Switching Losses and Conduction Loss

We see that the fundamental properties and behavior of an inductor, as described in Chapter 1, are ultimately responsible for the significant V-I overlap during crossover. 

The same situation is present in the case of any switching topology. Therefore, the switching loss equation presented earlier also applies to all topologies. What we have to remember is, that in our equations, we are referring to the voltage across the switch (when it is OFF), and the current through it (when it is ON). In an actual converter, we will need to ultimately relate these V and I to the actual input/output rails and load current of the application. The procedure for that is described later. 

However, unlike the crossover loss, the conduction loss is not frequency-dependent. It does depend on duty-cycle, but not on frequency. For example, suppose the duty cycle is 0.6 then in a measurement interval of say, one second, the net time spent by the switch in the ON-state is equal to 0.6 seconds. But we know that conduction loss is incurred only when the switch is ON. So in this case, it is equal to a x 0.6, where a is an arbitrary proportionality constant. Now suppose the frequency is doubled. Then the net time spent in 

We can pose a rather philosophical question — why is it that the switching loss is frequency-dependent, but not the conduction loss That is simply because the conduction loss coincides with the interval in which power is being processed in the converter. Therefore, as long as the application conditions do not change (duty cycle fixed, input and output power fixed), neither can the conduction loss. 

The equation to calculate the conduction loss of a mosfet is simply 

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