Basic Electronics - Diodes and Transistors
Basic Electronics
I wrote a course that I presented to college level students back in the 90's. It covers a basic understanding of how Integrated Circuits worked. Since then, the technology has improved significantly, but the basics remain the same. I'm going to try to break the course down into digestible segments for those who'd like to read it.
I plan to break it down into the following posts :
Hole Movement and Current
Voltage and Resistance
Capacitors and Inductors
Diodes and Transistors
Logic Gates
Flip-Flops and Memory
To Be Determined
Diodes and Transistors
Ideal Diodes
- A diode is a one way valve for current.
- An ideal diode does not create a voltage drop.
- If the current flows from the anode to the cathode, the diode acts as a short circuit (piece of wire).
- If the current tries to flow from the cathode to the anode, the diode acts as an open circuit.
If you think of a funnel with a plate attached to the narrower end. If you tried to spray a hose on the plate, most of the water would bounce off. But if you sprayed the water into the funnel, most of the water would continue to the other side.
If you can remember this image, you can remember which direction the current flows through a diode.
Real Diodes
- Diodes made of silicon are called Junction Diodes. - Junction diodes require some voltage to switch them on. (Usually around 0.7 Volts)- This is known as a diodes junction voltage.
- Zener diodes take advantage of this breakdown and provide a means for inexpensive voltage regulation.
- the zener diode will remain off until you reach the breakdown voltage, then it will turn on.
Some Uses for Diodes
- Some Common uses for diodes are:- current direction control
- voltage regulation
- rectification (A cheap way to turn AC into DC)
- REMEMBER: If there is a higher voltage at the Cathode than the Anode, the diode will be on. This is fundamental for the concept of transistors.
Transistors
- A transistor is essentially a diode with a switch. - When you close the switch, the current flows through. When you open the switch, the current stops. - To activate the switch, apply a voltage or a current to a third pin. - Similar to the gas pedal of a car, a little bit of pressure (voltage) on the control pin can control a lot of power ‘under the hood’. 
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NPN and PNP
- There are two major types of transistor, BJT’s, and FET’s. For the purpose of this course, we will only discuss FET’s - There are two basic configurations of transistors, NPN and PNP - Think of them like two light switches. For the first, you flip it up to turn it on. For the other, you flip it down to turn it on. - The basic difference is:- To turn an NPN transistor on, the source must have a higher potential than the gate
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- To turn a PNP transistor on, the gate must have a higher potential than the source
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Transistor as an Amplifier
- By controlling the gate current to the transistor (by adjusting Radj), you can control the current flowing through the load resistor (Rout) at Vout 
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Transistor for Digital Logic
- As an amplifier, the transistor is acting in an analog fashion, where the output voltage can be one of an infinite number of values - If we set a cut-off point for the voltage, rearranging our mindset so that any value below that cut-off point is “LOGIC ZERO” and anything above that cut-off point is “LOGIC ONE”, we are now delving into the world of digital electronics.References
Capacitor
Farad
Inductor
Flux
Diode
Transistor
I found your article pretty interesting as an introduction to electronics. However, I'm wondering if you could do a post on real world applications with the knowledge. I would like to learn how to build a circuit board with the various parts you mentioned just for fun. Any ideas how I should start?
You are one post ahead of me. 😊
In the next post, We will start to see practical uses.
What would you like your circuit board to do?
I'm thinking of controlling the lights to be motion controlled. Instead of buying those ready made in the market, I'm wondering if I can create one myself. :D
Have you looked at a kit for instructions?
http://www.instructables.com/id/Make-An-Simple-Motion-Sensor-Light-PIR/
http://www.learningaboutelectronics.com/Articles/Motion-detector-circuit.php
But, if you want to control regular voltage lights, you need an interposer circuit between the low voltage sensor and the high voltage lights. That gets a little more complicated.
thanks for the information. I'm a beginner and I have no idea what an interposer circuit is but I'll Google it. Unless it's way more complicated than what I think it is, I'll have to resort to buying one from Amazon or Home Depot.
If you are dealing with 120V or 208V, then I strongly recommend buying it for one simple reason. If something happened, and your house burned down, insurance wouldn’t cover it.
alright. I guess I'll stick with Home Depot.
best technolog post.
Thank you for taking the time to post this information. I think the explanation and examples for diodes are great. There is more to consider, but you have done a great job at providing enough real world parameters without information overload.
I have a recommendation on the transistor part. While all semiconductors are built with either P-Type and N-Type materials, and as you mentioned there are two categories of transistors. One type is the FET (Field Effect Transistor) and another type is the BJT (Bipolar Junction Transistor). The FET you described is either N-channel or P-channel. In other words the NPN and PNP relates to the structure of the BJT type rather than a FET.
FETs are voltage controlled devices that have channels that deplete or enhance to control current. The BJT is current controlled and closer resembles the diode in terms of bias.
There are more sub-classifications, especially with the FETs, but as mentioned you have done a great job avoiding information overload and I look forward to more work.