Gert W. Bruning

Analysis of the self-oscillating series resonant inverter for electronic ballasts

In this paper, we examined the self-oscillating series resonant inverter for electronic ballast applications from a system point of view. By considering the discharge lamp as a linear resistor in steady state, we derived a time-domain closed form expression of the circuit state variables. Importantly, we observed that the self-oscillating series resonant inverter with lamp loads can be naturally modeled as a relay system. Based on this formulation, the self-oscillating frequencies of the inverter for variable lamp impedance conditions are found via the Tsypkins locus. The stability of the self-oscillating frequencies is determined in a sampled-data system framework.

Voltage-fed half-bridge resonant converter for multiple lamp independent operation

In this paper, we explore the voltage-fed half-bridge LLC resonant converter for multiple lamp parallel independent operation (ILO). Based on the observation of almost invariant voltage gain relation with the resonant tank input impedance phase angle for different number of lamps, we propose the so-called phase-shift based control method. With this method, multiple lamp ILO is achieved under voltage-fed half-bridge LLC resonant converter with zero-voltage-switching (ZVS). Experimental results are presented for instant start 4-lamp TL70 F32T8.

A New High-Voltage Oscillator

A current-fed parallel resonant oscillator switched in push-pull mode for providing ac power at high frequency is presented. The primary advantage of this circuit over existing high-voltage oscillators lies in its built-in voltage-gain dependence on the load. Furthermore, the duty-cycle of the switching elements is inherently limited to less than 50 percent. This avoids destructive overlap periods of the on- or off-time of these switches at all times. As a result a wide range of loads can be accommodated.

A high efficiency magnetic component with superior caloric performance

A magnetic component structure is described that has both low profile and the ability to achieve very high power and energy densities. A key feature towards reaching both of these objectives is the incorporation of a foil winding with a high packing density and a unique shape factor, which enhances thermal and electromagnetic performances simultaneously. Although implementation of foil windings is common practice in magnetic component design, vertically wound foils to achieve low profile is not. Three prototype inductors are compared to a conventional litz-wound E-core inductor. Power dissipation and temperatures are measured in several different experimental procedures. At 140 kHz a power density of 1.8 kVA/in/sup 3/ was achieved for a measured efficiency of 99.5% and a steady-state hot spot temperature rise above the ambient of only 55/spl deg/C.