1. (a) For the circuit shown in FIGURE 1 sketch the voltage waveform across the secondary winding of the transformer. On the same diagram sketch the load voltage waveform. The sketches should take into account diode voltage drops. Indicate the following on the sketches:
(i) when diodes are conducting and in what order
(ii) when the capacitor is charging and discharging
(b) With the aid of the above voltage waveform sketches, briefly explain the operation of the circuit.
Fig. 1
2. The source voltage for the power supply circuit shown in FIGURE 1 is mains, i.e. 230 V rms at a frequency of 50 Hz.
(a) Calculate the following for a load resistance of 25 ? and a smoothing capacitance of 1000 µF:
(i) rms and peak voltage across the secondary winding of the transformer
(ii) the peak voltage across the capacitor
(iii) the peak-to-peak and rms ripple voltages
(iv) the load d.c. voltage and current.
(b) Model the power supply circuit using PSPICE and use the simulation to plot the load and ripple voltages, the current in the capacitor and a diode. Compare the waveforms with the values calculated above and attempt to account for any discrepancies.
3. Briefly explain the function and operation of TR1, TR2, R1 and R1 in the circuit shown in FIGURE 2.
Fig. 2
4. List three advantages and three disadvantages of a switched-mode d.c. power supply (with primary switching) when compared with a linear regulated d.c. power supply.
5. Design, giving the necessary ratings and characteristics necessary for the transformer, bridge rectifier, reservoir capacitor and regulator, a 12 V, 2 A regulated power supply. Also identify any heat sink requirements.
The available mains supply is 230 V ±10% @ 50 Hz.