Buck converter small-signal models and dynamics: comparison ofquasi-resonant and pulsewidth modulated switches

The generalized canonical model obtained from extended state-space averaging is used as a design tool for the evaluation of the buck converter dynamics in different switching schemes. Designs are given at a specified constant conversion ratio and load for the pulse width modulated, zero current, zero voltage, and nonlinear resonant switch full- and half-wave converters. The small signal equivalent circuit model is discussed, and the feedback effects introduced by resonant switching on line and control transfer functions are evaluated. The small signal transfer functions of half-wave converters are heavily load-current dependent, and exhibit significant damping at light loads, which can result in two real poles in the converter response instead of a complex conjugate pair. This damping effect is evaluated over the entire normalized load current range for the linear and nonlinear zero-current switching converters. Simple approximate expressions are given for the real poles. Experimental verification of the half-wave analysis is presented, and the effects of converter efficiency on model accuracy are discussed     

Extension of state-space averaging to resonant switches and beyond

It is shown that the state-space averaging method can be extended by linear network theory from the domain of pulse-width-modulated converters to a much larger class, including resonant switches and current-programmed mode. The canonical model concept is also extended, and it is shown that the effect of resonant switching is to introduce a feedback block into the generalized canonical model. These results are applied to linear zero-current and zero-voltage resonant switches, a new class of nonlinear resonant-switch converters, and the current-programmed mode. Equivalent circuit models are developed for both full and half-wave operation, and experimental verification is presented     

Characterization and comparison of noise generation forquasi-resonant and pulsewidth-modulated converters

A buck converter with a given output filter is operated with pulse-width modulated and quasi-resonant switching schemes at the same nominal load and switching frequency. Electromagnetic interference generated by the natural switching action of the converter is examined by spectral analysis. Interference caused by excitation of parasitic elements is examined experimentally. Quasi-resonant converters are found to have a lower switching frequency harmonic bandwidth than the equivalent pulse-width modulated converter, even with switching frequency control. The most significant parasitic responses are the turn-on current and turn-off voltage of the catch diode and the gate current of the MOSFET. A significant decrease in radiated and conducted noise occurs when the gate drive voltage rise and fall times are increased, which is possible without loss of efficiency using quasi-resonant switching     

A nonlinear resonant switch

A resonant switch is introduced that uses linear tank elements. Zero-current switching is obtained even through the peak transistor voltage and current stresses can approach those of an equivalent ideal pulsewidth-modulated converter. Reduced switching loss without a substantial increase in conduction loss is therefore possible. An approximate analysis is outlined, and transistor peak-voltage and current stresses are shown to be much lower than those of linear resonant switch technologies. Single-transistor implementations of the buck, boost, and buck-boost nonlinear resonant switch converters are given. Results are presented which experimentally prove the validity of the nonlinear resonant switch concept, as well as that of the approximate analysis     

Small signal equivalent circuit modeling of resonant converters

A general analytical procedure is presented for the equivalent circuit modeling of resonant converters, using the series and parallel resonant converters as examples. The switched tank elements of a resonant converter are modeled by a lumped parameter equivalent circuit. The tank element circuit model consists, in general, of discrete energy states, but may be approximated by a low-frequency continuous time model. These equivalent circuit models completely characterize the terminal behavior of the converters and are solvable for any transfer function or impedance of interest. With the approximate model it is possible to predict the lumped parameter poles and zeros, and to quickly determine the relevant DC gains of the output impedance and the control to output transfer function. Closed-form solutions are given for the equivalent circuit models of both converter examples. Experimental verification is presented for the control-to-output transfer functions of both series and parallel resonant converters, and good agreement between theoretical prediction and experimental measurement is obtained     

Thermally Sprayed Coatings as Effective Tool Surfaces in Sheet Metal Forming Applications

Two approaches to produce wear-resistant effective surfaces for deep drawing tools by thermal arc wire spraying of hard materials are presented. Arc wire spraying is a very economic coating technique due to a high deposition rate. The coated surface is very rough compared to that of conventional sheet metal forming tools. In the first approach, the coated surface is smoothed in a subsequent CNC-based incremental roller burnishing process. In this process, the surface asperities on the surface are flattened, and the roughness is significantly reduced. In the second approach, the hard material coatings are not sprayed directly on the tool but on a negative mould. Afterward, the rough “as-sprayed” side of the coating is backfilled with a polymer. The bonded hard metal shell is removed from the negative mould and acts as the surface of the hybrid sheet metal forming tool. Sheet metal forming experiments using tools based on these two approaches demonstrate that they are suitable to form high-strength steels. Owing to a conventional body of steel or cast iron, the first approach is suitable for large batch sizes. The application of the second approach lies within the range of small up to medium batch size productions.     

On-Chip Characterization of Single-Event Transient Pulsewidths

A new on-chip single-event transient (SET) test structure has been developed to autonomously characterize the widths of random SET pulses. Simulation results show measurement granularity of 900 ps for a 1.5 mum technology and also indicate that the measurement granularity rapidly scales down with technology. Laser tests were used to demonstrate circuit operation on test chips fabricated using a 1.5 mum process. The experimental results indicate pulsewidths varying from about 900 ps to over 3 ns as the laser energy was increased     

Total dose effects on power-MOSFET switching converters

Power MOSFETs have important applications in space systems, particularly in dc/dc power conversion. Transistors used in the space environment are subject to the effects of exposure to the natural radiation environment in space. Among the effects of ionizing radiation are shifts in threshold voltage and reduction of carrier mobility. In this work, the total-ionizing-dose-induced degradation of two switching power converters is examined. The MOSFETs for two switching converters were irradiated with a ⁶⁰Co source and their performance was evaluated in buck and boost converters. The experimental results agree well with values obtained from SPICE simulations.     

Steady-state and large-signal design of current-programmed DC-DCconverters

A new method for steady-state design of current-programmed-mode (CPM) DC-DC converters is presented. The method uses a set of equations derived based on the relationships between line voltage, load current, control current, and the stabilizing artificial ramp. The set of normalized equations are verified by a fast large-signal simulation and experimental measurement. These equations are plotted on the converter DC output plane (a graph of output current versus output voltage) in which characteristic curves related to different artificial ramps and boundaries of different operating modes are indicated. A general design procedure is presented for a CPM converter with both input voltage and output resistive load varied. By this means, the design time can be significantly reduced, and systematic design trade-offs can be made to ensure correct converter operation over the desired range of line and load variation     

The non-hydrostatic response of polymer melts as a pressure medium in sheet metal forming

The polymer injection forming process is a recent invention for producing plastic?Cmetal hybrids. It is a combination of injection molding and sheet metal hydroforming process in which polymer melt serves as a pressure medium. This paper presents the experimental investigations on the non-Newtonian nature of thermoplastic melt as pressure medium. The objective of this work is to identify the presence of non-hydrostatic pressure distribution within the cavity and its influence on the final shape of the formed sheet metal component. Experiments are conducted with center-gated injection mold under varying processing conditions. The development of localized cavity pressure during the process is recorded and evaluated against the final shape of formed sheet metal. It has been observed that higher injection rate, higher injection temperature, and higher melt flow index of the processed polymer is necessary for the uniform pressure distribution and subsequently uniform forming of the sheet metal.