Understanding Circuits on the Whiteboard...

# What is the idea behind circuit?

 Welcome to Understanding Circuits on the Whiteboard! As far back as I can remember - as a student and a beginning teacher - I was trying with no success to penetrate into electronic circuit phenomena using classical textbooks on electronics. With time I have reached the conclusion that formal methods do not explain circuits. What is more, mathematical methods may even lead us to absurdity analyzing something, not really knowing what it is. Only, I have never wanted to think in a formal way, as I am a human being, not a computer. That is why, I have gradually built my own simple philosophy of understanding: 1. Electronic circuits, irrespective of their complexity, are based on clear and simple basic concepts, which may be derived from our routine. 2. In order to really understand circuits, we have first to reveal the basic ideas behind them. Drawing colored pictures on my favorite whiteboard (see the legend), I will show the basic ideas behind circuits in a way that you have never seen before! I have extracted these ideas from many years of thinking; they are my great circuit penetrations, my truth about circuits. I hope they become your truth too. I have started this part of Circuit Stories on the Whiteboard especially for you - creatively thinking students, hobbyists and for all those who do not feel happy with traditional formal explanations of circuit phenomena. Only, if you are curious enough, you may then come to know how to build and why not how to invent these circuits? As a result , following this 3-step "scenario", you will be able gradually to understand, present and even invent any (even completely new) electronic circuit! It sounds wonderful, isn't it? Well, are you ready? Let's begin!

### What is the idea behind constant current sources?

A philosophy:

What is the idea behind a constant current source?

Passive compound current sources:

Simple current source (shortened)

Simple current source (real loaded)

Active current sources with varying the internal resistance:

Simple BJT current source

Active current sources with varying the excitation voltage:

Transistor current source with shifting diode

Transistor current source with shifting capacitor

Widlar op-amp current source

Active current sources with adding a voltage:

Inverting op-amp current source

Active current sources with adding a current:

Howland op-amp current source

### Stories About Negative Resistance

to be continued...