Buck

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Buck

Aplicação do Modelo Linear de Vorpérian ao Conversor tipo Buck
Ewaldo L. M. Mehl
1. Apresentação
Com o uso do conceito do “Interruptor PWM” apresentado por Vorpérian [1,2], torna-se extremamente simples e rápida a simulação de conversores estáticos DC-DC utilizando modulação por largura de pulso. O presente trabalho mostra o uso dessa técnica através de simulações de um conversortipo Buck, usado como exemplo, usando o programa PSpice.
2. Exemplo de um Conversor tipo Buck
Na Figura 1 tem-se o circuito básico de um conversor DC-DC tipo Buck (abaixador de tensão). O interruptor S1, mostrado na Figura 1 como um transistor bipolar, pode ser implementado com diversas tecnologias de dispositivos semicondutores, tais como MOSFETs ou IGBTs. A fonte de tensão Vg representa atensão DC de entrada, sendo a resistência R a carga do conversor.
Figura 1: Circuito de potência de um conversor DC-DC tipo Buck |
Application Report
SLVA059A - March 1999 − Revised November 2002
1
Understanding Buck-Boost Power Stages in Switch Mode
Power Supplies
Everett Rogers System Power
ABSTRACT
A switching power supply consists of the power stage and the control circuit. The powerstage
performs the basic power conversion from the input voltage to the output voltage and includes
switches and the output filter. This report addresses the buck-boost power stage only and
does not cover control circuits. Detailed steady-state and small-signal analysis of the
buck-boost power stage operating in continuous and discontinuous mode is presented.
Variations in the standardbuck-boost power stage and a discussion of power stage
component requirements are included.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Buck-Boost Stage Steady-State Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 3
2.1 Buck-Boost Steady-State Continuous Conduction Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Buck-Boost Steady-State Discontinuous Conduction Mode Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Critical Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3 Buck-Boost Power Stage Small Signal Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1 Buck-Boost Continuous Conduction Mode Small-Signal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Buck-Boost Discontinuous Conduction Mode Small-SignalAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4 Variations of the Buck-Boost Power Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.1 Flyback Power Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5 ComponentSelection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1 Output Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.2 Output Inductance . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3 Power Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.4 Output Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....
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