Showing papers by "Robert Louis Steigerwald published in 1996"

Resonant converter with wide load range

Abstract: Low-power auxiliary circuitry is added to a resonant converter for providing high efficiency operation, low EMI, and tight output voltage control over a wide load range. There is an auxiliary circuit corresponding to each half-bridge connection of main switching devices, each auxiliary circuit including a half-bridge connection of auxiliary switching devices with the junction therebetween coupled to the junction between the main switching devices of the corresponding half-bridge. Under heavy load conditions, sufficient energy is stored in the main resonant inductor to commutate the junctions joining the main switching devices in the resonant converter, resulting in zero-voltage switching for the main switching devices. Under light load conditions, a phase shift is introduced between the corresponding main and auxiliary switching devices, and the auxiliary resonant inductor currents are increased to a level sufficient for the sum of the main resonant inductor current and the corresponding auxiliary resonant inductor current to provide zero-voltage switching for all the bridge switching devices.

Auxiliary series resonant converter: a new converter for high-voltage, high-power applications

Abstract: The power converter presented in this paper has been designed to meet high-quality power requirements in high-voltage, high-power applications such as X-ray imaging, traveling wave tube RF generation, etc. The new power converter is based on a series resonant power converter (SRC) which is modified by adding low power auxiliary circuitry. The so obtained auxiliary SRC (ASRC) maintains zero-voltage switching (ZVS) for both main and auxiliary devices over the entire operating range. The ASRC can operate and regulate voltage even at no load conditions. The additional reactive energy used to maintain soft switching and voltage regulation at light loads is controllable independently of power converter load. This contributes to higher efficiency, especially at heavy loads. The ASRC control is identical to that of a standard SRC, so fast and robust transient response can be obtained with relatively simple controller structure. The paper also presents power converter analysis and design, and experimental results from a 100 kW, 150 kV prototype.

Square-wave converters with soft voltage transitions for ac power distribution systems

Abstract: A converter for an ac power distribution system provides a square-wave voltage of low output impedance to an ac power distribution bus for driving a plurality of loads, each load including a rectifier and an input filter capacitor. Slew-rate limiting capacitors are employed to limit the rate of change of voltage on the ac distribution bus, thereby substantially reducing or eliminating conducted and radiated interference from the power distribution system due to high-frequency components of current which would otherwise flow in parasitic capacitances. In addition, zero-voltage switching is employed to achieve highly efficient converter operation. As other advantages, this converter scheme allows for simplification of converters at the load end of the power distribution system (e.g., to simple rectifiers with post regulators), while producing lower ac line currents, lower current harmonics and higher power factors than those of a sine-wave generation system.

High-frequency switching circuits operable in a natural zero-voltage switching mode

Abstract: A dc-to-dc power converter, comprising a transformer, a single primary-side power switching device and a parallel combination of a diode and a capacitance, is controlled to operate in a "natural" zero-voltage switching mode such that the power switching device is switched with zero-voltage thereacross. Due to the simplicity of the circuit, i.e., very few components, and its high-frequency capability, it can be implemented using high-density packaging techniques. Such a converter is useful in ultra-high-density point-of-load dc-to-dc converters for distributed power systems.

High-frequency, high-efficiency converter with recirculating energy control for high-density power conversion

Abstract: A front-end converter processes only a fraction (e.g., about 10%) of the power delivered by an efficient output (i.e., the main) converter in order to control the output voltage thereof. Because only a fraction of the delivered power is processed, the losses associated with the front-end converter are a very small fraction of the total delivered power, leading to very high overall efficiencies. The input power to the front-end converter is provided from the output of the main converter; this reduced power is thus circulated within the converter. Regulation of the output voltage by controlling the dc voltage relieves the regulating function from the main converter, allowing the main converter to be selected strictly on the basis of efficiency and small size. The result is an overall efficient, compact dc-to-dc converter with minimal output filter requirements and protection against output short circuits. Additionally, the converter bandwidth is determined by the bandwidth of the low-power front-end converter which can have a higher bandwidth than a full-rated converter. Therefore, a significantly higher bandwidth can be achieved as compared with presently available converters, advantageously resulting in a reduced output filter size and faster speed of response.

Diagnostic circuit and method for predicting fluorescent lamp failure by monitoring filament currents

Abstract: A diagnostic circuit monitors filament currents in hot cathode fluorescent lamps for detecting when the filament erodes to the point of breaking. When such a filament failure is detected, information is processed and a request is sent to replace the lamp before it actually fails. The diagnostic circuit is low power and low voltage and is electrically isolated from the high-voltage end of the lamp. Additionally, a simple circuit to regulate rms value of filament voltage without having to compute or otherwise measure the actual rms value is provided.

A multi-function filament-heater power supply for an electronic ballast for long-life, dimmable lamps

Abstract: A filament-heater power supply includes a combination forward and flyback power converter for supplying electronically variable, isolated voltages to dimmable discharge lamp filaments while supplying a fixed dc output voltage to a ballast control circuit. Hence, only a single ballast power supply is needed. The control circuit controls the level of filament voltage to operate the lamp filaments at an optimum temperature, even during dimming operation, thereby substantially extending lamp life. The filament-heater power supply provides a high degree of isolation among filament voltages while regulating and tracking the voltage across each filament. The filament-heater power supply can preheat the filaments to aid lamp starting, thereby extending the useful life of the lamp, and is also structured to sense when a lamp is not present in a fixture so that high voltage starting pulses are not applied to the terminals of an empty fixture.

Elimination of striations in fluorescent lamps driven by high-frequency ballasts

Abstract: A ballast system for at least one dimmable fluorescent lamp includes a ballast inverter for driving the fluorescent lamp to provide light output and a parallel impedance for coupling across the fluorescent lamp for providing an alternative path for diverting sufficient dc current to avoid developing striated light ouput as the light output is dimmed. The parallel impedance may be a resistor connected in series with a diode. For multiple lamp systems, the parallel impedance may be connected across one or more of the lamps.

Control and protection of dimmable electronic fluorescent lamp ballast with wide input voltage range and wide dimming range

Abstract: A ballast system for at least one dimmable fluorescent lamp includes a resonant switching inverter and a controller which controls the inverter to operate above resonance during starting and normal running operation. After a start delay timer alloys time for the lamp filaments to heat up, the controller provides control signals to a gate driver to drive the switching devices of the switching inverter initially at a relatively high frequency and then reduces the frequency until a sufficiently high voltage is reached to start the lamp. Once the lamp is started, the inverter is operated in its normal feedback mode. The ballast system further includes an overvoltage shutdown mechanism. During lamp starting, if either the output of the start delay timer is high or the output voltage is greater than a first overvoltage shutdown threshold, then an overvoltage shutdown timer is activated to shut down operation of the inverter for a predetermined overvoltage shutdown period. After the lamp has started, a second overvoltage shutdown threshold is activated which is lower than the first overvoltage threshold for avoiding operation of the inverter below resonance. Both the frequency and duty cycle of the output voltage from the switching inverter are variable to achieve a wide dimming range over a relatively narrow frequency range.

Very low leakage inductance, single-laminate transformer

Abstract: A transformer having a very low, predetermined leakage inductance includes an elongate dielectric laminate having two surfaces. A primary winding having a pattern conformal to the configuration of the laminate is disposed on one surface and extends substantially the length of the laminate. The laminate has at least one secondary winding disposed on its other surface. The laminate is rolled with a dielectric layer about a cylinder, and the primary and secondary windings are patterned such that the primary and secondary windings comprise interleaved winding layers with the dielectric layer disposed between each of the winding layers. The rolled laminate, dielectric layer, and windings are contained within a cylindrical magnetic pot core. The result is a transformer having tightly interleaved primary and secondary windings and, therefore, a very low leakage inductance. In addition, the distance between adjacent primary and secondary turns is fixed by the thickness of the dielectric layer; hence, the leakage inductance is highly predictable.