Buck type converter is a voltage-reducing converter that converts DC input voltage to other lower DC voltage. As shown in FIG. 2, this circuit comprises one active switch (MOSFET), a passive switch (diode), capacitor and inductor as its output filter.
Buck -DC Buck -Type Converter
For low working voltage, the passive switch (diode) is often replaced with active switch (MOSFET) so that the shrinkage of power on the switch can be reduced. When using 2 active switches, both of these switches will work alternately, and there is only one switch that closes at any time. The average value of the converter output voltage is proportional to the ratio between the switch closing time (the conduction switch / ON) to the switching period. Usually this power factor value is not smaller than 0.2, because if operated at a higher voltage ratios, the switch will work under its reliability and cause the down converter efficiency. For very high (Vd / Ed) ratios, typically used isolated DC-DC converters or topologies equipped with transformers.
The output current ripple analysis is required to design the filter or output filter of DC-DC converter . From the equation below, it is seen that to obtain the ripple current of the small buck converter , the inductor filter (L) is required , the value will decrease by increasing the switching frequency. The current output current of DC-DC converter will be maximum if the converter is working on the duty cycle (d) = 0.5
The below is a current condition that flows across the inductor filter when the DC-DC converter is working in critical condition. What is meant by the critical condition here is the condition where the current in the inductor flows to the load until it is precisely zero at the OFF switch, or the inductor works as current source. From the picture it is seen that the current flowing in the inductor is proportional to the value of the output current ripple. In this condition, the picture shows that the average ripple current rating is proportional to 1/2 of the peak-to-peak current ripple which can be calculated by the following equation: