Talk:Circuit Idea/How to Make Perfect Components

Here is the building "scenario" that my students from group 68b and I were using during laboratory excercise about the op-amp circuits with parallel negative feedback (op-amp inverting circuits). Circuit-fantasist (talk) 18:03, 26 April 2008 (UTC)

Lab 4: How to make perfect components by parallel NFB
Thursday, April 24, 2008, 16.45 h

Is the real diode a perfect component?


A forward voltage drop VF appears across a real diode when a current flows through it... What is this voltage drop - useful or harmful? Sometimes it is useful; other times it is harmful...

"Useful" examples. When we make voltage stabilizers, we need this voltage drop. In these cases we do all that is possible to create and increase this useful voltage drop appearing across various diode component: diodes, LEDs, zeners, multiple diodes connected in series...

"Harmful" examples. In other cases, when we use a diode as a switching element, we do all that is possible to remove and to remove this harmful voltage drop... Then we need an ideal diode without forvard voltage drop VF...



Making the simplest parallel diode limiter


Why do we connect a reasistor R between the input voltage source and the diode (load)?

What does the combination (VIN + R) represent? What is it?



Deriving the basic idea from our human routine
(write here all the situations in your daily routine where you have remove all the obstacles standing in your way:) Circuit-fantasist 06:36, 26 April 2008 (UTC)

Implementing the powerful idea into an electrical circuit








What have we actually done here? How does it operate? What is the final result?

The answer is amazing: we have made just... a piece of wire...?!? What do you think about this speculation? Is it always right? Circuit-fantasist (talk) 06:59, 26 April 2008 (UTC)



An op-amp acting as a varying voltage source
What can act as a varying voltage source in our electronic circuit? What can "help" the imperfect diode by adding so much voltage as it loses across the diode? At last Lab 3 we were using transistors for such a purpose; let's now, for the sake of change, use an op-amp...



Now the op-amp has to "insert" the "helping" voltage VF into the circuit; so, how to connect it?

Finishing the op-amp circuit
Eureka! We have invented an (almost) ideal diode without (any) forvard voltage VF!

















...multiple diode voltage drops...






...zener diode voltage drop...






...resistor voltage drop
With the same success we can destroy the "harmful" voltage drop across a resistor. What a circuit can we "invent" in this way? Write its name here....

Making the harmful voltage drop act as an input




Generalizing the powerful "helping" idea


We are already true magicians as we can transform any imperfect component into an almost ideal one! In this lab, we have transmuted a real diode (ordinary, LED, zener, any combinations of them, etc.), a resistor and a photoresistor into... a piece of wire:) having no any voltage drop across it! But with the same success we can make a "botomless" capacitor (an op-amp inverting integrator)... For this purpose, we just incorporate a varying battery to the imperfect component that compensated the losses inside the component. All the op-amp inverting circuits exploit this clever trick.



Resources
How do we create a virtual ground? is a circuit story about the great phenomenon. Op-amp inverting current-to-voltage converter reveals the basic idea behind the famous circuit. How do we build an op-amp ammeter? is a similar story about the active ammeter.