Showing papers by "Dragan Maksimovic published in 1998"

Nonlinear-carrier control for high-power-factor rectifiers based on up-down switching converters

Abstract: In this paper, nonlinear-carrier (NLC) control is proposed for high-power-factor rectifiers based on flyback, Cuk, Sepic, and other up-down power converters operated in the continuous conduction mode (CCM). In the NLC controller, the switch duty ratio is determined by comparing a signal proportional to the integral of the switch current with a periodic nonlinear-carrier waveform. The shape of the NLC waveform is determined so that the resulting input-line current follows the input-line voltage, as required for unity power factor rectification. A simple exponential carrier waveform generator is described. Using the NLC controller, input-line voltage sensing, error amplifier in the current-shaping loop, and multiplier/divider circuitry in the voltage feedback loop are eliminated. The simple high-performance controller is well suited for integrated-circuit implementation, Results of experimental verification on a 150 W flyback rectifier are presented.

A multiple-winding magnetics model having directly measurable parameters

Abstract: A general model of the multiple-winding transformer and coupled inductor is presented, in which all parameters can be directly measured. The approach is suitable for all winding geometries, and simplifying approximations can be easily made. This model can be applied in the determination of cross-regulation, current ripple and small-signal dynamics of multiple-output DC-DC power converters. An experimental four-winding flyback transformer example is investigated. Observed leakage inductance parameter measurements are interpreted physically, and are related to observed flyback converter waveforms. It is also shown that the model correctly predicts small-signal dynamics.

DC-DC converter with fast transient response and high efficiency for low-voltage microprocessor loads

Abstract: The paper describes a DC-DC power converter for use with low voltage microprocessor loads. The control method is a hysteretic current-mode control in the continuous conduction mode which has fast transient response. At light loads, the power converter operates in the discontinuous conduction mode using a peak current control method which causes the switching frequency to be proportional to load current, thus maintaining high efficiency in a very wide range of loads. The control method implementation, transient response and output inductor design equations, and equations for designing an input filter to reduce input current di/dt are provided. An inductor current estimator which provides higher efficiency, good transient response, and current limiting, is presented. Experimental results for a 5.0 V input, 3.1 V output, 13 A DC-DC converter are included to verify the theoretical information.

Modeling of cross-regulation in converters containing coupled inductors

Abstract: A general model of the multiple-winding coupled inductor is described, in which all parameters can be directly measured. This model is employed in a tutorial explanation of the mechanisms by which leakage inductances and effective turns ratios affect cross regulation and discontinuous conduction mode boundaries in a multiple-output converter. Three basic approaches to coupled-inductor design are compared: near-ideal coupling, practical moderate coupling, and the zero-ripple approach. Near-ideal coupling results in good cross-regulation even when some outputs become discontinuous; however, realization of near-ideal coupling may be difficult in practice, and the resulting circulating currents can also lead to increased output voltage ripples and reduced efficiency. The best cross regulation can be obtained via the zero-ripple approach with relatively loose coupling in applications where there is at least one output whose load current variations are relatively small so that all windings can always operate in the continuous conduction mode. The conclusions are supported by experimental results.

Power factor correctors based on coupled-inductor Sepic and Cuk converters with nonlinear-carrier control

Abstract: This paper presents the design of high performance power factor correctors based on coupled-inductor Sepic and Cuk power converters operating in the continuous conduction mode. All inductive components are realized on the same magnetic core and designed so that levels of switching-frequency ripples and conducted EMI are greatly reduced. Input-current shaping and output voltage regulation are accomplished using the nonlinear-carrier control technique. A Spice-compatible large-signal averaged model is introduced to facilitate computer-aided design verification. The design and the models are validated by experimental results on two power factor correctors based on the coupled-inductor Sepic and Cuk power converters.

Automated small-signal analysis of switching converters using a general-purpose time-domain simulator

Abstract: The paper describes a method for automated small-signal frequency response analysis based on transient response obtained using a general-purpose simulation tool such as Spice. The method is based on using the simulation tool to evaluate the converter impulse response. The main advantage of the proposed method as a design verification tool is that frequency responses can be generated efficiently for any converter configuration and any model complexity supported by the general-purpose simulator. Application examples are included to demonstrate very good correlation between the generated responses and experimental data, and to compare the results with predictions of approximate analytical methods.