Pulse-frequency modulation

There are practical difficulties in the design of electronics when working with non-fixed frequencies, such as transmission line effects in board layout and magnetic component selection, so generally, PWM mode is preferred.

When driving light loads, however, the effects of DC resistances are reduced and AC losses in the inductor, capacitor, and switching elements play a larger role in overall efficiency.

This is especially true in discontinuous mode operation, in which the inductor current drops below zero, resulting in the discharging of the output capacitor and even higher switching losses [de].

PFM mode operation allows the switching frequency to be reduced and for a control method that prevents the inductor current from dropping below zero during light loads.

All of this done at the expense of output voltage and current ripple, which increases as a result of the reduction in switching frequency and the gap between pulse trains.