electronics “the science that deals with the control of electrons in an electrical circuit or...

Electronics

“the science that deals with the control of electrons in an electrical circuit or system”

Electronics around us

Key words: energy conversions /transformations, input devices,microphone, solar cell, thermocoupleBy the end of this lesson you will be able to:

Describe the energy transformations involved in

the following devices: microphone,thermocouple, solar cell.State that the resistance of a thermistorusually decreases with increasing temperature,

and the resistance of an LDR decreases withincreasing light intensity.Carry out calculations involving V=IR for the

thermistor and LDR.

Electronic Systems

A useful system can change one thing

into another.

Put a coin in and you get a can of drink out.

The iron changes electricity to heat.

In electronics we think about the process as a “black box”

We use a block diagram to represent the system.

The Black Box

The Toaster as an electronic system

Radio Receiver

Electronic Thermometer

All electronic systems need electricalsignals to work.

At the input stage we need to convert aform of energy into an electrical signal.

At the output stage we need to convertthe electrical signal into another form of

energy.

Battery operated torch

Microphone

converts sound energy into electrical energy

Amplifier

amplifies the weak electrical signal

Loudspeaker

converts electrical energy into sound energy

Digital and Analogue Signals

There are two types of signals

used by electronic systems:

analogue and digital.

A digital signal..

…can have only 2 values, 1 or 0

1

0

An analogue signal...

…can have any value

Analogue Signals

Continuous range of values

Digital Signals

Only two possible values

Maximum (logic ‘1’ or high)

Minimum (logic ‘0’ or low)

Digital vs Analogue

Digital signals carry more information per

second than analogue signals.

Digital signals maintain their quality over

distance far better than analogue signals.

Input Devices

An input device converts

some form of energy into an

electrical signal.

The microphone as an input device

Microphone

What is the energy change which takes place in a microphone?

The microphone converts sound energy into an electrical signal.

Everyday uses of microphones?

Thermocouple

What is the energy change which takes

place in the thermocouple?

The thermocouple converts heat energy

into an electrical signal.

Thermocouple

The sensitivity of the thermocouple

is 40 µV / °C.

For every degree above roomtemperature the voltmeter readingincreases by

0.00004 V

Thermocouple

The hotter the temperature the higher

the reading on the voltmeter.

The colder the temperature the lower the

reading on the voltmeter.

Thermocouple

The largest voltage reached was

mV.

To convert to V we divide by 1000:

Thermocouple

=0.00004

volts in voltmeter from Reading

Added to room temperature of 23 °C means the highest temperature is

The Solar Cell

A solar cell convertslight (solar) energy into

an electrical signal.

The Solar Cell

As brighter lightshines on the solarcell, what happens to

the voltage output?

SolarCell

Voltmeter

Light Dependent Resistor

Light Up Resistance

Down

We find that increasing light intensity causes an LDR’s resistance to decrease.

Thermistor

Temperature Up Resistance Down

We find that heating a thermistor causes its resistance to decrease.

Ohm’s Law

I

V

R

Review

Ohm’s Law calculations involving LDRs and

Thermistors.

Input devices questions.

What have I learned today?

Key words: energy conversions / transformations,output devices, light emitting diodes (LED)

By the end of this lesson you will be able to:

Give examples of output devices and the energyconversions involved.Draw and identify the symbol for an LED.State that an LED will light only if connected one

way round. Describe by means of a diagram acircuit which will allow an LED to light.Calculate the value of the series resistor for anLED and explain the need for this resistor.

Output Devices

The electric motor converts electrical

energy into

kinetic energy

Output Devices

The relay switch is a magnetically

operated switch.

The Relay Switch

Explain the purpose of a relay switch:

The relay switch is a switch operated by

an electromagnet. It allows switching of a

circuit with a high current by closing a

switch in a circuit with a low current.

The Relay Switch

Explain how the relay works:

When the switch in the circuit with the lowvoltage supply is closed, the current through

the coil of wire creates a magnetic field. This

closes the switch contact in the secondcircuit, completing the second circuit andallowing the motor to operate.

Crocodile Physics [relay model] Virtual Int 2 Physics -> Electricity and Electronics -> Electronic Components -> Output Devices

The Light Emitting Diode (LED)

The LED is an output device which

changes electrical energy into

light

DON’T CONFUSE IT WITH AN LDR!

LED

A filament lamp and an LED are normally used for different purposes.

Where might an LED be used?

LED

What are the differences between the lamp and the LED?

The LED does not light if the connections to the d.c. power supply are reversed. It requires only a small current to operate. It is a digital output device i.e. on or off.

What are the advantages of the LED over a filament lamp?

The LED requires only a small current to operate. It does not get hot in operation.

Using a resistor in series with an LED

Why is it necessary to use a resistor inseries with an LED?

The resistor is required to limit the

current to avoid destroying the junction

of the LED.

Will this LED light?

YES!

It doesn’t matter where the resistor is!

But…will this LED light?

NO!It doesn’t matter where the resistor is…

but if the LED is “facing the wrong way” it will not light!

Connecting an LED

An LED will work only is connected to the

power supply the right way round.

In a circuit diagram, the arrow of the

diode must be pointing towards thenegative connection of the battery.

What about…this LED?


Oops – you’ve blown it up!

Series Resistor and LEDs

Virtual Int 2 Physics -> Electricity &

Electronics -> Electronic Components ->

Series Resistor for an LED

Calculating value of series resistor required -

exampleThe maximum voltage across an LED is 2.3 V. The current through it must notexceed 10 mA. The LED is connected to a 5 V supply. Calculate the value of the resistor R, connected in series with the

LED.

What about…this LED?

Since the LED and resistor are in series, what

can we say about the voltage?

VS = VLED + VR

and the current?

the current through each component is thesame (10 mA = 0.010 A)

Since the LED and resistor are in series, what

can we say about the voltage?

VS = VLED + VR

and the current?


supply voltage voltage across the resistor

voltage across the LED

Ω==

=

=

===

+=

270 0.01

2.7 R

R x 0.010 2.7

IR V

V 2.7 2.3– 5 V– V V

sideeach from V must take weV find To V V V

R

LEDSR

LEDRRLEDS

Calculating value of series resistor required -

exampleThe maximum voltage across an LED is 2 V. The current through it must notexceed 10 mA. The LED is connected to a 9 V supply. Calculate the value of the resistor R, connected in series with the

LED.

Since LED and resistor in series, what can

we say about the voltage?

VS = VLED + VR

and the current?


Ω==

=

=

===

+=

700 0.01

7 R

R x 0.010 7

IR V

V 7 2– 9 V– V V

V V V

R

LEDSR

RLEDS

7-Segment Displays

LEDs are commonly used in a 7-segment

display.

gf

de c

a

b

Tasks

Numerical Questions 74 – 79

Numerical Questions 80 - 83

Can you?

Name some input devices?

State the energy changes in input devices?

State the energy changes in output devices?

Describe where output devices might be used?

Describe applications of input devices?

Key words: NPN transistor, MOSFET transistor


Draw and identify the circuit symbol for anchannel enhancement MOSFET.Draw and identify the circuit symbol for an NPN

transistor.State that a transistor can be used as a switch

which is ON or OFF.Explain the operation of a simple transistorswitching circuit.

NPN Transistors

base

Collector

Emitter

NPN transistor

The transistor is made from p- and n- type semiconductor materials sandwiched together – n-type, p-type and n-type.

Current arises from the movement of electrons and vacancies called holes.

It is also possible to make a pnp transistor.

Transistors

base

Collector

Emitter

NPN transistor

The transistor can be used as an electronic switch with no moving parts.

It is either conducting or non conducting i.e. on or off.

Digital or analogue?

Transistors

base

Collector

Emitter

NPN transistor

The transistor is a digital process device.

When the switch is ON, current flows from the emitter to the collector.

How do we turn the switch on?

base

Collector

Emitter

NPN transistor

Whether the switch is on or off depends on the voltage across the base and emitter.

When the base-emitter voltage is less than 0.7 V then no current can flow and the switch is off.

base

Collector

Emitter

NPN transistor

When the base-emitter voltage reaches 0.7 V the switch is on and current flows from the emitter to the collector.

The transistor is a voltage controlled switch.

Metal Oxide Semiconductor Field Effect Transistor

(MOSFET)The transistor is also made from p- and n- type semiconductor materials.

We will use only one type of MOSFET.

MOSFET

gate

source

drain

MOSFET

The transistor can be used as an electronic switch with no moving parts.

It is either conducting or non conducting i.e. on or off.

Digital or analogue?MOSFET

gate

source

drain

MOSFET

The MOSFET is a digital process device.

When the switch is ON, current flows from the source to the drain.

MOSFET

gate

source

drain

How do we turn the switch on?

Whether the switch is on or off depends on the voltage across the gate.

When the voltage applied to the gate is less than 1.8 V then no current can flow and the switch is off.

gate

source

drain

What are the advantages of a transistor as a switch?FastCheapReliableNo mechanical parts – don’t wear out

The drawback is that the transitor can be

affected by temperature.

Light Controlled Circuits

This diagram shows a complete electronic circuit.

What is the input?

The process device?

The output?

Light Controlled CircuitsInput – a voltage

divider circuit.

The voltage across the resistor provides the

input to the transistor.


The transistor is the process device.


The LED is the output device.

How it works in the dark:

As light falls, the resistance of the LDR will

increase

therefore the voltage across the LDR will

The input voltage to the transistor thereforeRemember LURD - light up resistance down, so as light goes down resistance goes up



increase


increase

The input voltage to the transistor thereforeRemember the greater the resistance, the greater the share of the voltage. The LDR gets a greater share leaving less across the resistor.



increase


increase

The input voltage to the transistor therefore

decreaseRemember the voltage across the resistor provides the input to the transistor.

When the voltage is below

0.7 V

the transistor

switches OFF

and the LED

switches off

Remember 0.7 V across the base-emitter is the switching voltage for the npn transistor

At 0.7 V and above the npn transistor is ON. Below 0.7V the npn transistor is OFF.

The transistor is acting as a switch.

How it works as light level increases:

As light increases, the resistance of the LDR will

decrease


decrease


increases

Remember light up resistance down.

Remember the smaller the resistance, the smaller the share of the voltage. The LDR gets a smaller share leaving more across the resistor.

Remember the voltage across the resistor provides the input to the transistor.

When the voltage is above

0.7 V

the transistor

switches ON

and the LED

switches ON

Remember 0.7 V across the base-emitter is the switching voltage for the npn transistor

At 0.7 V and above the npn transistor is ON. Below 0.7V the npn transistor is OFF. The transistor is

acting as a switch.

This circuit switches ON as light levels increase.

How should the components be positioned to give a circuit which switches on as light levels decrease?

Another Light Controlled Circuit

Change positions of LDR and Resistor

- light level decreases- LDR resistance ………….- voltage across LDR …………….- transistor switch ……………- the LED is now …………..

increasesincreases

ONON

Another Light Controlled Circuit

Explain which circuit would be suitable for use in automatic street lights:

The second circuit in which the LED switches on as light decreases. As darkness falls, this could be used to switch on street lights automatically.

Making use of transistors

V

This diagram shows a complete electronic circuit.

Input – a voltage divider circuit.

The voltage across the thermistor provides

the input to the transistor.

The transistor is the process device.

The LED is the output device.

V

How it works –

As the temperature of the thermistor decreases the resistance of the thermistor will

increase

therefore the voltage across the thermistor

increases


increases

Remember temperature up resistance down, so as temperature goes down resistance goes up

Remember the greater the resistance, the greater the share of the voltage

Remember the voltage across the thermistor provides the input to the transistor.

V

When this voltage reaches

0.7 V

the transistor

switches ON

and the LED

lightsRemember 0.7 V across the base-emitter is the switching voltage for the npn transistor

At 0.7 V and above the npn transistor is ON

The transistor is acting as a switch.

V

This circuit acts as a temperature controlled circuit.

It switches on when the temperature is LOW.

V

How will this circuit behave?

This will act as a temperature controlled circuit which will switch on when temperature rises.

V

Suggest a possible use for this alternative version of the temperature-controlled circuit

This type of circuit might be used in a fridge – to warn when the temperature rises.

Another temperature controlled circuit

thermistor

mains 230 V

Heatingelement

relay switch Describe the operation of this circuit.

Why is it necessary to use a relay switch to operate the heater?

Key words: amplifier, gain


Identify, from a list, devices in which amplifiers

play an important partState that the output signal of an audio amplifier

has the same frequency as, but a larger amplitudethan, the input signal.Carry out calculations involving input voltage,output voltage, and voltage gain of an amplifier.

What is an amplifier?

An analogue process device. It is used

to make electrical signals bigger.

Amplifier – Physics Animations – Sound –

Amplifying Sound

Amplifier Input and Output

Amplifier

Input signal

Output signal

What effect does the amplifier have on the amplitude of the signal?What effect does the amplifier have on the frequency of the signal?

Voltage Gain

The amount of amplification of aparticular amplifier is described by itsgain.

What is meant by an amplifier with a gainof 500?

The output signal is 500 x the amplitudeof the input signal.

Voltage Gain

If an amplifier has a gain of 500, what

can you say about the frequency of the

input signal and the output signal?

Voltage Gain

To find the voltage gain of an amplifier

we use

voltage gain =

gain =

output voltage

input voltage

Vo

Vi

Units?

Voltage Gain: Example

The input voltage is 0.1 V and the output is 1.5 V. What

is the amplifier’s gain?

gain =

gain =

= 15

Vo

Vi

Units?

1.5

0.1

Power Gain of Amplifiers

You can also consider the power gain of an

amplifier.

Power gain =

output power

input power

Units?

Equations for Power

Power can be calculated using equations

which you have come across before.

VIP =

RIP 2=R

VP

2

=

Power Gain: Example

A girl connects a set of headphones ofresistance 16 Ω to her MP3 player. Theamplifier in the player produces 0.04 W ofpower.

What is the voltage applied to the headphones?

Calculate the input power to the amplifier when

power gain is 20.

Solution

VV

xV

VR

R

V

R

VP

8.0

64.01604.0

04.0

04.0

2

2

2

2

===

=

=

=

Solution

mWWxinput

input

xinput

input

input

outputgain

20102

20

04.0

04.020

04.020

3 ==

=

=

=

=

−

electronics “the science that deals with the control of electrons in an electrical circuit or...

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