A 96.8%-Efficiency Continuous Input/Output-Current Step-Up/Down Converter Powering Disposable IoTs with Reconfigurable Multi-Cell-Balanced Alkaline Batteries

Abstract

As internet-of-things (IoT) devices continue to be installed everywhere, the concept of disposable IoT is emerging owing to better cost-efficiency and ease of maintenance without battery recharging. Lasting several years, IoTs powered with standard alkaline batteries can be a promising solution due to the long shelf life, low cost, and high reliability of these batteries as compared to the Li-ion type. As shown in the top portion of Fig. 11.8.1, a single alkaline cell has a maximum voltage of 1.5V, but it can decay down to 0.9V [1]. To power an IoT device operating with mathrm{V} {mathrm{DD}}=2mathrm{V}, a variety of design options can be considered, such as the battery configuration and the power conversion topology, as shown in Fig. 11.8.1 (bottom). The first approach is step-down conversion [2], [3] from multi-cell batteries (3×BATs) connected in series. In this configuration, cell-balancing must be carefully considered; otherwise, the energy of the BATs cannot be fully utilized if any weak cells exist among them. Considering the power conversion stage, the input RMS current mathrm{I} {mathrm{IN},mathrm{RMS}} becomes much higher than the average current mathrm{I} {mathrm{IN},mathrm{AVG}} due to the inherently discontinuous mathrm{I} {mathrm{IN}} supplied from batteries, resulting in a significant power loss in the series combination of the direct current resistance (mathrm{R} {mathrm{DCR}, mathrm{BAT}}) of batteries which in the case of 3 batteries in series is 3times mathrm{R} {mathrm{DCR}, mathrm{BAT}} (-300m Omega). Regarding step-up conversion [4], [5] with parallel-connected batteries, most of the energy imbalances are compelled to be uselessly wasted via reverse currents mathrm{I} {mathrm{B}} ' The mathrm{I} {mathrm{B}} also can cause explosion or leakage of corrosive substances. Furthermore, the inductor current mathrm{I} {mathrm{L}} is likely to be high, caused by the discontinuous mathrm{I} {mathrm{D}} delivered to the output; this significantly contributes to the power loss with a large mathrm{R} {mathrm{DCR},mathrm{IND}} of the inductor. In summary, the battery cell imbalance and the discontinuous input/output (I/O) current of converter are perhaps the major issues that prevent the full utilization of alkaline batteries in IoT applications.