Voltage Regulator Design Exercise and Simulation in Multisim

The Circuit

This exercise assignment requires you to analyse the design of a type of voltage regulator, simulate its performance in Multisim, calculate some component values and answer a number of questions.

The use of Multisim was covered in the module’s practical sessions (weeks 3-5) and all information about how to use the software is still available on the Canvas site.

You should submit your answers type-written on paper, along with printed screens  of the Multisim circuit and screen snippets of the meter and oscilloscope readings obtained during simulation.

Figure 1 below shows a type of voltage regulator circuit, in the dashed box. It takes an 18 V average DC input voltage and regulates it to provide 10 V DC to a 20 W load. All component types and values are labelled, and you should use these to construct the circuit in Multisim.

(i) shows the block diagram of a mains operated DC power supply. Explain the function of each subsystem, sketch the time dependent voltage waveforms at points A, B, C, D and E.

(ii) What is the name of the circuit?

(iii) What components in the circuit determine the value of the output voltage applied to the load?

(iv) Given that the zener diode voltage is nominally 5.6 V, calculate the ideal values for R₁ and R₂. Explain all steps in your calculations and justify the choice of any unspecified parameters.

(v) Given the results of these calculations, explain the justification for the resistor values given.

(vi) Tables and show extracts from the datasheets for the two transistors specified. Identify the two most important ratings to be considered in the design of this circuit and explain the justification for choosing each of these transistors for this design.

(i) Construct the circuit of Figure 1 in Multisim and include a prinscreen of the circuit with your submission.

(ii) Add three multimeters connected to measure the following; the load voltage, the load current, and the current through the chain of resistors R₁ and R₂.

(iii) Run the simulation and record all of the voltage and current values obtained.

(iv) Comment on the values recorded by explaining whether they are as expected and, if not, what the possible reasons could be.

(v) Replace the DC source in Figure 1 with an AC voltage source. The Multisim symbol for this is shown in Figure 3. Edit the AC source parameters to give 1 V pk, 18 V voltage offset and 100 Hz.

Include a printout of the revised circuit with your submission.

(vi) Connect an oscilloscope to measure, on channel A, the output from this AC source and run the simulation. Provide a snippet image of the oscilloscope screen and comment on what the result shows.

(vii) Re-connect the oscilloscope to measure, on channel A, the signal across the load. Provide a snippet image of the oscilloscope screen and comment on what the result shows.

(viii) Increase the level of peak voltage on the AC source until you can observe ripple on the load voltage. Record the peak AC voltage and provide a snippet image of the oscilloscope screen showing the resulting signal across the load.

(ix) What do you conclude about the performance of this circuit as a voltage regulator?