A basic understanding of electronic circuits is important even if the
designer does not intend to become a proficient electrical engineer. In many
real-life engineering projects, it is often necessary to communicate, and also
negotiate, specifications between engineering teams having different areas of
expertise. Therefore, a basic understanding of electronic circuits will allow evaluating
whether or not a given electrical specification is reasonable and feasible
Electronics is a know how of how to manage electrical energy. It deals
with electrical circuits and components like transistors, diode, resistors,
capacitors, amplifiers and integrated circuits.
In an MFC project it is of prime importance to consider the study of
electronics as it has a major role to play. A study to understand the basic
electronics components, it implementation and circuit designs is deemed to be
able to make optimal and reap maximum benefits.
In the following discussion,the basic components of electronics and its
implementation will be discussed.
An electrical component to create resistance in electric current is
called is Resistor.
The resistance value and tolerance are indicated with several colored
bands around the component body.
Fixed resistor symbolANSI standard
Fixed resistor symbol
Resistor color code
To determine the amount or magnitude
of the electrical current flowing around an electrical or electronic circuit,
we need to use certain laws or rules that allow us to write down these currents
in the form of an equation. The network equations used are those according to
Kirchhoff’s laws, and as we are dealing with circuit currents, we will be
looking at Kirchhoff’s current law, (KCL).
with a resistance of 5600 ohm with 2 % tolerance, according to the marking code
Temperature on Resistance
Change in temperature causes the resistance to change. This may happen
because temperature changes the dimension of a conductor. Also wires with high
thickness have less resistance and vice versa.
Resistors in Parallel
look how we could apply Kirchhoff’s current law to resistors in parallel,
whether the resistances in those branches are equal or unequal. Consider the
following circuit diagram:
In this simple parallel resistor
example there are two distinct junctions for current.
Kirchhoff’s First Law
per Kirchhoff’s law the charge entering a node is equal to the charge leaving
the node and the total current is zero. There is no loss of current.
Kirchhoff’s Current Law
A junction or a connection of two or more current
carrying routes like cables and other components is called as Node. Parallel
circuits can also be analyzed by Kirchhoff’s current law.
In the above figure, the currents I1, I2 and
I3 are entering the node are positive and two currents I4 and
I5 are negative. This can be expressed as:
I1 + I2 + I3 – I4 – I5 = 0
Kirchhoff’s Second Law
In any closed network the sum of voltage is equal to
zero if we do an algebraic summation of all the voltage across each loop.
Kirchhoff’s Voltage Law
can begin from one point of the loop and continue in the same direction,
clockwise or anti clock wise.
final voltage value will not be zero if the direction is not maintained. It has
to either clockwise or counter clock wise.
need to be clear with all the terms like
nodes, loops etc so that we can understand it for the AC and DC circuit
analyses base on Kirchhoff’s Current Law.
The total current in any part of linear bilateral
circuit can be calculated by evaluating the separate current by open circuiting
the current source and short circuiting the voltage source and summing them to
calculate the total current.
A two terminal combination of battery
and resistance can be replaced by a single current source and voltage source
across the terminals.
terminal collection of resistance and battery can be considered to be equivalent
to an ideal current source in parallel arrangement with a resistor. The value
of current can be derived by diving the voltage by r, where r’s value is same
as Thevenin’s equivalent.
A capacitor is designed by sandwiching an insulating
material between two metal plates. The insulation material in between is called
dielectric.The dielectric ensure there is not physical contact between the
Any material which is impede the flow
of current can be used as a dielectric. For ex; glass, plastic, rubber, paper
A capacitors capacitance depends on
how it has be constructed. More the surface are overlap, more is the
capacitance value, but lesser distance results into higher capacitance. Large
capacitors have higher capacitance value.
Below is the equation for total
In the above equation ?r is the
dielectric’s permittivity, d is the distance between the capacitor plates and A
is the area of the plates which overlap.
Charging and Discharging
capacitor is said to be charged when the positive and negative charged
accumulate on each plate, but could not meet as they are separated by an
At some point the plates become fully charged and hence cannot accept any
more charge. This is the maximum amount of charge a capacitor can hold.
If a path is created in the circuit
through which it could dissipate it discharges the capacitor and is called as discharging
Calculating Charge, Voltage,
The potential difference between the
plates determines how much charge can be stored in a capacitor. The equation to
depict the same is
V is the voltage applied, Q is the Charge store and C is
One Farad can be defined as the capacity to store one
unit of energy per one volt
Features of Capacitors
Different types of capacitors have
When deciding on capacitor types there
are a handful of factors to consider:
Size –Physical and
Maximum voltage –Each
capacitor has a voltage rating for ex 1.5 V. Exceeding it could be a destroy
Leakage current -. Every
capacitor leaks small amount of current through the dielectric. It is called leakage.
Equivalent series resistance (ESR) –The
resistance provided by the terminals of capacitor is called Equivalent
resistance. It is usually very small.
Tolerance –All capacitors
might vary from the ideal defined capacitance which could be from 1% to 20 %
This is one of the most commonly used
and produced capacitor. The name has been derived from the material from which
their dielectric is made.
Ceramic capacitors are usually small both
physically and capacitance-wise. Ceramic capacitor much larger than 10µF is
hard to find.
Two caps in a
through-hole, radial package; a 22pF cap on the left, and a 0.1µF on the right.
In the middle, a tiny 0.1µF 0603 surface-mount cap.
Compared to the popular electrolytic
capacitors, ceramics are a more near-ideal capacitor (much lower ESR and
leakage currents), but their small capacitance is a limitation.
Aluminum and Tantalum Electrolytic
These type of capacitors are good for high voltage
applications and they have a high capacitance and are relatively small. It
ranges from 1µF-1mF.It looks like a tin can with two leads at the bottom.
An assortment of
through-hole and surface-mount electrolytic capacitors. Notice each has some
method for marking the cathode (negative lead).
These are uniquely made to store very
High capacitance, but only rated for 2.5V. Notice these are also polarized.
These capacitors have very high
capacitance, but have relatively low voltage. A high voltage rating is achieved
arranging them in series.
Capacitors in Series/Parallel
Multiple capacitors can be combined
or parallel to create a combined equivalent capacitance. Capacitors,
add together in a way that’s completely the opposite of
Capacitors in Parallel
The total capacitance of capacitors in
paralleled is the sum of all capacitances. This is analogous to the way resistors add when they are in
For example, if you had three
capacitors of values 10µF, 1µF, and 0.1µF in parallel, the total capacitance
would be 11.1µF (10+1+0.1).
Capacitors in Series
Similar to resistors in parallel, the
total capacitance of Ncapacitors in series is the inverse of the
sum of all inverse capacitances.
If you only have two capacitors
in series, you can use the “product-over-sum” method to calculate the total
Capacitor Colour Code Table
Tolerance (T) > 10pf