SLUAAP2 March 2023 LMG2610 , UCC28782
Another aspect of power-dense designs that must be discussed is the switching frequency and the relation to the energy storage requirements of the system. This is what is commonly stated as increasing the switching frequency reduces the size of the power converter. Analyzed at a deeper level, the DC power delivered to a load is processed by a power converter which fundamentally works on the principle of storing energy from the input for some time and then releasing it to the load. The power that is delivered to the load is mandated by two factors: the amount of energy that can be stored then released every cycle, and the frequency at which the process happens.
As an analogy, suppose a large shipment of goods has to be made from one port to another across a body of water within a set amount of time. On one hand, consider a) a cargo ship that can deliver the goods in just a few trips. On the extreme contrary, consider b) a speed boat that can make multiple quick trips with less goods per trip. In this analogy, the goods on the vessel represent the energy stored, while the number of trips represent the switching frequency. In the end, both the cargo ship and the speed boat deliver the same amount of goods (energy) in the same amount of time, maintaining constant power. Although the net result of the delivery is the same, there are two differences in the two scenarios: a) transfers more stored energy at a slower frequency, and b) one transfers less stored energy at a higher frequency, or Equation 1.
In a power converter, this energy storage mechanism is carried out by the largest components, primarily the magnetics such as inductors and transformers. For magnetics, size is directly proportional to energy storage, while energy storage is directly proportional to inductance, or Equation 2.
Because of this relationship, small-form-factor designs must switch at high frequency to reduce the energy storage requirement, and as a result, reduce the overall size. As shown in Figure 1-1 the inductance (energy storage) requirement for a given power level is inversely proportional to the switching frequency. However, it is important to keep in mind that switching losses are incurred by increasing the switching frequency, and can become a thermal concern. Techniques on how to mitigate these losses are explained in the following sections.