tailieunhanh - SWITCHING REGULATORS

The switching regulator is increasing in popularity because it offers the advantages of higher power conversion efficiency and increased design flexibility (multiple output voltages of different polarities can be generated from a single input voltage). This paper will detail the operating principles of the four most commonly used switching converter types: Buck: used the reduce a DC voltage to a lower DC voltage. Boost: provides an output voltage that is higher than the input. Buck-Boost (invert): an output voltage is generated opposite in polarity to the input | SWITCHING REGULATORS Introduction The switching regulator is increasing in popularity because it offers the advantages of higher power conversion efficiency and increased design flexibility multiple output voltages of different polarities can be generated from a single input voltage . This paper will detail the operating principles of the four most commonly used switching converter types Buck used the reduce a DC voltage to a lower DC voltage. Boost provides an output voltage that is higher than the input. Buck-Boost invert an output voltage is generated opposite in polarity to the input. Flyback an output voltage that is less than or greater than the input can be generated as well as multiple outputs. Also some multiple-transistor converter topologies will be presented Push-Pull A two-transistor converter that is especially efficient at low input voltages. Half-Bridge A two-transistor converter used in many off-line applications. Full-Bridge A four-transistor converter usually used in off-line designs that can generate the highest output power of all the types listed. Application information will be provided along with circuit examples that illustrate some applications of Buck Boost and Flyback regulators. Switching Fundamentals Before beginning explanations of converter theory some basic elements of power conversion will be presented THE LAW OF INDUCTANCE If a voltage is forced across an inductor a current will flow through that inductor and this current will vary with time . Note that the current flowing in an inductor will be time-varying even if the forcing voltage is constant. It is equally correct to say that if a time-varying current is forced to flow in an inductor a voltage across the inductor will result. The fundamental law that defines the relationship between the voltage and current in an inductor is given by the equation v L di dt 30 Two important characteristics of an inductor that follow directly from the law of inductance are 1 A voltage across an