Novel Upper Capacitor for Half-Bridge Switching Converter Topologies that Reduces EMI and Capacitor Ripple Current

Electromagnetic interference (EMI) and power density are two highly studied fields as power converters become smaller and more numerous. Physical EMI filters can improve EMI performance at the cost of size. Passive components (inductors, capacitors) are often the limiting factor for improving power density. This digest presents a simple modification to the typical half-bridge converter that results in improved EMI performance and decreased required capacitance. The modification comes in the form of a single capacitance placed between the input and output nodes of the converter. This capacitor allows for the ripple currents at both nodes to be shared. As there is an element of correlation between these ripple currents, any differential mode currents can be canceled through this capacitance. This results in improved EMI performance and decreased total capacitor ripple current when compared with a typical half-bridge converter when the total capacitance (and therefore the required physical size of the capacitors) between the two converters is held constant. Furthermore, the reduction in total capacitor ripple current can allow for a decrease in capacitor size if capacitor ripple current drives capacitor sizing. Equations for capacitor current are derived and optimum capacitance ratios are found mathematically. Improvements over the typical half-bridge converter are demonstrated through both simulation and physical experiments. Experimental capacitor current measurements alongside input and output FFTs are provided.