6. High Frequency Switching

The meaning of the term high frequency switching as related to a synchronous buck converter applications depends on the power range, the step in the voltage conversion and the switching performance of MOSFETs used as power switches. In a power range of 1 W, and low input voltages, a switching frequency up to 10 MHz can be reasonably achieved. In contrast, switching 20 A from V_in of 12 V down to 1.2 V at a frequency of 2 MHz is a big hurdle if an efficiency close to 90% is expected. Switching power loss increases with output current and input voltage level, and is proportional to switching frequency. Respectively, novel, fast switching MOSFETs have to be used. On the other hand, 2 MHz frequency means a period of 500 ns only. If a duty cycle of 10% is required, the whole on-cycle has to be accomplished within 50 ns. This requires very effective and fast gate voltage control.