Study on Switching Power Converter Seeking to Omit Filter Capacitor

Because of the output voltage fluctuation caused by the sudden change of load, when the fluctuation lasts longer than the switching cycle, it can be adjusted to a certain extent through feedback. The LC filter circuit plays a decisive role in the effect of this voltage adjustment. In order to achieve the purpose of voltage adjustment, it is necessary to increase the switching frequency, reduce the values ​​of L and C, and extend the cutoff frequency of the filter to the high-frequency end as much as possible. At this time, it is possible to consider using two asymmetric inverters (with transformers) to output a two-phase square wave. The output voltage of each inverter is connected to a common load through half-wave rectification to extend the cutoff frequency to the high-frequency end.

The switching frequency is determined by the switching time of the MOSFET. In order to increase the switching frequency beyond its limit, a multi-phase switching method can be used to equivalently increase the switching frequency. However, the number of phases is also limited. In addition, the reason for the change is only on the load side, so it is also very effective to keep the cut-off frequency as low as possible. To achieve this goal, the use of electrical double-layer capacitor filters may be the future development direction. Of course, for this purpose, it is necessary to consider how to simultaneously reduce the equivalent series resistance and equivalent series inductance of the double-layer capacitor.