Topic 11Main contentsLast lecture review Principles of DC-AC converter
Main contents • Last lecture review • Principles of DC-AC converter Topic 11
1.4Problems10-1A 12-Vregulated linearpowersupplyof thetypeshown in Fig. 10-1a designed to operate with a 60-Hz acvoltage in range of 120V (+10%~-25%).At the maximumload, the peak-to-peak ripple in the capacitor voltage is 1.oVThe power supply is designed such that Vd.min-V。=0.5V inFig.10-1b.IoCalculate the loss of大3BaseErrotNefficiency due to powercontrolimpLine input0.or3-Vo,r60-HzlossesinthetransistorattransformerRectifierFiltercapacitor(a)full load, with the inputvoltage at its maximum.Ud(t)range(Hint: Approximate thecapacitorvoltagewaveformwithstraight-linesegments.)(b)Figure 10-1 Linear power supply: (a) schematic, (b) selection of transformer turns ratioso that Vd.min>V,bya small margin
3 10-1 A 12-V regulated linear power supply of the type shown in Fig. 10-1a designed to operate with a 60-Hz ac voltage in range of 120V (+10%~-25%). At the maximum load, the peak-to-peak ripple in the capacitor voltage is 1.0V. The power supply is designed such that Vd,min-Vo=0.5V in Fig.10-1b. Calculate the loss of efficiency due to power losses in the transistor at full load, with the input voltage at its maximum. (Hint: Approximate the capacitor voltage waveform with straight-line segments.) 1.4 Problems
10-2Aflybackconverterisoperatinginacompletedemagnetization mode. Derive the voltage transfer ratioV.N.in terms of the load resistance R, switching frequencyfs, transformer inductance Lm, and duty ratio D
4 10-2 A flyback converter is operating in a complete demagnetization mode. Derive the voltage transfer ratio Vo /Vd in terms of the load resistance R, switching frequency fs , transformer inductance Lm, and duty ratio D
Problem10-4Aflybackconverterisoperatinginanincompletedemagnetization mode with a duty ratio of 0.4. in the sameapplication, another option may be to parallel two half-sizeflyback converters as shown in Fig. 10-9b. Compare theripple in the input current ig and the output stage current i.waveforms in these two options, assuming a very largeoutput capacitor such that vo(t)=Vo.(a)(b)Figure 10-9 Other flyback topologies: (a) two-transistor flyback converter; (b) parallledflyback converters
5 10-4 A flyback converter is operating in an incomplete demagnetization mode with a duty ratio of 0.4. in the same application, another option may be to parallel two half-size flyback converters as shown in Fig. 10-9b. Compare the ripple in the input current id and the output stage current io waveforms in these two options, assuming a very large output capacitor such that vo (t)≈Vo . Problem
Problem10-5 A switch-mode power supply is to be designed with thefollowingspecifications:Va=48V±10%,V.=5V,f.=100kHzPjoad is 15~50W.A forward converter operating in acontinuous-conduction mode with a demagnetizing winding(N3=Ny) is chosen. Assume all components to be idealexcept the presence of transformer magnetizationinductance,VI(a) Calculate Na/N if this+NNIN,本Dturnsratio is desired to be asVasmall as possible(b) Calculate the minimumyalue of thefilterinductancePracticalforwardconverter5
inductance. + Vd - + Vo - 1 L iL + vL - D2 T N1N3 N2 i i i D2 1 3D3 Practical forward converter 5 (a) Calculate N2/N1 if this turns ratio is desired to be as small as possible. (b) Calculate the minimum value of the filter inductance. Problem 10-5 A switch-mode power supply is to be designed with the following specifications: Vd =48V±10%, Vo=5V, fs=100kHz, Pload is 15~50W. A forward converter operating in a continuous-conduction mode with a demagnetizing winding (N3=N1 ) is chosen. Assume all components to be ideal except the presence of transformer magnetization