The previous chapter developed a fully integrated high-voltage switched-capacitor converter (SCC) with a DC input voltage. This chapter, along with the subsequent one, targets an AC input voltage, thereby unlocking additional applications powered by the ubiquitous AC mains. While facilitating an AC input voltage, the other specifications of Sect.
3.1 such as complete integration and high power density persist.
In prior fully integrated AC-DC converters, the AC-DC stage not only rectifies the AC input but also performs the down-conversion. They employ a capacitive divider, leveraging the suitability of capacitors for integration. However, the combination of the low AC mains frequency (50 or 60 Hz) and the low capacitance density on-chip results in a high input impedance. This high impedance prevents the flow of large currents, ultimately restricting the power density to values \({\leq }{1.6}\,\mu \mathrm {W/mm}^{2}\).
To overcome the dependence on the mains frequency, this chapter investigates a fully integrated DC-DC stage following the AC-DC stage to perform the down-conversion. The ability to independently set the switching frequency of the DC-DC converter, irrespective of the AC mains, enables higher power densities. This approach requires a DC-DC converter handling the slowly varying rectified AC input, spanning from 0 to 325 V (assuming the European mains). The DC-DC converter introduced in the previous chapter is incompatible with this input range due to its fixed ideal voltage conversion ratio (iVCR). In response, this chapter extends the high-voltage SCC from the preceding chapter into a multi-ratio (or gearbox) converter, as a first step toward AC-DC conversion.
The chapter starts by explaining why a wide-input-range DC-DC converter can handle a rectified AC input voltage. The following part shows that state-of-the-art fully integrated DC-DC converters cannot handle the input voltages required for the AC-DC application and delves into the specific challenges. To address these challenges, a high-voltage multi-ratio DC-DC topology is proposed. Subsequently, the implementation details are presented, covering the high-voltage driver design and high-voltage input sensing. Finally, this chapter shows the measurement results obtained from the prototype and compares them with state-of-the-art solutions.
