A non isolated (transformerless) topology of the buck-boost converteris shown in Fig.l.a. The converter consists of dc input voltage source VS, controlled switch S, inductor L, diode D, filter capacitor C, and load resistance R. With the switch on, the inductor current increases while the diode is maintained off. When the switch is turned off, the diode provides a path for the inductor current. Note the polarity of the diode that resuts in its current being drawn from the output. The buck-boost converterwaveforms are shown in Fig.l.b. The condition of a zero volt-second product for the inductor in steady state yields V.DT=-V(-D)T-----() Hence, the dc voltage transfer function of the buck-boost converter is, M =V,/V,=-D/(1-D)-----(2) The output voltage Vo is negative with respect to the ground. Its magnitude can be either greater or smaller (equal at D=0.5) than the input voltage as the name of the converter implies. When switch S is ON: When switched on ON for a time tv the diode will be open circuited since it does not allow currents in reverse direction from input to output Hence the Buck Boost converter can be redrawn as follows During this state the inductor charges and the inductor current increases. The current through the inductor is given as