Thomas Duerbaum

Comparison of methods for the analysis of the parallel resonant converter with capacitive output filter

Several different approaches for the investigation of the steady-state properties of resonant converters have been published to date. In addition to solving the occurring equations in the time domain, which turns out to be quite cumbersome, the designer can make use of approximate approaches in the frequency domain. Two of these methods are compared to the exact solution with regard to their accuracy and mathematical complexity within this paper for the parallel loaded resonant LC converter with capacitive output filter. Some practical aspects are discussed by means of measured voltage conversion ratios.

Characterization of a modified LISN for effective separated measurements of common mode and differential mode EMI noise

The compliance with standards calls for proper designed EMI filters. EMI typically comprises common mode (cm) and differential mode (dm) noise. A systematic optimization of EMI filters requires the knowledge of the contribution and distribution of these two noise sources. The paper discusses different methods that allow the independent measurement of cm and dm noise. One suitable method described in detail integrates the separation set-up into the Line Impedance Stabilization Network (LISN). However, a correct interpretation of the measured results requires a characterization of the unavoidable modal conversion of the complete set-up - i.e. the measured level at the dm output in case of pure cm excitation and vice versa. As shown in this paper, the implementation of a standard LISN introduces a high amount of imperfections causing the undesired modal conversion. Thus, for the first time, this paper describes the characterization of the whole set-up including the LISN.

Discrete modeling of resonant converters — Steady state and small signal description

Discrete modeling seems to be a fast and accurate method for describing resonant switch mode power converters. This paper applies discrete modeling onto resonant converters and shows it exemplarily for the series resonant converter. It shows how to calculate a nonlinear large signal model from which the steady state can be derived, as well as small signal transfer functions as it is the control-to-output transfer function, the audio susceptibility, and the output impedance. Furthermore, different possibilities of how to obtain these three transfer functions are shown and discussed. An excellent agreement between the different calculation methods shows the accuracy of this modeling technique. A great emphasis of this paper is placed on the determination of small signal transfer functions of resonant converters since this has still been an open issue so far.

Analysis and design of a partial-multi-resonant LLC converter

In this paper a resonant converter is shown, which is based on the series resonant parallel loaded LLC converter. Limiting the voltage across the resonant capacitance with clamping diodes to the input voltage range as shown here, has several advantages like excellent zero voltage switching performance.

ZVS investigation of llc converters based on FHA assumptions

While resonant converters have been gaining much attention within the recent years, their exact mathematical description is rather complicated. Thus, simplified calculation methods are very attractive, e.g. the First Harmonic Approximation (FHA). Although the steady state solution of these simplified methods is usually quite acceptable and close to the exact solution, the prediction of the ZVS characteristic is either neglected or treated to simple. The ZVS characteristic is typically directly related to the voltage transfer function resulting in a too optimistic estimation of the operation range obtaining ZVS. Therefore, this paper focuses on a more accurate investigation of the resonant LLC converters ZVS behavior and proposes two approximation methods, which are also based on simplified FHA assumptions allowing a fast estimation of different converter designs.

Automatic measurement of the reverse recovery behavior of ultra-fast diodes

Often data sheets provide only poor information about the recovery behavior of ultra-fast diodes. On the other hand, existing diode models do not predict the real characteristic for all diodes. Nevertheless, due to its importance, this behavior needs to be known and therefore measured. For this purpose, a fully automated measurement set-up for determining the reverse recovery characteristic of ultra-fast diodes in an accurate manner was designed and is described here. All the data obtained is immediately transferred into MATLAB and therefore available for further calculation, model building and model validation. Since the whole set-up is automated, a complete field of variations in the reverse voltage, the forward current, the temperature, and the di/dt can be easily applied to the tested diode. Hence, a lot of information can be obtained effortlessly. This uncomplicated methodology makes it readily available for circuit designers, allowing them to predict the contribution of the reverse recovery of rectifiers to the total losses more accurately. In addition, a real comparison of different diodes at many operation points is made possible.

The resonant LLC vs. LCC converter - comparing two optimized prototypes

Due to the increasingly demand for highly efficient, cost-effective and low-profile applications, resonant converter topologies are massively gaining in importance. With the LCC and LLC converter, the two most promising topologies of this converter class are presented and compared within this paper. Based on their individual configuration, both converters are analyzed in the time domain revealing the first differences and similarities. Moreover, both converter topologies are optimized with respect to a low-profile notebook adapter specification for 100 W. The main focus is placed on the magnetic design of both transformers. Finally, two prototypes using completely identical layouts are developed and measurement results are discussed concerning best operation point and overall efficiency.

Sampled-data modeling applied to output impedance reveals missing term in state-space averaging model

The investigation of the stability of larger power systems requires knowledge about output impedances of switch mode power supplies (SMPSs). Methods for the prediction of this quantity of a SMPS comprise state-space averaging and sampleddata modeling. However, results obtained from both methods exhibit large differences. Furthermore, sampled-data modeling itself yields completely different results for different sampling points. Negative as well as positive incremental impedances may occur. Nevertheless, considerations of the steady-state in time domain prove the existence of these strongly different results, as discussed in this paper. In addition to that, it will be shown that only small additional effort is necessary to simulate the converter behavior with exact averaged quantities. This leads directly to an improvement of the state-space average model by means of adding an operating point dependent resistor.

Characterisation of an effective EMI noise separation including a standard LISN

The compliance with standards calls for proper designed EMI filters. EMI typically comprises common mode (cm) and differential mode (dm) noise. A systematic optimization of EMI filters requires the knowledge of the contribution and distribution of these two noise sources. The paper discusses different methods that allow the independent measurement of cm and dm noise. One suitable method described in detail integrates the separation set-up into the Line Impedance Stabilization Network (LISN). However, a correct interpretation of the measured results requires a characterization of the unavoidable crosstalk of the complete set-up - i.e. the measured level at the dm output in case of pure cm excitation and vice versa. As shown in this paper, the implementation of a standard LISN introduces the highest amount of imperfections causing the undesired crosstalk. Thus, for the first time, this paper describes the characterization of the whole set-up including the LISN.

Analysis and design of a resonant LCC converter for low-profile applications

In addition to high efficiency of switch mode power supplies, miniaturization of converters is an increasingly important aspect. In order to meet safety regulations as well as the design goal of flatness, complicated integrated magnetics are proposed in literature. Unfortunately, their design is difficult and the costs of these components are rather high. This paper focuses on the resonant LCC converter with capacitive output filter, which is a promising topology with respect to low-profile designs. The transformer necessary for mains isolation is realized on a ring core, thus regulation requirements are combined with a low-cost magnetic component. The exact analysis of the LCC converter in the time domain is presented and the solutions of the four important modes of the converter are derived. A prototype was designed in order to demonstrate the feasibility of the proposed approach with an application scenario typical for notebook adapters.