Choosing the best operating frequency for your power supply is a complex trade-off that includes size, efficiency, and cost. Generally speaking, low-frequency designs tend to be the most efficient, but they are also the largest and most expensive. While increasing the frequency reduces size and cost, it increases circuit losses. Next, we describe these trade-offs using a simple buck power supply.

We start with the filter component. These components occupy the majority of the power supply volume, and the size of the filter is inversely proportional to the operating frequency. On the other hand, every switching transition is accompanied by energy loss; the higher the operating frequency, the higher the switching losses and the lower the efficiency. Second, higher frequency operation usually means that smaller component values can be used. Therefore, higher frequency operation can bring significant cost savings.

Shown is the relationship between frequency and volume of a buck power supply. At a frequency of 100 kHz, the inductor occupies the majority of the power supply volume (dark blue area). If we assume that the volume of an inductor is related to its energy, then its volume decreases in direct proportion to frequency. Since the core loss of the inductor will greatly increase at a certain frequency and limit further size reduction, the above assumption is not optimistic in this case. If the design uses ceramic capacitors, the output capacitor volume (brown area) shrinks with frequency, which means less capacitance is required. On the other hand, the input capacitor is typically chosen because of its ripple current rating. This rating does not change significantly with frequency, so its volume (yellow area) tends to remain constant. Additionally, the semiconductor portion of the power supply does not vary with frequency. Thus, passive components occupy the majority of the power supply volume due to low-frequency switching. As we move to high operating frequencies, the semiconductor (i.e. semiconductor volume, light blue area) starts to occupy a larger proportion of the space PWM.