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

摘要

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 $3imes mathrm{R}_{mathrm{DCR}, mathrm{BAT}}$ (-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.