BTEC NC - Analogue Electronics - Operation of IC Devices in Analogue Circuits

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Brendan Burr BTEC National Certificate in ElectronicsOperation of IC Devices in Analogue Circuits

Task 1

1.1 Obtain manufacturers data sheets for the following integrated circuits:

(a) Timer IC.

Attached

(b) Operational Amplifier IC.

Attached

(c) Linear Voltage Regulator IC.

Attached

1.2 For each of the above integrated circuits, identify the IC number.

Timer IC LM555CMOperational Amplifier IC LM124Linear Voltage Regulator IC LM125

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1.3 Briefly describe the operation of each device.

LM555CM (Timer IC)The LM555CM IC Chip is a highly stable device which can be used forgenerating accurate time delays or oscillation.

In a timing scenario for a Monostable circuit the time period can beeasily controlled by the pairing of a resistor and a capacitor. For anastable circuit the use of two resistors and one capacitor can be used.The LC555Cm IC Chip can be used for multiple applications in anumber of circuits, for example:

Precision TimingPulse GenerationSequential TimingTime Delay GenerationPulse Width ModulationPulse Position ModulationLinear Ramp Generator

Below is a top down view of the interior of the LC555CM IC Chip.

The Voltage supply (+Vcc) goes to pin 8 with 0V (Ground) connected toPin 1. The Trigger (Pin 2) starts the timing IC by providing a pulse.Depending on the time interval of the chip (Determined by t=RC1.1 for

a Monostable circuit) will vary the output, it will give an output voltagelevel for that time period of the +Vcc Supply Voltage.The timing interval can be interrupted by using the reset at pin 4. Atpin 5 there is access to the internal Potential divider.The threshold determines when the timing interval is complete.The Discharge (Pin 7) is connected to a capacitor, this will alsodetermine the time interval.

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LM124 (Operational Amplifier IC)The LM124 IC Chip contains four Operational Amplifiers which aredesigned to specifically work from one power source over a wide rangeof voltages. This eliminates the need of dual power supplies.The Op Amp can be used in many applications such as:

Non-Inverting DC GainDC Summing AmplifierPower AmplifierLED DriverBi-Quad RC Active Bandpass FilterFixed Current SourcesLamp DriverCurrent MonitorPulse GeneratorSquare wave OscillatorDriving TTLVoltage FollowerHigh Compliance Current SinkLow Drift Peak DetectorComparator with Hysteresis

Below is a top down view of the interior of the LM124 IC Chip.

There is a voltage supply to Pin 4 and Pin 11 is connected to 0V(Ground).Pins 3, 5, 10 and 12 are all the Non Inverting Inputs.Pins 2, 6, 9 and 13 are all the Inverting Inputs.Pins 1, 7, 8 and 14 are all the Outputs of the Op Amp.

The Op Amp is used to give a gain in voltage from its inputs and is oneof the most widely used electronic devices.

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LM125 (Linear Voltage Regulator IC)The LM125 IC Chip is used for providing positive and negative outputvoltages which are at currents of up to 100mA.It has a standby current drain of 3mA and the current limit is externallyadjustable.

The LM125 IC Chip can be used in many applications such as:2 Amp Boosted Regulator with Current LimiterPositive Current Dependant Simultaneous Current LimitingBoosted Regulator with Foldback Current LimitElectric Shutdown Circuit

Below is an interior schematic diagram view of the LM125 IC Chip.

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1.4 Describe two system applications for each device and produce thecircuit diagram of the application in each case.

LM555CM (Timer IC)Monostable Operation

The Monostable circuit is designed to give a single pulse at the Output.It is called a monostable as it is only stable in one state, which is whenthe Output is Low. When the Output is High it is only temporary.

The length of the pulse is called the Time Period and is determined bythe Capacitor (C) and the Resistor (Ra), as shown in the followingequation:

T=1.1 x Ra x C1The longest reliable time period is around 10 minutes anything longerand the calculation becomes unreliable.

The timing period begins when the Trigger (Pin2) is supplied with avoltage less than 1/3 that of the supply voltage. Once this hashappened the Capacitor (C) begins to charge through the Resistor(Ra). Through the time it takes for the capacitor to fully charge, theOutput state will remain high.During the charging of the capacitor all other trigger pulses will beignored.The threshold monitors the voltage across the charging capacitor,when this reaches 2/3 of the voltage supply the time period finishes

and the Output returns to Low.

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The Discharge (Pin 7) then connects to 0V and in turn discharges thecapacitor to ready it for the next cycle.

By connecting the reset to a push button and down to 0V all otherinputs can be cancelled by closing the connection on the push button.

This will make the output return to the low state immediately and willdischarge the capacitor.

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Astable Operation

The Astable circuit is designed to give continuous clock pulses, oncetriggered (Pin 2).

The Capacitor (C) is charged through the two series resistors (Ra) and(Rb).Once the voltage across the Capacitor reaches 2/3 that of the SupplyVoltage, the Output returns to a Low State.The Capacitor will discharge through the Resistor (Rb) as theDischarge (Pin 7) has now switched to 0V.The voltage across the Capacitor will soon reach 1/3 that of the SupplyVoltage again, removing the Discharge (Pin 7) from 0V and beginscharging the Capacitor until it reaches 2/3 of the Supply Voltage.The cycle will continue until the reset is connected to 0V.

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LM124 (Operational Amplifier IC)Single Op-Amp Bandpass Filter

The bandpass filter is designed to allow certain frequencies throughand block frequencies that are out of the bandpass range.

The range of frequencies that are allowed through is called thePassband, it is determined by the Upper and Lower limits.The Upper and Lower limits are not evenly spaced against the CentreFrequency, however if they were plotted in Log Graph paper theywould be.To work out the Centre Frequency the following equation should beused:

Centre Frequency = Square Root of the (Lower Frequency * UpperFrequency)

The Filter Bandwidth (BW) is the difference between the Upper andLower Limits.The Quality Factor (Q) is determined by the Centre Frequency dividedby the Filter Bandwidth.

For a single Op-Amp Bandpass Filter with both of the capacitors at thesame value, the Quality Factor has to be greater than the Square Rootof half of the Gain. This means that a Gain of 98 for example, wouldneed a Quality Factor of 7 or more.

The Diagram shows a 1.7 KHz bandpass filter with a Quality Factor of8 and a gain of 65 at 1.7 KHz.The capacitors have to be thesame value, therefore 0.01uF isused for both as it is a commonvalue in audio frequency circuits.

The Resistor values are workedout using the following threeformulas:

R1 = Q / (G*C*2*Pi*F)R2 = Q / (((2*Q^2)-G)*C*2*Pi*F)R3 = (Q*2) / (C*2*Pi*F)

R1 = 8 / (65*0.00000001*2*Pi*1700)R1 = 1152.252982 or 1K1

R2 = 8 / (((2*8^2)-65)*0.00000001*2*Pi*1700)R2 = 1188.832441 or 1K2

R3 = (8*2) / (0.00000001*2*Pi*1700)

R3 = 149792.8876 or 150K

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Low Power Op-Amp (50mW Audio Amplifier)

In the circuit below there is a small 8 ohm speaker which represents amicrophone. This is coupled to the Operational Amplifier Input througha 0.01uF Capacitor.

The speaker will pick up low frequencies easily and the small valuecapacitor attenuates the lower tones and helps to produce a betteroverall response. By varying this capacitor results in differences inresponse of different speakers.

The voltage gain of the Op-Amp determined by the feedback resistorwhich is around 1K on the below diagram.

The non inverting input (Pin 3) has around half of the voltage supply,this gives Pin 3 around 4.5V.

Because both of the inputs are equal, when the Op-Amp is operatingwithin is Linear Range, the voltage at Pin 2 (the Inverting Input) and theemitter of the transistor will also be 4.5V. At the emitter the voltage willchange by around 2V whenever the input is changed by around 2mV.

The output speaker power is about R * I^2 = 8 * 0.06^2 = 0.0288 or28.8mW.

The 100 Resistor and the 47uF Capacitor helps to prevent oscillation.There is also a 22uF Capacitor which helps to further stabilise the

operation of the device at the non-inverting input.

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ADP1720 (Linear Voltage Regulator IC)10A Regulator with Foldback Current Limiting

T

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Positive Current Dependent Simultaneous Current Limiting

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Bibliography

http://ludens.cl/Electron/solarreg/Solarr~1.htmhttp://en.wikipedia.org/wiki/DC_to_DC_converterhttp://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm

http://www.national.com/mpf/LM/LM555.htmlhttp://www.national.com/mpf/LM/LM124.htmlhttp://www.analog.com/en/power-management/linear-regulators/ADP1720/products/product.html

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http://ludens.cl/Electron/solarreg/Solarr~1.htmhttp://en.wikipedia.org/wiki/DC_to_DC_converterhttp://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htmhttp://www.national.com/mpf/LM/LM555.htmlhttp://www.national.com/mpf/LM/LM124.htmlhttp://www.analog.com/en/power-management/linear-regulators/ADP1720/products/product.htmlhttp://www.analog.com/en/power-management/linear-regulators/ADP1720/products/product.htmlhttp://ludens.cl/Electron/solarreg/Solarr~1.htmhttp://en.wikipedia.org/wiki/DC_to_DC_converterhttp://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htmhttp://www.national.com/mpf/LM/LM555.htmlhttp://www.national.com/mpf/LM/LM124.htmlhttp://www.analog.com/en/power-management/linear-regulators/ADP1720/products/product.htmlhttp://www.analog.com/en/power-management/linear-regulators/ADP1720/products/product.html

Documents

BTEC NC - Analogue Electronics - Operation of IC Devices in Analogue Circuits