented to provide a path for current flowing out of bulk capacitor (18). One particular application of the disclosed circuit is for use in an electronic ballast for fluorescent lamps.

Abstract: A protection method (10) and protection circuit (500) for protecting an inverter (300) in an electronic preheat ballast (100) for powering at least one fluorescent lamp (902). The inverter (300) includes a first inverter switch (306), a second inverter switch (310), an output circuit (800), and an inverter driver circuit (400) having a drive frequency. The protection circuit (500) comprises a frequency shift circuit (600), a latch circuit (700), a current source network (520), a current sensing circuit (510), and a DC supply capacitance (502). The protection method (10) includes the steps of (a) providing a filament preheat period by initially setting the drive frequency at a first frequency, (b) shifting the drive frequency to a second frequency for igniting and operating the lamps, (c) changing the drive frequency back to the first frequency in response to a lamp fault, and (d) providing, upon correction of the lamp fault, a filament preheat period prior to attempting to ignite and operate the lamps.

Abstract: A transformer (202) has a bobbin (2) which has an inner portion (104) supporting an inner electrical winding (140) and having a magnetic core recess. The inner portion is located within an outer portion (4) supporting an outer electrical winding (40). The inner portion further has an end with a termination connected to the inner winding, an annular recess (126) in which the inner winding is situated, and a channel (132) communicating between the termination end of the inner portion and a remote end of the annular recess. The channel is positioned radially inwardly of the first annular recess and accommodates a portion of the inner winding. By providing the channel radially inwardly of the annular recess, winding wire can extend between the termination end of the inner portion and the remote end of the annular recess across the annular recess without significantly increasing the size of the inner portion and without increasing the gap between the inner and outer portions.

Abstract: An integrated EMI/RFI Filter Magnetic has differential and common mode inductors wound about an I-Core. The I-Core is juxtaposed with an E-Core, with the end surfaces of the E-Core legs facing the I-Core. The magnetic has a substantially closed magnetic path for the differential inductors and the common mode inductors.

Abstract: A parallel resonant converter as disclosed having in one embodiment a variable inductance and having a control circuit which operates the switches of the converter under zero voltage switching conditions and under continuous conduction mode by maintaining the quality factor of the resonant circuit generally equal to the DC conversion ratio.

Abstract: In a capacitively coupled DC-to-DC converter employing a pair of switching elements alternately rendered conductive, instabilities arising from current mode control are compensated for by detecting and controlling the amount of charge transferred by each switching element to a respective output capacitor associated therewith rather than the conduction period of each switching element. Converter instabilities arising from switching element duty cycles in excess of 50% are compensated for by integrating the sensed inductor current which represents the average inductor output current rather than its instantaneous value. An integrating network is discharged to 0 at the end of each cycle in resetting the sensed inductor current to 0 to prevent converter runaway when the switching element duty cycle exceeds 50%. This invention is applicable for all types of DC converters operating with a duty cycle greater than 50%.

Abstract: In power circuit designs, it is sometimes necessary to connect two or more semiconductor power switches in parallel and to simultaneously operate both so that current levels in excess of the rated current handling capability of one of the devices can be conducted. Such operation, however, encounters the problem of current sharing which results from variations in the characteristics of the parallel-connected devices. The method of the present invention obviates the difficulties encountered with current sharing by operating N parallel-connected semiconductor devices one at a time in sequential fashion so that each device conducts an average current equal to the desired average output current divided by N.