Showing papers by "J.A. Cobos published in 1992"

The determination of the boundaries between continuous and discontinuous conduction modes in PWM DC-to-DC converters used as power factor preregulators

Abstract: The determination of the boundaries between both modes of conduction (continuous and discontinuous) in PWM DC-to-DC switching power converters used as power factor preregulators (PFP) is presented in this paper. When a DC-to-DC switching power converter works as a power factor preregulator, its operating point is constantly changing due to the fact that both the DC voltage conversion ratio and the load "seen" by the power converter are constantly changing in each half-sinusoid of the line voltage (input voltage of the converter). In these conditions, the conduction mode cannot be directly determined. In this paper, the boundaries between both conduction modes in each angle of the half-sinusoidal input voltage have been determined. The conditions to always operate in continuous or in discontinuous conduction modes have been determined as well. Finally, these results have been verified by simulations and experimental results. >

Study of the applicability of self-driven synchronous rectification to resonant topologies

Abstract: Synchronous rectification techniques applied to high-frequency resonant topologies are studied. The on-resistance reduction of the MOSFET synchronous rectifier produces an increase of the parasitic capacitances. A selection of the resonant topologies where these capacitances are absorbed by the resonant tank, allowing self-driving of the synchronous rectifier, is presented. High efficiency has been obtained in a low-output-voltage (5 V and 3.3 V) forward ZVS-MRC with resonant synchronous rectification. Layout effects appeared to be very important at high switching frequencies. Even better results are expected in a hybrid prototype using specific low gate resistance MOSFETs as synchronous rectifiers. >

Analysis of the zero-current-switched quasiresonant converters used as power factor preregulators

Abstract: The use of zero-current-switched quasi-resonant converters (ZCS-QRCs) as power factor preregulators (PFPs) is studied The study is applicable to boost, buck-boost, flyback, SEPIC, and Cuk topologies The main conclusion is that the switching frequency variation range using a half-wave resonant switch is lower than that using a full-wave resonant switch if the load connected to the output is almost constant Moreover, using topologies with a transformer (flyback, SEPIC or Cuk), this variation range can be minimized choosing an adequate value of the normalized switching frequency at the peak of the sinusoidal input voltage However this range increases greatly when the load changes in the same manner In this case, a reduced switching frequency variation range is obtained using a full-wave switch However, this type of resonant switch decreases the efficiency because it handles reactive energy, and then a trade-off between switching frequency variation range and efficiency must be considered >

Review of suitable topologies for on-board DC/DC converters in distributed power architectures for telecom applications

Abstract: Distributed power systems architectures have been proposed as an optimal choice for many telecommunication applications. In these architectures, the DC/DC conversion stage is an on-board converter with very hard specifications in terms of efficiency and size. Some of the most usual specifications for telecom on-board DC/DC converters are considered, and the most suitable topologies are reviewed for each case. Pulse width modulated (PWM) quasi- and multiresonant topologies are taken into consideration and comparative analysis is performed from the point of view of size, efficiency, reliability and EMC behavior. >