Is there a simple, intuitive way to design transistor circuits?

Question

For the clever engineers...its obviously to design transistor/amplifier circuits with complex math tools (Spice, matrix equations, etc)

Is there a drastically simpler way to do this?

What I had in mind is a more intuitive approach and just building it up piece by piece without resorting to complex full circuit analysis.

I often see these extremely complex circuits (eg like the inside of an Op Amp) and think, how could I break this up and figure it out in a few minutes without some horrendous difficulty?

What might a simple approach look like? Im not adverse to a little math...but something drastically simpler.

Thanks for any intuitive insights.

What comes to mind is some new way of looking at a transistor or component that is extremely obvious and speeds design to a very quick intuitive level...thanx again

one futher idea: Im thinking lego blocks here...lego blocks of transistors...

Answer 1

This may not seem like a direct answer to your question but maybe this link might be helpful in that it might lead up to the general area or spark some idea of your own. Actually I was trying to remember a source for things that followed an old process of painted circuitry etc. but couldn't find it right away.

http://www.anti-theory.com/texts/Sound_on_Sound/

Anyway it might not be exactly what you had in mind but could be fun.

Answer 2

First of all, I think you are confusing design with analysis which in the electrical world is like comparing a tonka truck to a Ferrari. I am going to assume you are talking about analysis. Transistors are not the easiest things to intuitively understand. They are highly non-linear devices and we are trying to make them work in a small linear range. That why they make op-amps but I will try to explain what I know.

Well the first approach would be to known what type of transistor you are looking at(i.e. BJT, MOSFET etc). If they are used as switches it shouldn't require any calculations at all. Just determining which ones are on and with ones are off. If they are amplifiers you can use some estimations to determine the gain for small signal analysis. These are only estimation and can sometimes be very far off.

Truly the best way to get a good understanding of transistors is to use them. Try building circuits (lab or PSpice) and examining how they work and their limits. Also build transistor circuits you find in books and look at how they work. An important point to make is that all transistors are little different. Transistor are hard to get a really good understanding of how they work so you can design complicated systems with them. That is why they pay people a great deal of money to design transistor circuits.

I wouldn't worry about much more than 4 or 5 transistors in circuit that isn't using them as switches. That would be truly mean of your professor.

Answer 3

For bipolar junction transistors:

My approach was always to use a basic amplification circuit using an (unbypassed) emitter resistor and collector resistor. The gain of that circuit is the ratio of collector resistance to emitter resistance, and does not depend on the beta or other transistor parameters. Other circuits can be designed using the following simplified principles:

Emitter current = base voltage / emitter resistance. (As long as bse voltage >> emitter drop of about .7 volts)

Collector current = emitter current

Collector voltage = -collector current x collector resistance

Answer 4

You have two basic choices;

1. Accept that transistors are simplified models of physical events, be happy and build from there.

OR

2. Keep breaking things down to smaller and simpler elements until you can explain the universe in the 5 universal forces that hold it together;

The Strong Nuclear Force that holds neutrons and protons together to form atomic neucli

The Weak Nuclear Force that holds gluons together to form neutrons and protons

ElectroMagnetism that holds neutrons, protons and electrons to form all matter around us.

Gravity that holds all of the pieces of the universe together

and most critical of all: Duct Tape

Once you've mastered that, you can develop the Grand Unification theory that all the Physicists have been looking for for decades.

Good Luck!

Answer 5

The essential thing is to realize that a transistor is essentially a switch. It works by changing its resistance from "very high" to "very low". The ground state is "very high" which means "off" which means almost no current gets through the collector. When a small voltage or current is applied to the base electrode, the transistor switches to "very low" or "on" which allows a lot of current through the collector.