Slave Converters Power Auxiliary Outputs TI（奴隶转换器功率辅助输出）.pdfVIP

LM1572 Slave Converters Power Auxiliary Outputs Literature Number: SNVA573 Technology Edge Reprinted with permission from EDN Magazine October 17, 2002, copyright Reed Business Information 2002, a division of Reed Elsevier Inc. Slave Converters Power Auxiliary Outputs By: Sanjaya Maniktala The age of creative thinking in dc/dc converters is not over. So-called new topologies may appear periodically, but if they are not resonant types, almost invariably they are just variations of the three primary topologies: buck, buck-boost, and boost. Fundamentally new topologies may well appear in the not-so-distant future, but even now you can create wonderful composite topologies from the primary topologies. The end game may vary. It could be either to eke out better performance from a single output converter or to generate auxiliary rails. A promising and cost-effective route for deriving auxiliary outputs is the concept of slave converters. This discussion deliberately takes a detour from the rather well-trodden path of placing several windings on a core to produce so-called regulated auxiliary outputs. This type of design may form the subject of some very clever patents, but the truth is that no one really likes anything other than easily available off-the-shelf inductors. So unless absolutely unavoidable, most engineers would prefer to use even several single-winding inductors rather than a tapped inductor, custom transformer, or a complex coupled inductor. Slave converters are symbiotic converters that run off the control waveform of a conventional PWM-controlled master converter and thereby share the same duty cycle and phase. The slave converter has no independent control circuit or a feedback node. It may use an active switch, but it may also just have coupling through a dc blocking capacitor to the master. Power-supply designers will immediately realize that it sounds like a pipe dream to expect any sort of