Posts Tagged ‘semiconductor’

Transistors – Voltage Regulation Part IX

Sunday, September 16th, 2012
     One way streets frustrate me, and I usually end up wasting a lot of time and gas driving in circles to get to my destination.  Generally speaking, I prefer a two way street.  Electric current flowing through electronic circuits is somewhat analogous to traffic flow.  There are circuit paths that act like one way streets and others that act like two-way.

     An electrical component called a diode can be used on circuit paths to govern the flow of current.  They are a key component in basic transistorized voltage regulator circuits, as we’ll see later.  For now, let’s get a basic understanding of how they work.

     Diodes are typically made of a semiconductor material, such as the element germanium.  These materials behave in a complex way that fall along the lines of quantum physics.  Esoteric phrases such as electron-hole theory, crystalline atomic lattice theory, and impurity doping are some of the concepts involved and would require a book onto themselves to explain.  For the purposes of this article all we have to know is that semiconductors have two properties.  The first property is that of an electrical conductor, that is, a material which allows electric current to pass through it.  Copper wire is a good example of this.  The second property is that of an electrical insulator, which blocks the flow of electric current.  Materials such as glass, wood, and rubber fall into the insulator category.

     A photo of a diode is shown in Figure 1, along with its symbol used in electrical schematics.

A diode and a diode schematic symbol.

Figure 1


     When electric current flows through a diode in one direction, as shown in Figure 2, the semiconductor material inside of it acts as a conductor, ushering it along a single path.

diode one way current flow

Figure 2


     When current tries to flow through the diode in the reverse direction, the semiconductor material acts as an insulator.  That is, it blocks the flow of current as shown in Figure 3.

diode stops reverse flow of electric current

Figure 3


     So we see that diodes can act like one way streets, restricting current flow.  But, not all diodes work this way.  Next week we’ll introduce a special kind of diode called the Zener diode, which allows current to flow in two different directions, and we’ll see how this functionality is put to work in regulated power supplies.


The Microwave Oven Becomes Reality

Sunday, July 31st, 2011
     The evolution of cooking methods has been interesting indeed, from the open fires of primitive man, who must have decided at some point that cooked meat tasted better than raw, on to wood fired stoves, fossil fuel-based cooking, whether coal, propane, or gas, and let’s not forget electric range tops.  Standing on its own in the modern kitchen is the microwave oven.  What will be next?  The space age food pill dispensing stations of the futuristic cartoon family, The Jetsons?

      We’ve been talking about resonant cavity magnetrons and the purpose they serve within a microwave radar system.  We also learned about Dr. Percy Spencer’s discovery and how microwave radar transmissions emanating from a magnetron can cook food, not to mention melt candy bars.

Figure 1- Microwaves Melt Candy Bars and Cook Food

     Although the technologies used in microwave radars and microwave ovens are similar, they do have important differences.  It would be both unsafe and impractical to install microwave radar systems into kitchens.  Radiation emitted from radar wave guide lacking proper containment would bounce aimlessly around the kitchen, posing a threat to human safety.  You see, microwaves don’t know the difference between our bodies and the food we wish to cook.  They’ll heat up human tissue just as readily as a bowl of chicken soup.  Another issue is that runaway microwaves lose much of their effectiveness through their aimless bouncing about, and much of it would not be directed to the food itself.  Dr. Spencer would learn how to corral that energy, making microwave cooking a commercial success.   

     The biggest problem for Dr. Spencer to overcome was containment of the microwaves.  They needed to be directed towards food in order to efficiently heat them.  His first microwave oven was a metal box containing an opening at the top into which a magnetron wave guide could be inserted.  This would then introduce microwaves into the box, and the metal construction of the box would safely contain them.  The safety issue had now been resolved because the waves couldn’t escape, they would simply bounce around inside the box and most of their energy would be transferred into any food placed inside.

     Dr. Spencer’s employer, the Raytheon Corporation, produced the first commercial microwave oven in 1954, and it was appropriately named the “Radarange.”  It was huge, almost six feet tall, and weighed in at about 750 pounds!  Hardly something that could fit into a home kitchen.  Despite its massive size, the Radarange wasn’t all that powerful and couldn’t compete against the compact countertop microwave ovens in use today.

     It wasn’t until 1967 that technology improved enough to give us the smaller, more efficient units affordable to consumers.  This improvement involved using a newly developed semiconductor device called a “diode” within the high voltage electric circuitry that powers the magnetron.  We’ll learn more about these technologies in our next post.

     Also in our next post, we’ll see how high voltage circuits can pose electrocution hazards in a way you‘d never expect.  I discussed one of these instances in my recent appearance on The Discovery Channel program, Curious and Unusual Deaths, soon to be aired.