Assignment title / DC Networks
Assessor / Paul Lewis
Date issued
Final deadline
Duration (approx) / 2 sessions (8 hours)
Qualification suite covered / BTEC Extended Diploma in Engineering Level 3
Units covered / A part of Unit 6 Electrical and Electronic Principles
Learning aims covered / Be able to use circuit theory to determine the current, voltage and resistance in direct current (DC) circuits
Scenario / You have been employed as a junior technician in a local electronics company who make power supplies. A new power supply has appeared on the market which used considerably less power that the one made by your company. You have been commisioned by your managing director to investigate the power drawn by your power supply circuits and suggest possible alternatives
Task 1 / Part a)
For the circuit shown below:

Choose 5 different value resistors from the following table for resistors R1 – R5
Calculate the total power dissipation of your circuit then choose a suitable voltage from the table below based on this value
Resistor values for R1 – R5 / Voltage values for V1
10 Ω / 3 volts
22 Ω / 5 volts
33 Ω / 6 volts
47 Ω / 9 volts
100 Ω / 10 volts
220 Ω / 12 volts
330 Ω / 15 volts
470 Ω / 24 volts
1k Ω
Calculate:
  • The total circuit resistance Rt
  • The total circuit current It
  • The current flowing through R3
  • The voltage dropped across R2
  • The power dissipated by R1
  • Confirm the results of your calculation using the laboratory simulator (Multisim)
Care should be taken by each student to ensure that where possible, the combination of components and supply voltage are unique for each assessment.
Part b)
Check your calculations for P1 by constructing the circuit on breadboard and carefully measuring the values of resistance, current and voltage as specified. Make a table similar to the one shown below and enter your values.
Parameter / Calculated values / Measured values / Simulated values
Total circuit resistance
Total circuit
current
Current flowing through R3
Voltage dropped across R2
Power dissipated in R1
Part c)
Use DC circuit measurements to calculate the internal resistance of a battery
  • Measure the offload voltage of a given battery using a multimeter
  • Measure the onload voltage of the battery when connected to the virtual cat circuit using a multimeter
  • Measure the current drawn by the virtual cat circuit using a multimeter
  • Use the data from the measurements to calculate the internal resistance of the battery
  • Include all of the above data in a technical report
Part d)
You are required to use test equipment to measure the forward and reverse characteristics of two semi-conductor diodes. You should use a 1N4001 diode and a zener diode to carry out this experiment.
Use the following circuit as a basis for this test:

  • Draw and label a diagram of the 1N4001 general purpose diode connected in forward bias and reverse bias mode
  • Measure the forward characteristic of the diode between 0.5 volts and 0.7 volts using steps of 0.01 of a volt by adjusting the resistance box R1
  • Measure and record the reverse characteristic of the diode using Multisim between 49.9 volts and 50.01 volts using steps of 0.01 of a volt
  • Carry out a similar experiment on a zener diode (of your choice) using its data sheet as a guide to the magnitude of voltages required to test its forward and reverse characteristics
  • Draw and label graphs of both data sets
  • Compare the two graphs showing the conduction characteristics of both diodes, consult the data sheets and evaluate your findings in terms of forward and reverse voltages, power dissipation and maximum operating current

Evidence you must produce for this task /
  • Formulae, calculations and solutions neatly presented
  • Photographic evidence showing the DC Network for both resistors, diodes and the internal resistance of a battery.
  • Photographic evidence of all readings taken by the multimeter
  • Readings taken for the forward and reverse current and voltages through and across both diodes to be neatly tabulated
  • Graphs to be drawn to show the conduction characteristic of both diodes in both forward and reverse bias modes
  • Your evidence should be presented in the form of a report which contains and introduction to each task and a written conclusion

Criteria covered by Task 1:
To achieve the criteria you must show that you are able to: / Unit / Criterion reference
Use DC circuit theory to calculate current, voltage and resistance in DC Networks / 6 / P1
Use a multi-meter to carry out circuit measurements in a DC circuit / 6 / P2
Compare the forward and reverse characteristics of two different semi-conductor diodes / 6 / P3
Task 2 / For the circuit shown below:
Use the same table as for Unit 6 P1 in order to choose component values.
Circuit 2

  • From the attached table choose different values for R1 – R3
  • From the attached table choose different voltages for V1 –V2
  • Use Kirchoff’s laws to determine the current flowing through R1, R2 and R3
  • Determine the power dissipation in R1
Use Multisim to confirm the results of your calculations and attach to the assignment as a screen dump
Evidence you must produce for this task / Formulae, calculations and solutions neatly presented
A screen dump from a simulation showing the current through R1 and the voltage across R1.
Criteria covered by Task 2:
To achieve the criteria you must show that you are able to: / Unit / Criterion reference
Use Kirchoff’s laws to determine the current in various parts of a network having four nodes and the power dissipated in a load resistor containing two voltages sources / 6 / M1
Task 3 / The circuit shown below is a simple voltage regulated power supply:

Investigate the function and operation of the circuit and choose components to produce an output voltage with the following specification:
  • Output voltage = 5 volts
  • Output current up to a maximum of 100 mA
  • Ripple voltage <10mV
The values can have a tolerance of +/- 5%
  • Simulate the circuit to prove its operation
  • Explain how and why the value for each component was chosen
  • Build and test the final solution and evaluate its performance against the given specification

Evidence you must produce for this task / Formulae, calculations and solutions neatly presented
Photographic or video evidence of the circuit with readings showing that the circuit is performing to specification
A simulation proving that the components chosen allow the circuit to perform within the specified parameters
Criteria covered by Task 2:
To achieve the criteria you must show that you are able to: / Unit / Criterion reference
Analyse the operation and the effects of varying component parameters of a power supply circuit that includes a transformer, diodes and capacitors / 6 / D1
Sources of information / Websites

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