The document introduces switches and their uses in power circuits. Switches come in mechanical and semiconductor forms and are used to provide functions like precisely regulated power supplies, polarity reversal, voltage conversion, and rectification between AC and DC circuits. Common approaches to achieve energy conversion include storing energy in a circuit element and delivering it to a load. While earlier analyzed circuits used switches ad hoc, a more general approach is needed to construct circuits methodically for different energy conversion needs. The document discusses taking a periodic switch action and device characteristics into account to better analyze and design power converters.

1. Introduction to Switches | Power Circuits
Power Circuits
Presenting the many facets of modern power electronics engineering.
Introduction to Switches
March 10, 2015 admin Leave a comment
We have seen that circuits involving switches and energy storage can be operated to give energy conversion functions. Switches come in a huge variety
including mechanical and semiconductor styles. It is important to develop a systematic way to identify appropriate power electronic circuits, and to find out how
they can be controlled to give the desired performance. Consider, for example, that circuits exist to:
● Provide a very tightly fixed DC output from an uncertain input voltage source. A power supply of this type can be used anywhere in the world without adjustments.
It must adapt itself to the available energy source while maintaining precise output.
● Provide polarity reversal. The is extremely helpful in bridging digital and analog electronics.
● Step a DC voltage up or down. The step up switching circuit we discussed previously an a kind of DC transformer.
http://powercircuits.net/introduction-switches/ (1 of 3) [4/16/2015 7:01:16 PM]

2. Introduction to Switches | Power Circuits
● Rectify, invert, and otherwise facilitate energy flow between AC and DC circuits, or between AC circuits acting at different frequencies.
The most common way to achieve these conversions is to store energy in a circuit element, then deliver it to a load to alter the voltage or current. Our
previously analyzed simple switching circuits from earlier posts offer a case study list for power conversion. In these circuits, the use of switches and energy
storage has been rather ad hoc. A few devices were interconnected and a power electronic function was asserted for the whole. We need a more general
approach to construct and operate circuits for energy conversion. The polarity reverser and the step-up circuits both operate by switching periodically with a 50%
on time. How will operation change as the on time moves from this 50% value?
One way to identify possible conversion circuits is to just write down all possible combinations of two or three switches, along with a few storage elements. This is
a real brute force approach and does not give insight into how we might make the best choise for a given function. But, there is a better way! We will be
concerned with basic tools for organizing and operating switch circuits. Once the switches have been organized, we will consider som of the device issues
that determine the behavior of converters. Diode circuits, for instance, can be analysed by taking the device behavior into account. A key element is that
switch action is periodic in time for almost all power converters. We will take advantage of this to develop tools for converter analysis.
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3. Introduction to Switches | Power Circuits
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