Analogue Electronics

Electrical concepts with mechanical analogues

Electrical Power

Energy dissipated by an electrical circuit

Voltage

• Voltage (V) is the potential energy that pushes

charge around a circuit.

• It is defined as:

“1 Volt provides 1 Joule of energy to each

passing Coulomb of charge”

• A helpful analogy:

Voltage is to an electron in a circuit what height is

to a ball on a hill.

Voltage sources

It is the … between

two parts of a circuit that makes

charges move

It is the potential difference between

two parts of a circuit that makes

charges move

voltage arrow points in the direction

of ...

More positive voltage

Different parts of a circuit will have

different ….

Different parts of a circuit will have

different absolute voltages.

Ground

Charge, Q

Charge (Q) is the fundamental quantity that means

electrons (holes) react to an electrical potential

difference (voltage)

• A single electron has a charge,

𝑞 = −1.6 × 10−19𝐶

Current, I

Current, I is the flow of discrete charges

𝑰 = 𝒅𝑸/𝒅𝒕

• It has a direction and a magnitude

• Current flows from ‘downwards’ in potential, e.g.

from areas of positive potential to ground

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Resistor

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Capacitor

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Inductor

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Semiconductors inc. diodes and transistors

Ohm’s Law

Ohm’s law states that the current flowing through

a conductor (I) is linearly proportional to the

voltage across it (V).

This proportionality constant is the resistance, R

(in Ohms, ). So that we write:

𝑉 = 𝐼𝑅

For materials that obey Ohm’s law, we

can write the power dissipation as:

Ohmic conductors

Materials with a linear V-I relationship

are Ohmic conductors, a good example

being metals. Resistors are Ohmic.

Non-ohmic conductors

Some materials or electronic devices

have non-linear V-I relationships. Many

semiconductor devices, e.g. diodes, are

non-Ohmic.

Resistance, R

Small resistors that you may have seen inside electronic devices are often made …

Small resistors that you may have seen inside electronic devices are often made Nichrome (‘high’ resistivity) thin films

Wires are often thicker, with high conductivity metals

Resistivity

The resistivity, , is a material property of

the conductor, and is a measure of:

• How many electrons are available…

• How easy it is to move electrons…

Designs must use

Preferred resistor values

Circuit Topology

Circuit connections

Parallel share common

Voltage

What is parallel with R2?

Kirchoff’s Current Law (KCL)

Kirchoff’s Voltage Law (KVL)

For a resistor, the voltage arrow points….

For a resistor, the voltage arrow points towards the

node where the current enters.

Combining resistors in series

Combining resistors in parallel

How do we write “parallel resistors”

Potential Divider

Current Divider method

What is the current Ib?

Steps of loop analysis

Steps are:
1. Identify a set of loops to allow solution of the currents of interest
2. Sketch voltages from loop currents
3. Apply KVL
4. Solve set of simultaneous equations

Identify loops

What if you get negative current when doing loop analysis?

It only means that the direction of current is opposite of what we guessed. Direction of loops really doesn’t matter

Identify V

Steps of nodal analysis

Find unknown voltages in nodes

A system is said to be linear when

When the above is satisfied, it is said

Graph of current against voltage of ohmic (linear) and non-ohmic (non-linear) behaviour

Superposition is used to

Steps of superposition

1. Linear

2. Found two sources