BTEC NC - Electronics - Function and Operation of Diodes, Transistors and Logic Gates

8/2/2019 BTEC NC - Electronics - Function and Operation of Diodes, Transistors and Logic Gates

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Brendan Burr BTEC National Certificate in ElectronicsFunction & Operation of Diodes, Transistors & Logic Gates

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Task 1

1.1a) Signal Diode b) Zener

Diode

1.2a) Half wave rectifier

b) Diodes act like non-return valves, allowing the current to flow in one direction but not theother, the direction is shown by the symbols arrow-head.Diode D1 will only allow the current to flow in the direction shown (i.e.from anode to cathode). D1 will be forward biased during eachpositive half cycle (relative to common) and will effectively behave

like a closed switch.When the circuit current tries to flow in the opposite direction, thevoltage bias across the diode will be reversed, causing the diode toact like an open switch.This is shown on the graph below, where the Live is able to getthrough on the positive half cycle, however when the waveform triesto go into the negative scale of the graph, it cannot get through dueto the diode, causing a gap in the waveform.

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1.3a)

b) Thediode is in place to prevent the current heading through R1 and downto 0V. The currents only path is then to the base and the collector ofthe transistor, therefore opening the transistor accordingly tostabilise the voltage.The current is looped through R2 to go through the diode if there areany variations in the flow, the transistor can open and close to enablea steady flow of current. This can then be used to protect circuitsfrom power surges.The zener diode is used so that if there is excess voltage then it willbreak down allowing the current to flow to 0 volts and not allow

damage to the components.

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N - Channel P - Channel


Task 2

2.1a) NPN Transistor

b) PNP Transistor -

c) Field Effect Transistor

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2.2a)

When there is no A.C. input the output is at 9V. This is because thevoltage travels through the RL resistor and cannot travel through thetransistor.There is also current supplied to the base of the transistor, this opens

the transistor when the current is large enough.When there is an A.C. input the transistor opens and the 9V are ableto go through the transistor and to 0V. The transistor opens becauseof the added current flow from the A.C. input.RB = Base Resistor : it limits the amount of current to the base of thetransistor.RL = Collector Resistor : it limits the amount of current to the collectorof the transistor.

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b)

The switch on the left of the circuit diagram supplies the base of thetransistor with 5V, when on.If the switch was off, or open, then the output voltage would bereading 9V. If the switch was on, or closed, then the output voltagewould be reading close to 0V.The waveform of the input is 180o phase inverted when it reaches the

output, so the positive section of the sinusoidal waveform becomesnegative and negative becomes positive.

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Task 3

3.1a) a . b + a + b = Qb) a . b = Q

c) = Q

3.2a) 2 Input NAND Gate

b) 2 Input NOR Gate

c) 2 Input EX-NOR Gate

3.3a) 2 Input AND Gate

a b Q

0 0 0

0 1 0

1 0 0

1 1 1

b) 2 Input OR Gate

a b Q

0 0 0

0 1 1

1 0 1

1 1 1

c) 2 Input EX-OR Gate

a b Q

0 0 0

0 1 1

1 0 1

1 1 0

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Bibliography

Through guidance from my lecturer, the following websites and textbooks I was able to complete this assignment:

BooksBTEC National Engineering (Mike Tooley & Lloyd Dingle)ISBN: 978-0-7506-8521-4

Websiteswww.wikipedia.orgwww.kpsec.freeuk.com/index.htmwww.technologystudent.com/elec1/elecex.htm

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Documents

BTEC NC - Electronics - Function and Operation of Diodes, Transistors and Logic Gates