Definition
Switching frequency is the rate at which a switch-mode power supply's transistors turn on and off, typically tens of kilohertz to several megahertz. It is one of the most consequential numbers a power-supply designer chooses, because nearly every other component sizing and loss term keys off it. Understanding the trade-off it controls explains why two supplies of the same wattage can differ enormously in size, weight, heat, and efficiency.
The fundamental trade-off
Raising the switching frequency lets the magnetics and filter capacitors shrink, because each component needs to store energy for a shorter interval. That is the main lever for boosting power density, and magnetics plus heatsinks can occupy more than 80% of a supply's volume. But higher frequency also increases switching loss in the transistors, raises core and winding losses in the magnetics, and intensifies electromagnetic interference (EMI) from faster edges. Push too far with the wrong devices and efficiency collapses.
How designers win on both fronts
The way out of the bind is better switches and better timing: wide-bandgap devices switch faster with less loss, and soft-switching topologies remove most per-transition loss so frequency can climb without overheating. This is why modern high-density supplies combine high switching frequency with resonant conversion and GaN or SiC transistors.
The two enablers of high switching frequency are detailed in our entries on soft switching (ZVS/ZCS) and gallium nitride (GaN) devices.
In Simple Terms
Switching frequency is the rate at which a switch-mode power supply’s transistors turn on and off, typically tens of kilohertz to several megahertz. It is…