Rafael Diez

Synthesized High-Frequency Thyristor for Dielectric Barrier Discharge Excimer Lamps

Dielectric barrier discharge (DBD) lamps, being capacitive loads, must be associated with bidirectional current sources for an appropriate control of the transferred power. Pulsed current source supplies, which are known to offer very interesting performances, require specific power switches that are able to manage bidirectional voltage and unidirectional current at much higher frequencies (several hundreds of kilohertz) than commercial thyristors. This paper proposes the detailed design of such a high-speed synthesized thyristor, using discrete components: a MOSFET in series with a high-voltage (HV) diode and a logic circuit that controls its gate. This switch is associated with an optimized self-powered driver, which is a very efficient solution to handle the perturbations associated with the HV and high-frequency operation. Experimental application of this device for DBD excimer lamp supply is proposed.

Current-Mode Power Converter for Radiation Control in DBD Excimer Lamps

A pulsed current-mode converter specifically designed for the supply of dielectric barrier discharge excimer lamps is proposed in this paper. The power supply structure is defined on the basis of causality criteria that are justified by the structure of the lamp model. The converter operation is studied, and its design criteria are established using state-plane analysis. This converter, operating in discontinuous conduction mode, controls directly both the amplitude and the duration of the emitted ultraviolet (UV) pulses. Experimentally, the UV radiation is demonstrated to be proportional to the current injected into the gas, and the degrees of freedom offered by the control of the supply are shown to be very efficient for the active control of the UV power.

Pulsed Current-Mode Supply of Dielectric Barrier Discharge Excilamps for the Control of the Radiated Ultraviolet Power

UV excimer lamps are efficient narrowband sources of UV radiation with applications in various domains. The issue of controlling the UV emission by means of the power supply associated with such lamps favors pulsed current-controlled generators. After having established the previous statements, we propose a dedicated power converter topology which implements the needed performances. The analysis of the degrees of freedom of this structure shows the capability of this pulsed supply to realize the control of both the pulses current energy and of the mean power transferred to the lamp. Actual experimental realizations and measurement are presented and the feasibility and the performances of the proposed solutions are established.

Current mode converter for dielectric barrier discharge lamp

This paper presents a novel concept of supplying a dielectric barrier discharge (DBD) lamp. An electrical model of the lamp is used in a circuit simulator to study the interactions between the converter and the load, which presents a capacitive nature. The current mode supply is chosen instead of the classical voltage mode, in order to respect the causality considerations concerning these interactions. The converter is designed as a unidirectional current source in series with an H-bridge that inverts the current direction in the lamp each half cycle. Two different structures are presented to compose the unidirectional current source: a Boost based converter and a Buck-Boost based converter. Both converters are analyzed using the state plane and implemented, obtaining measurements that comply with the current mode concept. The presented structures allow the control of the current duration and amplitude, thus, the operating point in the discharge. This concept is the basis for the studies of correlation between the gas current and the UV emission.

Design of a current converter for the study of the UV emission in DBD excilamps

This paper presents the design of a current converter to supply a DBD exciplex lamp. The structure is implemented, based on a Boost converter. An analysis in the state plane is used, to determine the stability of the converter and the values of current and voltage during the discharge phase. An electrical model of the lamp is used to simulate the non measurable variables: the gas current and the gas conductance. Finally, the relationship between the gas current and the UV emission is presented.

Square-Shape Current-Mode Supply for Parametric Control of the DBD Excilamp Power

With the aim of providing a power supply for the study of dielectric barrier discharge (DBD) excimer lamps (excilamps), a current-mode converter that allows for an accurate adjustment of the electrical power injected into one of those lamps is designed and implemented. Starting from the electrical model of the DBD lamps, the convenience of using a current-mode supply to control the lamp power is demonstrated. With the proposed converter, the current supplied to the lamp has a trapezoidal almost-square shape controlled by means of three parameters, namely, amplitude, duty cycle, and frequency, which provides full control of the lamp electrical power. Implementation is made considering a step-up transformer interfacing the high-voltage lamp with the converter. Experiments demonstrate the operating principle of this converter, including ultraviolet power measurements for a DBD XeCl excilamp. The capabilities of the converter are used to analyze the lamp behavior under different combinations of these three parameters, illustrating its capabilities for finding the optimal operating point of a DBD reactor.

Innovative power supply concepts for DBD excilamps

Excimer and exciplex UV/VUV sources excited by Dielectric Barrier Discharges represent a promising technology for industrial applications where powerful and efficient UV sources are needed. According to previous work, the most suited power supply waveform for coaxial DBD Excilamps is a unipolar pulsed voltage excitation of some kilovolts at some hundred of kilohertz with a duty cycle around one percent. We present here new concepts for energy supplying of coaxial DBDs, based on the direct control of the current in the lamps. These concepts have been tested by means of simulation models developed in our department and the time evolution of the UV radiation is presented for various considered current waveforms. Based on these results, a power supply topology has been designed for an efficient power transfer to the Excilamp. It is based on a converter which controls the current flowing through the DBD. The results concerning the coupling of this converter with a DBD load are commented.

DCM-Operated Series-Resonant Inverter for the Supply of DBD Excimer Lamps

This paper presents the study of a series-resonant inverter for the supply of a dielectric barrier discharge excimer lamp. Causal analysis, based on the fundamental properties of the load, is used to detail the reasoning which has led to this topology. In order to effectively control the lamp power, the operating mode of this converter combines discontinuous current mode and soft commutation (zero-current switching), obtaining low electromagnetic emissions and reduced switching losses as well. The model of the lamp is briefly presented, and it allows a simple state plane analysis to calculate all the electric variables involved in the converter and, consequently, to select the components of the supply. The mathematical relationships obtained from this process, for injected power control by means of the available degrees of freedom, are validated with simulations and experimental results.

Designing the high voltage transformer of power supplies for DBD: Windings arrangment to reduce the parasitic capacitive effects

In Dielectric Barrier Discharges (DBDs), the control of the power transfer, from the low-voltage static converter to the high voltage DBD, is strongly affected by the parasitic capacitive effects of the step-up transformer. Minimizing these capacitances is of major importance and this paper aims to establish and validate analytical expressions in order to predict the values of the parasitic capacitances of high ratio, step-up transformers, according to different windings arrangements using cylindrical conductors. Afterward, experimental validations are performed on three transformers which have been realized according to same specifications, in order to show the accuracy of the method and to understand the influence the winding arrangements on the capacitive parasitic effects.

Impact of the transformer in the current mode supply of dielectric barrier discharge excimer lamps

This paper presents an analysis of the consequences of using a step-up transformer in the supply of a dielectric barrier discharge (DBD) excimer lamp. A simplified transformer model is used to analyze the effects of the different parasitic elements in the operation of a current mode power supply. Mathematical expressions are found for each element and experimental validation is performed. The design of the transformer is developed on the basis of the lamp specifications and two transformer configurations are tested experimentally, analyzing the effect of the parasitic elements and evidencing the influence of grounding a lamp terminal.