## Review of Fourier Series

Nearly any periodic function of time , such that , can be written as a sum of sinusoids known as the Fourier Series. where the radian frequency is defined as . This result applies to signals with jump discontinuities which are often encountered in the world of power electronics. While there are few very special periodic functions without Fourier Series […]

## Characteristics of Power Semiconductor Devices

Diode – Current ratings from under 1 A to more than 5000 A. Voltage ratings from 10 V to 10 kV or more. The fastest power devices switch in less than 20 nanoseconds, while the slowest require 100 microseconds or more. The function applies in rectifiers and DC-DC circuits. BJT – (Bipolar Junction Transistor) Conducts collector current (in one direction) when […]

## Kirchhoff’s Voltage and Current Laws

Granted, a switch circuit can perform power conversion, and granted, it can be described as a switch matrix. How do we make the choices of switch operation? Consider first the simple circuit shown to the right – something we might try for AC-DC conversion. This circuit has problems. Kirchoff’s Voltage Law (KVL) tells us: The sum of voltage drops around a […]

## Introduction to Switches

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, […]

## Recap of Power Electronics

Power electronics involves the study of electronic circuits intended to control the flow of electrical energy. These circuits handle power flow at levels higher than the individual device ratings. Energy conversion is our business because people use light, mechanical work, information, heat and other tangible results of energy – not electricity itself. In most electronics, devices are limited by their […]

## Filtering a Switched Power Supply

As seen in the previous post, a simple switch or diode rectified output is still not a clean DC signal. The waveform contains AC components on top of the DC offset. The simplest methods for smoothing this output involve filtering through the use of passive storage elements such as capacitors or inductors. In essence, these components tend to smooth the […]

## The Effect of Phase on Switching Rectifiers

In the previous post, we examined some of the most basic switch based rectifying circuits and saw that the switch could be replaced with a passive diode. Here, we will explore what happens when the switch is no longer in phase with the input. Let us consider a different way to operate the switch. Using the same circuit as the […]

## Basic Power Conversion Examples

Let’s look at a few examples of power electronic systems. Consider the circuit shown below. It contains an AC source, a switch, and a resistive load. It is therefore a simple but complete power electronic system. Just to get an idea of how power conversion might take place, let us assign some kind of control to the switch. What if […]