软开关双管正激电源设计方案

Quasi-ZVS Active Auxiliary Commutation Circuit

for Two Switches Forward Converter

J.E. Baggio, L. Schuch, H.L. Hey, H.A. Gründling, H. Pinheiro, J.R. Pinheiro Federal University of Santa Maria

CT / NUPEDEE / GEPOC

97105-900 - Santa Maria - RS - Brazil e-mail: josebaggio@, renes@ctlab.ufsm.br Abstract: This paper presents a family of

single-ended

process.

converters that adequately designed and commanded can The effects associated to these three factors are minimized

perform ZVS turn-off and turn-on with a value near to zero

by the use of zero voltage switching. However, some circuits

namely Quasi-ZVS (QZVS) at main switches. The auxiliary

do not operate with ZVS in all operation conditions. Even if

circuit presents low reactive energy and is composed of one

the voltage across the switch do not reaches zero, an

inductor, one diode and one switch, which operate with ZCS. To

improvement of the converter performance can be obtained,

demonstrate the feasibility of the proposed technique, it is

by using auxiliary circuits that reduce the voltage to values

applied to a two switches forward converter. It is not necessary

use of a third winding in the transformer neither auxiliary Voltage sources to achieve soft switching. The implementation is possible due to the use of an appropriate command, different than it is used conventionally in two switches forward near to zero. This is the basic principle of Quasi-ZVS (QZVS): to reduce the voltage across the switch to a value as near to zero as possible.

The QZVS occurs when there is not enough energy

plete analysis of the operation stages, as well as

available to reset the snubbers capacitors. The use of

the design procedures for the correct operation of the converter

auxiliary circuits with low cost and low reactive energy is the

are presented. Experimental results obtained from a prototype

main feature of QZVS.

of 250W/48V@100kHz demonstrate the feasibility of this Active Auxiliary Commutation Circuit (AACC) applied to two switches forward converter. Furthermore, a new concept of switching is introduced, where the main switches commutate with QZVS.

A great number of researchers have concentrated efforts to obtain converters with low commutation losses. As a result, converters operating with zero voltage and/or current switching have been exhaustively studied to reduce the drawbacks of hard commutation.

Hard commutation losses are mainly linked to three factors: the reverse recovery current of diodes; the discharge of the energy stored in capacitors parallel to the switch (specially in MOSFETs); the simultaneous occurrence of voltage and current on the switch during the commutation II. T HE Q UASI-ZVS S INGLE-ENDED F AMILY

In this section is presented the QZVS single-ended family

of non-isolated (boost, buck, buck-boost, SEPIC, zeta and

I. I NTRODUCTION

cúk) and isolated

(flyback, forward and two switches forward) converters. The basic converters of this family are presented in Fig. 1, and the state planes of these converters are presented in Fig. 3. A family with characteristics similar to the presented one was introduced in [7] with ZVS operation. However, under certain operating conditions, ZVS is not obtained. Anyway, with an appropriate design, the commutations can occur with QZVS. The presented converters allow QZVS in continuous conduction mode (CCM), discontinuous conduction mode (CCM) and critical conduction mode (CM). This can be seen C1 Lr Sa1 S1

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