Power Electronics is that part of the electronic spectrum devoted to the design and  implementation of circuits that drive large loads, like 1 watt and above. Examples are power  supplies and modules; speaker drivers; motor drivers; solenoid drivers; illumination control;  inverters; battery chargers and battery backup systems; and many other applications.

 Why is it different?

 The parts used are power MOSFETs and transistors, SCRs and triacs, IGBTs, large diodes, power  transformers, all usually requiring some sort of heat sink and maybe a fan for cooling.  Associated lower level parts, such as drivers for the power stage, can be what are used in  other electronic products but do not require anything special for their general operation.  This  could include digital parts.

 So the power level in question defines the type of part used. The design engineer must decide  this as an element of the specification for the circuit block.

 Sometimes power filters need to be designed for cases where they are in the direct power path.  Power Electronics provides the circuitry to handle, route, modify and control power from the  power source to the load.

 Historical perspective

 Before semiconductors became available, power was handled by large vacuum tubes, some  containing mercury, and rectifiers made of selenium deposited on large metal plates.  Transformers were made of silicon steel (many still are) operating on the 60 HZ line. Gas  filled tubes were available to regulate the high voltages needed for amplifiers of the day.  Efficiency was unheard of, because these monster power handlers were lossy and so one just  would draw whatever power needed to operate the load device. Later, multigrid tubes became  available to be used in a feedback circuit arrangement to regulate d.c. voltages.

 Today we are looking for 50-100 watts/square inch power supply density. Back then it was more  like 1 watt/square inch, with power supplies starting with the size of a shoe box and possibly  consuming the size of a large rack. Due to the heavy weight of the power transformers used,  power supplies were always mounted on the bottom of the rack of electronic equipment to keep  the rack from tipping over.

 Mobile electronics were powered by something called a dynamotor, that operated off the 6 volt  car battery. Mechanical vibrators (choppers) were also used to produce a.c. square waves that  could then be amplified with transformers and then rectified, producing the required d.c.  voltages. The dynamotor had greater power capability, and was used in police cars to drive  their high powered transmitters. As you might expect, these electro-mechanical devices had a  high failure rate.

 World War II brought on the evolution of electronics, spawning a profusion of electronic  companies of many types.

 Thus, elements of Power Electronics go back to the beginning of the electronic sciences. Parts  are now smaller and more efficient. We now expect low cost, low volume, low weight, low noise,  and high efficiency.