Unfortunately, the answer to the blame question is beyond the scope of this article. What should be important is presenting the subject of electronics in such a way that makes it easy for anyone to learn. With that in mind, let’s take a look at one of those simple and
ubiquitous circuits: the transistor switch. Don’t worry, there’s nothing
more challenging here than multiplication, division, addition, and
subtraction. So, let’s begin!
A TRANSISTOR AS A SWITCH
Look at Figure 1. It shows a typical general-purpose (NPN)
transistor/LED circuit. If you hook up + 5 volts to Vcc in this circuit and
pulse the input terminal (Vin) with +5V, 0V, +5V, etc., the LED will flash
on and off accordingly. Of course, in order to make this circuit function
properly, you have to calculate the correct resistor values for RC and
RB. How do you do that? Well, keep reading.
Sometimes understanding how the simplest of electronic circuits work
can be intimidating and/or confusing for the student, hobbyist, or novice.
If I remember correctly (back in the 17th century), half of the people in
my electronics class dropped out after the first semester. Throw in a
course on calculus and you'll witness a raging stampede for the exit
door. Who do we blame for this abysmal dropout rate — students,
teachers, or curriculum? Andrew Carnegie was once asked, "What's
more important: labor, capital, or brains?" His reply was, "What's the
most important leg on a three-legged stool?"
By Roger D. Secura
May 2015 45