Linear mode power supplies and switch mode power supplies

Question

Question 1)a) Derive expressions for average output voltage, maximum and minimum inductor current, while a DC-DC buck converter is supplying a resistive load in continuous conduction mode. Estimate the change in output voltage if the non-ideal switch and diode are considered.

b) A buck converter has an input voltage that varies between 50V and 60V and a load that varies between 75W and 125W. The output voltage is 20V. For a switching frequency of 20 kHz, determine the minimum inductance to provide for continuous current for every operating possibility.

c) Distinguish between the linear mode power supplies and switch mode power supplies.

Question 2)a) Develop a suitable expression for output voltage of a boost converter if the inductor current has continuous and discontinuous modes. Draw the inductor voltage and current waveforms for both the modes.

b) The boost converter has the following parameters: V_s=20V, D=0.6, R=12.5Ω, L=65μH, C=200μF and f_s=40 kHz. Determine the output voltage, maximum and minimum inductor current and the output voltage ripple.

c) Make a comparison of performance/features of the buck, boost and cuk dc-dc converter topologies.

Question 3) Describe with appropriate circuit schematic the working principle of flyback converter supplying a resistive load. Draw the waveforms inductor voltage and current with the flux in the core.

b) The forward converter has the following parameters: V_s=48V, R= 10Ω, L_x= 0.4mH, C=100μF, f=35 kHz, N1/N2=1.5, N1/N3=1 and V_o=12V. Determine duty ratio, maximum and minimum currents in L_x and output voltage ripple. Verify that the magnetizing current is reset to zero during each switching period.

c) Discuss the benefits of high frequency transformers in power electronic applications.