Unit 39: Electronic Principles Unit Workbook 1 - … WorkBook 1 of 4 - HN... · Unit Workbook 1 – Level 5 EEE – U39 Electronic Principles – LO1 Semiconductor Testing author:

www.unicourse.org Unit Workbook 1 – Level 5 EEE – U39 Electronic Principles – LO1 Semiconductor Testing author: Michael Lopez BEng(Hons) MSc PGCert CertEd MIFL MIET FHEA ©UniCourse Ltd 2015

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online learning

Pearson BTEC Higher Nationals in Electrical and Electronic Engineering (QCF)

Unit 39: Electronic Principles

Unit Workbook 1 in a series of 4 for this unit

Learning Outcome:

Testing Procedures for Semiconductor

Devices and Circuits

http://www.unicourse.org/


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Contents INTRODUCTION .................................................................................................................................................. 3

GUIDANCE .......................................................................................................................................................... 3

1.1 Circuits and Testing ................................................................................................................................ 5

1.1.1 Half-Wave Rectifier ......................................................................................................................... 5

1.1.2 Full-Wave Rectifier .......................................................................................................................... 6

1.1.3 Zener Regulator .............................................................................................................................. 6

1.1.4 Transistor Switching Circuit ............................................................................................................ 8

1.1.5 Transistor Amplifier Circuit ............................................................................................................. 9

1.1.6 IC Voltage Regulator ..................................................................................................................... 10

1.1.7 Instruments ................................................................................................................................... 11

1.2 Devices ................................................................................................................................................. 12

1.3 Manufacturer Literature ...................................................................................................................... 14



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Purpose

Theory

Question

Example

INTRODUCTION This Workbook guides you through the learning outcomes related to:

Circuits and testing: half and full wave rectifying; zener regulator; switching and amplifier circuits for

transistors; IC voltage regulators instruments e.g. CRO, probes, signal generators, multi-meter, logic

Devices: semiconductor devices e.g. diodes (rectifier characteristics including forward/reverse bias modes,

zener, LED, photodiode, thyristor, triac), transistors (bipolar, unipolar and fieldeffect, including

characteristics and switch and amplifier modes), photo-transistors, optocouplers, integrated circuits (741

operational amplifier applications including filters, comparators, power supplies and oscillators), IC voltage

regulator, ‘specialist’ ICs (analogue and digital)

Literature: manufacturers’ specifications; manuals; characteristics; circuit diagrams and support (online

and offline)

GUIDANCE This document is prepared to break the unit material down into bite size chunks. You will see the learning

outcomes above treated in their own sections. Therein you will encounter the following structures;

Explains why you need to study the current section of material. Quite often learners

are put off by material which does not initially seem to be relevant to a topic or

profession. Once you understand the importance of new learning or theory you will

embrace the concepts more readily.

Conveys new material to you in a straightforward fashion. To support the treatments

in this section you are strongly advised to follow the given hyperlinks, which may be

useful documents or applications on the web.

The examples/worked examples are presented in a knowledge-building order. Make

sure you follow them all through. If you are feeling confident then you might like to

treat an example as a question, in which case cover it up and have a go yourself.

Many of the examples given resemble assignment questions which will come your

way, so follow them through diligently.

Questions should not be avoided if you are determined to learn. Please do take the

time to tackle each of the given questions, in the order in which they are presented.

The order is important, as further knowledge and confidence is built upon previous

knowledge and confidence. As an Online Learner it is important that the answers to

questions are immediately available to you. You will find the answers, upside down,

below each set of questions. Contact your Unit Tutor if you need help.



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Challenge

ee

Video

You can really cement your new knowledge by undertaking the challenges. A

challenge could be to download software and perform an exercise. An alternative

challenge might involve a practical activity or other form of research.

Videos on the web can be very useful supplements to your distance learning efforts.

Wherever an online video(s) will help you then it will be hyperlinked at the

appropriate point.



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1.1 Circuits and Testing

1.1.1 Half-Wave Rectifier The half-wave rectifier circuit is shown below.

An AC sinewave drives the primary of a transformer. On the secondary side there is a diode connected in

such a way that only when its anode is positive will it pass current through to the load resistor. The results

of a MicroCap Transient Analysis for this circuit are shown below.

The red plot is the AC sinewave input to the primary of the transformer. Notice that the period of this

sinewave is 1ms, therefore it is a 1kHz sinewave.

Notice that between 0 and 0.5ms the output is a virtual copy of the positive wave input. As soon as the

input starts going negative (at 0.5ms) then the diode becomes reverse biased and does not pass current to

the load resistor at all (apart from some minor leakage current). In this case the output is flat (virtually zero

volts). Once the input goes positive again (1ms) then the output responds positively also.

This circuit is available on Moodle for you to simulate in MicroCap



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1.1.2 Full-Wave Rectifier The half-wave rectifier circuit is shown below.

Here the secondary of the transformer is centre-tapped, with the centre-tap grounded. Any positive half

cycles present at the anode of D1 are passed to the load resistor. Any positive half cycles present at the

anode of D2 are also passed to the load resistor. The circuit has the effect of flipping the negative input half

cycles into positive half cycles at the output, as shown in the MicroCap Transient Analysis below.


1.1.3 Zener Regulator A Zener diode is always connected with the most positive voltage connected to the cathode (reverse

biased). When sufficient voltage is supplied to the Zener diode it will reach a point where the voltage can

increase virtually no more, but the current drawn can increase considerably.

Zener diodes must be wired into DC circuits. We must never apply AC to a Zener diode. The simple circuit

below illustrates how a Zener diode may be used to supply a fixed voltage from a DC source which has

some ripple (deviations in voltage)…



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The Zener diode use here is a 4.7V type. That means that the output voltage (OUT) should be a nice steady

4.7 volts regardless of any ripple in the input voltage (IN). To mimic an unwanted ripple voltage the circuit

has a sine source in series with the 12V battery. This sine source has a peak value of 0.5V and will be added

to the steady +12V, as shown in the MicroCap Transient Analysis below.

Here we see a ripple (blue) superimposed onto the 12V battery voltage. In red we see a nice steady 4.7V

DC voltage at the output. The purpose of the resistor is to absorb the voltage which the Zener diode

rejects. For example, if the ripple is +0.5V then the input voltage will be 12.5V in total. Since only 4.7V of

this will appear across the Zener diode then the remainder (7.8V) will appear across the resistor. We may

then work out the resistor current to be 7.8 1000 = 7.8𝑚𝐴⁄ . We need to ensure that such resistors are

capable of absorbing the power we supply to them. This one dissipates 𝑉𝑅𝐼𝑅 = 7.8 × 0.0078 = 60.8𝑚𝑊

whilst the Zener diode dissipates 𝑉𝑍𝐼𝑍 = 4.7 × 0.0078 = 36.7𝑚𝑊. When designing such circuits we must

ensure the power dissipation levels for all of our components are within the limits of our design.




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1.1.4 Transistor Switching Circuit Transistors may be used as switches or amplifiers. Here we shall look at transistors in a switching circuit. A

very basic but extremely useful transistor switching circuit is a NOT gate. A NOT gate is constructed below,

using CMOS transistors…

The PMOS transistor M1 will be become a virtual short circuit between its source and drain when a low

voltage (logic 0, zero volts) is applied to its gate. The NMOS transistor M2 will become a virtual short circuit

between its source and drain when a high voltage (logic 1, 5 volts) is applied to its gate. The effect of

connecting the transistors as shown is that when a logic 1 is applied to the input (IN) then M1 will be short

and M2 will be high impedance – that means that the output is high. When a logic 0 is applied to the input

then M2 will be short and M1 will be high impedance – that means that the output is low. We therefore

have an inverter.

The transistors here are switching very fast, as shown by the MicroCap Transient Analysis below…

The input here (blue) is a square wave with a 1ms period (i.e. 1kHz ). The output (red) is the inverse of the

input. This is a NOT gate. [Ignore the kinks in the output waveform – a result of the transistor models used]




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1.1.5 Transistor Amplifier Circuit Consider the common emitter amplifier below…

The transistor is biased by the resistor ladder comprising R3 and R4 and feedback for stability is provided

by R2. The voltage gain of the amplifier is roughly equal to R1/R2 = 4.7k/1.2k = 3.9. This is confirmed by

the MicroCap Transient Analysis below…

The voltage gain on these plots is (11.149 – 3.593)/2 = 3.8. This is in good agreement with our prediction.




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1.1.6 IC Voltage Regulator IC voltage regulators are used extensively in electronic circuits. Common output voltage values are 3.3V, 5V

and 12V. Let’s take a look at the LM117 adjustable IC regulator…

The input voltage can be up to 37V DC and the output voltage can be adjusted from 1.2V to almost 37V DC.

The actual voltage required is set by varying the potentiometer (R2) resistance. The output voltage is given

by the equation…

𝑉𝑂𝑈𝑇 = 1.25 (1 +𝑅2

𝑅1) + 𝐼𝐴𝐷𝐽𝑅2

The datasheet for this device gives the typical value of 𝐼𝐴𝐷𝐽 as 50µA. Therefore, if we wanted an output

voltage of 5V to power some TTL circuits then we need to transpose the above equation to find the value

of R2…

𝑅2 =𝑉𝑂𝑈𝑇 − 1.25

(1.25𝑅1 + 𝐼𝐴𝐷𝐽)

=5 − 1.25

(1.25240 ) + 50 × 10−6

= 713Ω

This value produces a 5V output. We confirm this by replacing the potentiometer with a 713Ω resistor and

performing a ‘Dynamic DC’ analysis in MicroCap…




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1.1.7 Instruments MicroCap gives full access to the following instruments…

Oscilloscope

Analogue Probe

Signal and function generators

Digital multimeters

Logic probe

Spectrum Analyser

Logic Analyser

Noise Analyser

You will gain plenty of practice in using these instruments throughout this unit and other units.



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1.2 Devices MicroCap is very versatile in allowing you to place a component on a schematic and plot its

characteristic(s). Just click on the ‘Plot’ button when the dialogue box is open for a component (if the

dialogue box is not open then double-click on the component to open it). This applies to…

General purpose diodes

Zener diodes

Bipolar Transistors

CMOS Transistors

Operational Amplifiers

A couple of examples, direct from MicroCap…

1N4148 Diode



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The forward-biased characteristic for the 1N4148 is shown below…

The reverse-biased characteristic for the 1N4148 is shown below…



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2N2222A Transistor

It is not too obvious how to copy these characteristics so just press ALT + PrtScn to put the plot on the

clipboard.

1.3 Manufacturer Literature There is a wealth of manufacturers’ literature online for all components you are ever likely to use. A Google

search quickly brings up many sources. Some examples…

http://www.onsemi.com/pub_link/Collateral/2N3903-D.PDF

http://www.ti.com/lit/ds/symlink/lm117.pdf


http://www.onsemi.com/pub_link/Collateral/2N3903-D.PDF

http://www.ti.com/lit/ds/symlink/lm117.pdf

Documents

Unit 39: Electronic Principles Unit Workbook 1 - … WorkBook 1 of 4 - HN... · Unit Workbook 1 – Level 5 EEE – U39 Electronic Principles – LO1 Semiconductor Testing author: