Efficiency of switching regulator (ignoring overlapping switching losses)

By understanding the current D of the switch tube V and the freewheeling diode D (see Figures d and e), the loss and efficiency of the circuit can be calculated. If the conduction voltage drop is zero when the current flows through the switch tube V and the diode D, the total loss is zero and the efficiency is 100%. When V is turned off, the maximum voltage it withstands is Udc, but the current is zero, so the loss is zero; when V is turned on, the reverse voltage of D is Udc, but the current is extremely small, and the loss is also zero.

The efficiency of the switching regulator is shown in the figure

In this way, all the losses of the circuit are just the conduction losses of V and D plus the overlapping switching losses of V. At the moment V is turned on, the rising current and the falling voltage of V overlap, which will cause conduction losses. At the moment V is turned off, the falling current and the rising voltage overlap, which will cause turn-off losses.

As can be seen from Figures (d) and (e), during the conduction time of V and D (TON and Toff), the average current is the midpoint value of the slope, that is, the DC output current Io. Since the conduction voltage drop of V and D is 1V in a wide current range, the conduction loss can be expressed as

If overlapping switching losses are neglected, the efficiency is