the wires or PCB traces, as well as in the switches and inductor, as in any electrical circuit. Dynamic power losses occur as a result of switching, such as the charging and discharging of the switch gate, and are proportional to the switching frequency. It is useful to begin by calculating the duty cycle for a non-ideal buck converter, which is: where: Vsw is the voltage drop on the power switch, is the voltage drop on the synchronous switch or diode, and VL is the voltage drop on the inductor. The voltage drops described above are all static power losses which are dependent primarily on DC current, and can therefore be easily calculated. For a diode drop, Vsw and may already be known, based on the properties of the selected device. where: Ron is the ON-resistance of each switch, and RDC is the DC resistance of the inductor. The duty cycle equation is somewhat recursive. A rough analysis can be made by first calculating the values Vsw and using the ideal duty cycle equation. For a MOSFET voltage drop, a common approximation is to use RDSon from the MOSFET's datasheet in Ohm's Law, V = IDSRDSon(sat). This approximation is acceptable because the MOSFET is in the linear state, with a relatively constant drain-source resistance. This approximation is only valid at relatively low VDS values. For more accurate calculations, MOSFET datasheets contain graphs on the VDS and IDS relationship at multiple VGS values. Observe VDS at the VGS and IDS which most closely match what is expected in the buck converter. In addition, power loss occurs as a result of leakage currents. This power loss is simply where: Ileakage is the leakage current of the switch, and V is the voltage across the switch. Dynamic power losses are due to the switching behavior of the selected pass devices (MOSFETs, power transistors, IGBTs, etc.). These losses include turn-on and turn-off switching losses and switch transition losses. Switch turn-on and turn-off losses are easily lumped together as where: V is the voltage across the switch while the switch is off, trise and tfall are the switch rise and fall times, and T is the switching period but this does not take into account the parasitic capacitance of the MOSFET which makes the Miller plate. Then, the switch losses will be more like: When a MOSFET is used for the lower switch, additional losses