11/6/2023 0 Comments Peak flux density![]() ![]() 1: Typical specific power loss curves for different switching frequencies and flux densities Pv = specific power loss (kW/m 3 ) and can be estimated from core manufacturers data curves (such as the typical curve shown below in Fig. The following calculation illustrates the relationships. Why? Because core loss is proportional to volume but cooling is proportional to the core’s radiating surface area. Smaller cores can more easily tolerate a higher peak flux density at higher switching frequencies than larger cores. This relationship accounts for one of the primary motivations for moving to higher frequency designs they allow the use of smaller magnetic components. So the designer can reduce the core size or reduce the number of turns or proportionally reduce both. When you double the switching frequency in a design, you halve your flux density for a given number of turns in the transformer. In the latter case, wire size, path length and winding density all have a role to play. Transformer losses can be divided into core loss - the energy used in magnetizing the core, and the conduction loss associated with passing current through the windings of the transformer. In this article we will focus on the transformer effects of changes to switching frequency. The effects of switching frequency on power loss in a flyback converter can be assigned to basic two types: switching losses in the power MOSFET and losses in the core and windings of the power transformer. Switching frequency does affect power loss in a switching power supply. This article will explain why this assumption does not hold true and why engineers can even increase efficiency by moving to a higher frequency. They examined losses associated with different aspects of the design and showed that, in some cases, the widely-held assumption about high switching frequencies - the higher the switching frequency of a power supply, the lower its efficiency - is wrong. To prove this, engineers at Power Integrations tested comparable flyback designs running at 66 and 132 kHz. Power supply designers can increase efficiency while moving to a higher switching frequency. The effects of switching frequency on power loss in a flyback converter can be assigned switching losses in the power MOSFET and losses in the core and windings of the power transformer Switching frequency and efficiency: A complex relationship ![]()
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