Refer to the given flyback converter circuit diagram If Vo i

Refer to the given flyback converter circuit diagram. If Vo is 5 V for a 5 ohm load resistor, Vin = 30 V , N1/N2 = 3 , the magnetizing inductance Lm1 = 500 uH, and switching frequency fs = 40kHz, calculate the duty ratio D, average Iin and Iout , and Iin(0) , Iin , Iout (0) , Iout as shown in the figure . Assume lossless conditions.

out in in Figure 1 (a) Flyback converter Iin(0) (b) its waveforms

Solution

fly back converter Input to the circuit may be unregulated dc voltage derived from the utility ac supply after rectification and some filtering. The ripple in dc voltage waveform is generally of low frequency and the overall ripple voltage waveform repeats at twice the ac mains frequency. Since the SMPS circuit is operated at much higher frequency (in the range of 100 kHz) the input voltage, in spite of being unregulated, may be considered to have a constant magnitude during any high frequency cycle. A fast switching device (‘S’), like a MOSFET, is used with fast dynamic control over switch duty ratio (ratio of ON time to switching time-period) to maintain the desired output voltage. The transformer,, is used for voltage isolation as well as for better matching between input and output voltage and current requirements. Primary and secondary windings of the transformer are wound to have good coupling so that they are linked by nearly same magnetic flux. As will be shown in the next section the primary and secondary windings of the fly-back transformer don’t carry current simultaneously and in this sense fly-back transformer works