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
Tolerance (T) < 10pf Temperature Coefficient (TC) Black 0 0 x1 ± 20% ± 2.0pF Brown 1 1 x10 ± 1% ± 0.1pF -33×10-6 Red 2 2 x100 ± 2% ± 0.25pF -75×10-6 Orange 3 3 x1,000 ± 3% -150×10-6 Yellow 4 4 x10,000 ± 4% -220×10-6 Green 5 5 x100,000 ± 5% ± 0.5pF -330×10-6 Blue 6 6 x1,000,000 -470×10-6 Violet 7 7 -750×10-6 Grey 8 8 x0.01 +80%,-20% White 9 9 x0.1 ± 10% ± 1.0pF Gold x0.1 ± 5% Silver x0.01 ± 10% Metalised Polyester Capacitor Usually the capacitors have 2-3 number and an optional tolerance letter code The two numbers is used to determine the value of the capacitor and is in picofarads. The third letter code is multiplier similar as resistors. For example, the digits 531 = 53´10 = 530pF. Three digit codes are often accompanied by an additional tolerance letter code as given below. Capacitor Tolerance Letter Codes Table Letter B C D F G J K M Z Tolerance = C<10pF±pF Diode Unidirectional flow of current occurred due to a diode which is functional in rated specific voltage intensity. The main function of diode is to oppose current in opposite direction. The voltage at which it breaks is known as reverse breakdown voltage. Rectifier Alternating Current (AC) is exchanged into a Direct Current (DC) through a rectifier which is an electrical device and use one or more P-N junction diodes with precise array. The forward bias is when positive terminal connect with P-type and negative terminal connect with N-type and voltage is given to the P-N junction. When P-type is joined with –ve terminal and N – type is joined with +ve terminal and the voltage is applied to the P-N junction diode, it is called reverse bias. Rectifier types: Half wave rectifier Full wave rectifier Bridge rectifier Half wave rectifier The rectifier which converts half of the AC input signal (positive half cycle) into DC output signal and the remaining half signal (negative half cycle) is lost is known as half wave rectifier. In half wave rectifier circuit, only one diode is used. Full wave rectifier The full wave rectifier transfer the full AC input signal (positive half cycle and negative half cycle) to pulsating DC output signal. The efficiency of full wave rectifier is high as compared to the half wave rectifier. Bridge rectifier Alternating Current (AC) converted into Direct Current (DC) proficiently through Bridge rectifier which utilizes four or more diodes for circuit design. In this configuration it converts the full AC input signal into pulsating DC. Bridge rectifier construction Below is the construction of bridge rectifier. Alternating Current (AC) convert into Direct Current (DC) current by connection of four diodes in a closed loop in bridge rectifier. The benefit of the bridge rectifier configuration is so as to, it does not need an expensive center tapped transformer. Hence it reduces the cost and size. Functional properties of bridge rectifier When input AC signal is applied across the bridge rectifier, positive diodes D1 and D3 are arranged in forward biased and thus permit electric current to flow, but diodes D2 and D4 are oppose flow of electric current as they are arranged in reverse biased. During the negative half cycle diodes just opposite was happened. From the above two figures, we can observe that the flow of current direction across load resistor RL is same during the both half cycles. Therefore, the polarity of the output DC signal is same for both positive and negative half cycles. . Bipolar Transistor When two PN-Junction diodes are connected in series, either a P-Type or N-Type material gets sandwiched. This creates three terminal, two junction device called Bipolar Junction Transistor BJT. Transfer and Varistor combines to create the word Transistor. It describes their mode of operation in their early days of electronics development. The two types of BJT PNP and NPN are based on the physical arrangement of the semiconductor material p-type and n-type.It has two PN junction and three terminals Emitter, Base and Collector. It controls the current flowing through it and are current regulating devices. The current flow is proportional to the biasing voltage applied to the base terminal. The working of both types of transistors PNP and NPN are same and they only differ on how they are biased. Bipolar Transistor Construction The circuit arrangement for both the PNP and NPN are given below. Same as diode the direction of the arrow is same from P-type region to N-Type. Bipolar Transistor Configurations As we know it is three terminal device all the three terminals are connected in an electronic circuit differently where one terminal is common between the other two and hence named as. Common Base Configuration (CB) – This setup has Voltage Gain but no Current Gain. Common Emitter Configuration (CE) – In this configuration the circuit has both the Current and Voltage Gain. Common Collector Configuration (CC) – Opposite to CB configuration it has Current gain, but no voltage gain. The Common Base (CB) Configuration In this setup the base terminal is common and the input is provide from the base and emitter terminal, whereas the output is the measured from base and collector. The Common Base Transistor Circuit The CB is a voltage amplifier with a non-inverting output. In this type of set-up the phase of the input and output voltage are same. This is not very less likely used configuration due to the high voltage gain. Common Base Voltage Gain A common use of the this circuit is in microphone or radio device due to its high frequency response. In the above formulae Ic/Ie is the current gain, alpha ( ? ) and RL/Rin is the resistance gain. The Common Emitter (CE) Configuration In a CE configuration the emitter terminal is common between the base and collector. The input signal is applied through the base and emitter whereas the output is measured through collector and emitter terminals. Due to its moderate voltage and current gain properties it is more used in the different electrical circuits. Transistor Biasing If a transistor is to operate as a linear amplifier it has to be biased to have a suitable operating gain. The operation of a transistor can be controlled by the base current, collector voltage and collector current Fixed Base Biasing a Transistor When the IB remains contact for a given value of Vcc it is called fixed bias. Transistor Biasing with Emitter Feedback When a transistor circuit is the set up in a way that it uses both base collector and emitter has feedback to stabilize the collector current is said to be in Emitter feedback configuration. Voltage Divider Transistor Biasing A setup to use voltage divider network to stabilize in the CE configuration is called Voltage Divider. As we can see in the above image that the two Resistors Rb1 and Rb2 are forms a voltage divider network across the supply. Operational Amplifier A set-up to amplify DC/AC signals and performing operations like add, subtract, integrate, differentiate is operational amplifiers. It is a linear device. The Summing Amplifier An OP-AMP to derived a single output voltage by summing multiple voltage inputs a summing amplifier is designed. Application of Electrical/ Electronic components in Microbial Fuel Cell (MFC) One of the limitations for application of MFC system is low voltage output. Apart from environmental and microbial parameters affecting performance of MFC, certain changes in electronic component may also help to improve voltage output where circuit designs can be modified (Meehan et al., 2011). Capacitors (Dewan et al., 2010), resistors, transistors, DC-DC converter are some electronic components which may help for electricity storage as well as boosting (Wang et al., 2015). By building large MFC, i.e. only increase in size will not improve power generation (Park and Ren, 2012). Modification in external resistance (R), known as load may also be helpful for higher electricity generation and greater COD (Chemical Oxygen Demand) reduction (Liu et. al., 2006). The current generated from MFC could be optimized and amplified with the help of Operational Amplifier (Walker, 1987). It can further be consumed by the Boost converter ((Park and Ren, 2012)) and Buck Boost converter. MFC with boost converter MFC could be connected as an input to boost converter and expected output from boost converter is 1.2 volt.MFC circuits can be integrated in series and parallel to achieve higher current and voltage output. As shown in below figure when MFC is connected in series, the resultant output should be summation of individual volt of MFC. In this Figure, four MFC could be connected in series which should produce approximately 2.4 V which is given to DC-DC converter for further boosting of voltage. Boost converter (DC-DC converter) with series connected MFC Conclusion A microbial fuel cell (MFC) is capable of powering an electronic device if we store the energy in anexternal storage device, such as a capacitor, and dispense that energy intermittently in bursts of high powerwhen needed. Therefore its performance needs to be evaluated using an energy-storing devicesuch as a capacitor which can be charged and discharged rather than other evaluation techniques, such ascontinuous energy dissipation through a resistor.Studied the basic to electronics to integrate with MFC to generate current, and further integrate it with electrical circuits to convert, amplify and stabilize the generated electricity into an electronic appliance usable format.