Everything you ever wanted to know about a diode but were too afraid to ask

What is a diode?   A diode is a semiconductor device that allows current to flow in one direction but not the other. The type of diodes discussed here are general use diodes commonly called blocking diodes although there are many different types.  The best way to think of a diode operation is as a switch.  When forward biased the diode acts like a closed (on) switch, and when reverse biased the diode acts like an open (off) switch. We will talk about what forward and reverse bias mean in a minute.              

           Above is the electrical symbol for a diode

Above is a picture of an actual diode the banded side is the cathode side

 

 

 

 

For an examples look at the diagrams below:

Example #1

Example #1shows a diode placed in a lighting circuit.  With the diode placed forward biased the anode is on the positive side and the cathode on is the negative as shown above, the diode lets the current through thus lighting the light.

Example #2

Example #2 shows a diode placed in the same circuit except that this time it is placed reverse biased with the cathode on the on the positive side and the anode on the negative. A diode that is reverse based will not let the current through which will leave the light off.

Ok, so now we know how a diode works lets apply it in a circuit that puts it to good use. See Example #3 below.

Example #3a

Example #3b

With example #3a we see a light that can be powered by two different voltage sources.  If power is applied to source #1 voltage goes through the forward biased diode #1 to the light and can not migrate back to voltage source #2 because the 12volts going to the cathode side makes diode #2 reverse biased in this situation and vice versa if power is applied to voltage source #2 as shown in example 3b. (Refer to back to example #1and example #2 if this is not clear to you)

A diode is needed on both power sources so that voltage cannot migrate from one source or device to another. In a circuit similar to example #3 take a look at example #4 below it has no diodes in place and will have voltage going places you probley don’t want it to go.  This can power up things that shouldn’t be powered and can even burn up things (once you have let the smoke out of something you cant put it back).

Example #4

Wrong!!!!!!  

I hope this little lesson has enlightened you on how a diode works.  Tune in next week where will be learning the effects of peeing on an electronic fence charger.                                                          

                                                 He had it comming don't you think?                                                

                                      

Courtesy of TS member Superman