Sounil Bhosle

OLED Electrical Equivalent Device for Driver Topology Design

In this paper, a hardware equivalent of an organic light-emitting diode (OLED) was designed and investigated. This substitution OLED device is based on a circuit-equivalent OLED model and can be used to design and test OLED dedicated drivers. Indeed, OLEDs are available on the market, but they are still very expensive and hard to obtain. Compared to a real OLED, the substitution device is cheap and robust and can be easily duplicated. Moreover, a photodetector is not required to measure the light output waveform. This can be simply done by measuring a voltage across a resistance. This model can be used, for instance, to simulate a large OLED panel made of several associated single OLEDs for various series/parallel connection strategies. It can also be used to simulate aging phenomena by changing the values of some of its components. This might be useful for the definition of strategies to compensate aging effects like luminous flux depreciation. Another advantage of such a device is its use for power supply tests as it could serve as a substitution load, at maximum deviation from standard OLED electrical characteristics. We discuss the theoretical model that was used as a basis for developing the device. The accuracy of the model was then evaluated, particularly in pulsewidth-modulation dimming conditions. Then, the hardware equivalent device was compared to a real OLED. Finally, an example of the potential use of this substitution device is given: It was successfully used to investigate the “overdrive” technique in order to increase OLED light output rise time. This technique improves the light output rise time by a factor of over 4.

Characterization of Acoustic Resonance in a High-Pressure Sodium Lamp

In the last decades, the high-pressure sodium (HPS) lamp has been supplied in high frequency in order to increase the efficacy of the lamp/ballast system. However, at some given frequencies, standing acoustic waves, namely, acoustic resonance (AR), might develop in the burner and might cause lamp luminous fluctuation, extinction, and destruction in the most serious case. As we seek for a control method to detect and avoid the lamp AR, some main characteristics of ARs in a 150-W HPS lamp are presented in this paper. The first one is the characteristic of the lamp AR threshold power, and the second one is the differences between the forward and backward frequency scanning effects during lamp open-loop operation. Third, the lamp AR behavior in closed-loop operation with an LCC half-bridge inverter will be presented, and it leads to a new point of view and a change in the choice of the AR detection method. These characteristics allow us to further understand AR and to better control the lamp.

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.

Electrical modeling of an homogeneous dielectric barrier discharge (DBD)

Dielectric barrier discharge (DBD) excimer or exciplex lamps are known as efficient UV and VUV sources but their power supply operates at a high voltage (some kV) and at a frequency of some tens of kHz. Consequently, for industrial applications, DBD lamps need specific power supplies, designed for one lamp geometry and gas filling. The aim of this work is to provide an improved electrical model for a homogeneous DBD which can provide relevant electrical parameters such as gas voltage drop, total current, sheath voltage and current, surface charge deposited on the dielectric surfaces but can allow for fast simulation times.

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.

Acoustic resonances in HID lamps: model and measurement

A finite element model including plasma simulation is used to calculate the amplitude of acoustic resonances in HID lamps in a 2D axisymmetric geometry. Simulation results are presented for different operation parameters and are compared with experimental data.

Implementation of an efficiency indicator in an electrical modeling of a Dielectric Barrier Discharge Lamp

Dielectric barrier discharge (DBD) excimer or exciplex lamps are known as efficient UV and VUV sources but their power supply operates at a high voltage (some kV) and at a frequency of some tens of kHz. Consequently, for industrial applications, DBD lamps need specific power supplies, designed for one lamp geometry and gas filling. We have proposed in [Bhosle, S et al., 2004] and [Bhosle, S et al., 2005] an electrical model of a DBD which can be implemented in an electrical simulation software and can thus be used as virtual load for innovative DBD power supply design. The aim of that paper is to describe the mechanisms involved in the development of an homogeneous DBD and their transcription to an electrical equivalent circuit where the UV flux of the discharge can be estimated

Finite element estimation of acoustical response functions in HID lamps

High intensity discharge lamps can experience flickering and even destruction when operated at high frequency alternating current. The cause of these problems has been identified as acoustic resonances inside the lamps arc tube. Here, a finite element approach for the calculation of the acoustic response function is described. The developed model does not include the plasma dynamics.

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.

Circuit-Based Model for a Dielectric Barrier Discharge Lamp Using the Finite Volume Method

A physically based circuit model for the dielectric barrier discharge (DBD) lamp using the finite-volume method is developed in this paper. This model provides the electrical and optical characteristics of the lamp. Using this model, the influence of the electrical excitation on the lamp efficiency can be investigated. A model order-reduction technique which preserves the circuit-based formulation and provides sufficient accuracy has been developed. The reduced-order circuit-based model facilitates the design of a DBD lamp driver with short simulation times.