Electronics in IT Lecture

Voltage

Difference in electric potentials between two points in space

Currents

Flows when two points of different electric potential (e.g. the battery terminals) have a conductive medium between them

Density of electron flow in conductive medium

Conventional current

Arrow in a schematic

Flows from the higher to lower electric potential, regardless of medium

Actual current

Uses charge carriers (any freely moving charged particles) to propagate the electric field

Metals

Have freely roaming electrons as charge carriers

negatively charged, higher

Electrons are _____ charged and attracted to the node with _____ potential

From - to +

Describe the flow of electrons in wires

Voltage Source

Voltage is constant, tries to deliver as much as the load draw

Batteries, accumulators, USB power, AC-DC wall wart adapters

Current Source

Current is constant, tries to adjust the voltage to have the load draw the correct current

Mostly occurs inside chips or as part of very specific circuit steps, test equipment

Conductor

Abundant charge carriers

High conductivity  → low electric resistance 

Usually is a metal, e.g. copper, aluminum

Used to create electric connections between components, devices, etc.

Insulator

No free charge carriers

Low conductivity  → high electric resistance

Usually is a compound, e.g. rubber, mineral oil, …

Used to ensure no electric connection happens between components, devices, and especially people and wires

Will become a conductor at high enough voltage

Voltage source

Identify the symbol

Current source

Identify the symbol

Crystal structures with abundant charge carriers

What type of structure do conductors usually have?

~17 nΩ/m (17 × 10⁻⁹ ohms per meter)

What is the resistance of copper per meter at room temperature?

It vibrates more, causing electrons to bump into stuff instead of flowing on

What happens to a metal’s crystal lattice when temperature increases?

Worse

Do metals conduct better or worse when heated?

Air

What is an OK insulator for smaller voltages?

Rubber and plastics

What are some good insulators for higher voltages?

Batteries, PSUs

Voltage sources with predefined max. current they can deliver, exceeding that current may lead to shut-off or overheating

Semiconductor

A so-so conductor and so-so insulator

Optical Semaphore

A system of towers using visual signals to transmit messages limited by earth’s curvature and obstacles (hills, mountains)

Claude Chappe

Who coined the word Telegraph and invented the Optical Semaphore Line?

Electric Telegraph

Invented to battle issues posed by the earth’s curvature and terrain and improve the process

Telegraph

Applicable to any technology that allows fast propagation of information over a distance

Galvanometer

A device that shows if current is flowing through a conductor

Makes use of electromagnetism: a wire shaped into a dense coil becomes an inductor

When current flows through an inductor, it creates a proportional magnetic field: This field can be detected with a permanent magnet, e.g. a compass needle

A breakthrough product of early research on electricity

High resistance weakens the signal

What problem occurs in long telegraph wires of the electric telegraph?

Using re-amplification

How was weak signal over long distances solved?

Electric relay

Mechanic switch actuated by an electromagnet

Extremely simple in construction

Industry standard for re-amplifying telegraph signals

Simple construction, mechanically robust, can pass a lot of current

Pros of Electric Relays

Faster than towers but still speed-capped, Has moving parts (mechanical) that will deteriorate over time, Can malfunction due to high current welding the switch

Cons of electric relays

Vacuum tubes

Served a similar purpose as relay but it is purely electronic, not electromechanic: boost in speed, better reliability, resistance to weather

Tubes are lambs and burn out

Major drawback of vacuum tubes

Seebeck effect

A phenomena where some materials (e.g. silver sulfide) drop resistance when heated up and create an electromotive force when heated unevenly

copper/copper oxide (metal-semiconductor)

What kind of junction rectifies AC (removes the negative half)?

Russel Ohl

Observed a difference in resistance between zones of a germanium crystal containing different impurities

He found a P-N junction: a diode

Solid-state electronics

No moving parts or vacuum tubes

Silicon, Gemranium, Gallium Arsenide

What are some famouse semiconductor materials?

Silicon has 4 valence electrons

Forms 4 covalent bonds with neighbors

Each atom effectively has 8 outer electrons

No free charge carriers → poor conductivity

Explain Silicon’s rigid structure

By adding phosphorus (adding an atom of many electrons)

By adding boron (adding an atom of few electrons)

= Doping

How can we make silicon conduct better when it has no free charge carriers?

N-type semiconductor

Doped semiconductors with free electrons and negative majority charge carriers

P-type semiconductor

Doped semiconductors with free holes (electron absences) and positive majority charge carriers

P-N junction

Having a P-type semiconductor next to a N-type semiconductor

Free holes from the P side meet free electrons from the N side at the border, they recombibe

What happens when the PN junction is created?

Depletion Zone

This is a result of the recombination of free holes and free electrons in a P-N junction border

An electromagnetic field emerges

What emerges because of the difference of potentials of atoms in a P-N junction border?

context:

The atoms on the P side of the depletion region together hold a negative charge now (too many electrons)

The atoms on the N side now hold a positive charge (too many holes)

Charged ions

What appears when particles diffuse in an electromagnetic field (emf opposes diffusion)?

Barrier voltage is formed

What happens when diffusion in emfs reach equilibrium?

0.7 V

Potential difference in depletion zone of silicon PN junctions

forward-biased diode

positive voltage applied to P side and negative to N side → current flows

reverse-biased diode

positive voltage applied to N side and negative to P side → no current flows