Size Reduction Techniques for AC-DC Converters

AC-DC converters allow electronic devices that operate with low DC voltage to utilize the reliable and ubiquitous high voltage AC mains as their power supply. Small-sized converters are preferred by customers because of their portability, compatibility, and space-saving features. However, conventional converters use many discrete components, which occupy a large area of the printed circuit board (PCB). Additionally, several large components, such as capacitors and transformers, also lead to bulky size. Recently, many scholars focus on increasing the switching frequency of the converters to reduce the size of transformers or inductors [1–5]. However, the increase in switching frequency is limited to the efficiency requirement and the switching component’s performance.

To further reduce the size, we investigated three strategies: (1) IC (integrated circuit) Implementations; (2) Active Capacitors; (3) Voltage-Drop Rectifiers. In this design, we applied a flyback converter structure to explore the IC Implementations and Active Capacitors methods. Furthermore, we searched for opportunities to replace the transformer with smaller voltage-drop rectifiers. An additional requirement is that the output voltage ripple ratio needs to be smaller than 2% to maintain the performance of the load device.

First, IC Implementation Technique is investigated to merge as many discrete components as possible. This strategy is estimated to save 10% of the space of the whole flyback converter with a 1.57% ripple ratio. Next, to further reduce the size, we need to shrink the size of the bulky components. One method to achieve that is replacing one of the big components with small elements. In this design, the large output capacitor is replaced with an active capacitor, and the total volume is expected to be reduced from 22.4 cm3 to 10.41 cm3 and the ripple ratio is around 1.87%. Finally, we explored voltage-drop rectifiers to find opportunities to remove the transformer of the flyback converter. We found that one kind of voltage-drop rectifiers, the capacitor-fed rectifier, occupies only approximately 40% of the normal transformer’s original physical size. A DC-DC converter is implemented after the capacitor-fed rectifier to suppress the output voltage ripple. Overall, these methods are effective to shrink the volume while maintaining the output voltage ripple small.