P. Villegas

High-efficiency and wide-bandwidth performance obtainable from a two-input buck converter

A study of the two-input post-regulators is carried out in this paper. In these post-regulators, only a part of the total power undergoes a switching conversion process, whereas the remainder of the power comes up to the load directly, with no power conversion process. Due to this fact, very high efficiency is achieved. Moreover, the stress in the semiconductors and the filter size are both much lower than in standard post-regulators. Two-input post-regulators require two-output main converters. However, many converter topologies can be easily adapted to supply two-output voltages with no efficiency penalty. Two-input postregulators can be used in many power converters. Multiple-output DC-to-DC converters and AC-to-DC power factor correctors are two good examples.

A microcontroller-based emergency ballast for fluorescent lamps

This paper presents a new emergency ballast for fluorescent lamps. The fundamental block is the microcontroller-based control circuit, which performs the supervision and control function. High-frequency electronics techniques are proposed for the high power factor battery charger and the lamp driver, which provides high luminous efficacy. In this way, size and weight have been minimized for the whole system. With the introduction of the microcontroller, the system has the capability of testing itself, checking its functional state, and displaying internal faults. Thus, the reliability of the system is improved and, concurrently, maintenance cost is decreased.

Helpful hints to select a power-factor-correction solution for low- and medium-power single-phase power supplies

This work presents a review of power-factor-correction (PFC) circuits for low- and medium-power single-phase power supplies. The main idea is not just to show the state of the art of this topic but to select the most interesting topologies for each application depending on the power level, the input voltage range, and the output voltage. Since IEC 61000-3-2 regulations came into force, many new topologies have been presented trying to obtain a cost-effective solution to reduce the input current harmonic content. Each one of them has its application range due to the inherent characteristics of the topology. Obviously, not every converter is useful for the same application. This is especially perceptible in PFC circuits due to the large amount of different solutions. Hence, this paper tries to show the most appropriate topologies for each application, being the input power and the IEC 61000-3-2 Class some of the main parameters to select it. The scope of the paper is focused on single-phase power supplies belonging to IEC 61000-3-2 Class A and Class D with an input power level below 4 kW.

Dynamic limits of a power-factor preregulator

Power-factor correction has been one of the hottest topics during the last few years and, hence, many new circuits have appeared. In general, it is assumed that preregulators based on multiplier circuits have poor dynamics and, then, a second stage is needed to improve the output voltage dynamic behavior. The other option is the use of single-stage topologies which have fast output voltage regulation although the input current waveform is not sinusoidal. This work presents an analysis of the dynamic behavior of a conventional power-factor preregulator. The objective is to find the limits of the dynamic characteristics of these circuits when the priority is to improve the output voltage regulation and not the total harmonic distortion or the power factor. A large-signal model is presented and the theoretical results are validated with a prototype.

Input current shaper based on the series connection of a voltage source and a loss-free resistor

A new input current shaper is proposed in this paper. The operating principle is based on the connection of a voltage source and a loss-free resistor (LFR) between the input rectifier and the bulk capacitor in a conventional switching mode power supply with no power-factor correction. Both the voltage source and the LFR are obtained as an additional output from the converters transformer. This additional output is a forward-type one with one extra inductor. With the final topology, a good tradeoff between capacitor voltage, recycling energy, and harmonic content can be established in order to comply with IEC 1000-3-2 specifications.

A new input current shaping technique using converters operating in continuous conduction mode

A new input current shaping technique has been proposed. Its operating principle is based on the connection of an additional DC output, obtained from the converters transformer, between the input rectifier and the bulk capacitor in a conventional switching-mode power supply with no power factor correction. This additional output is a forward-type one with one extra inductor, which provides an effective duty cycle modulated by the input current. Thus, the voltage-current characteristic of this output consists of a voltage source and a loss-free resistor, connected in such a way that they help the diodes of the line rectifier to conduct. The main difference with other input current waveshapers lies in the fact that the filter inductor of the additional output operates in continuous conduction mode. Thus, the current stress in the power transistor is minimized. With the final topology, a good trade-off between bulk capacitor voltage, re-cycling energy, power factor and harmonic content can be established in order to comply with the IEC 1000-3-2. Many aspects in the design and operation of this type of converter are analyzed in this paper.

Very efficient two-input DC-to-DC switching post-regulators

A study of the two-input post-regulators is carried out in this paper. In these post-regulators, only a part of the total power undergoes a switching conversion process, whereas the remainder of the power comes up to the load directly, with no power conversion process. Due to this fact, very high efficiency is achieved. Moreover, the stress in the semiconductors and the filter size are both much lower than in standard post-regulators. Two-input post-regulators require two-output main converters. However, many converter topologies can be easily adapted to supply two output voltages with no efficiency penalty. Two-input post-regulators can be used in many power converters. Multiple-output DC-to-DC converters and AC-to-DC power factor correctors are two good examples.

Improving dynamic response of power factor preregulators by using two-input high-efficient post-regulators

A new method to improve dynamic response of power factor preregulators (PFP) is developed in this paper. The method is based on the use of a very high efficiency post-regulator with two inputs instead of only one. This two-input post-regulator exhibits very high efficiency due to the fact that only a part of the total power undergoes a power conversion process. They need two-output PFPs at their inputs, which can easily be obtained in PFPs with transformers or with two PFPs working in parallel.

New active input current shapers to allow AC-to-DC converters with asymmetrically driven transformers to comply with the IEC-1000-3-2

Four new topologies of active input current shapers (AICSs) for converters with symmetrically driven transformers (such as half-bridge, full-bridge and push-pull) have been proposed. This paper analyzes the extension of the use of these new AICSs topologies to converters with asymmetrically driven transformers. Using some of these topologies, the size of AICS inductors can be reduced and even integrated in a single magnetic core. As in the case of other converters with AICS circuit, the new topologies allow line current harmonics to be reduced and thereby to comply with the IEC 1000-3-2 specifications, whilst maintaining all the features of standard DC-to-DC converters (e.g., fast transient response). Finally, the proposed topologies have been experimentally tested.

A new active input current shaper for converters with symmetrically driven transformer

This paper deals with the analysis of a new implementation of the proposed active input current shaper (AICS). This implementation allows us to use an AICS with DC-to-DC topologies in which the voltage across the transformer is a symmetrical waveform, e.g. half-bridge, push-pull or full-bridge converters. Using this implementation, the size of the AICS inductors can be reduced and even integrated in only one magnetic core. As in the case of other converters with AICS, the new implementation allows us to reduce the line current harmonics in order to comply with the IEC 1000-3-2 specifications, maintaining all the features of the standard DC-to-DC converters (e.g. fast transient response). Finally, four of the proposed topologies has been experimentally tested.