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

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 VDD=2V, 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 IIN,RMS becomes much higher than the average current IIN,AVG due to the inherently discontinuous IIN supplied from batteries, resulting in a significant power loss in the series combination of the direct current resistance (RDCR, BAT) of batteries which in the case of 3 batteries in series is 3×RDCR, BAT (-300m Ω). Regarding step-up conversion [4], [5] with parallel-connected batteries, most of the energy imbalances are compelled to be uselessly wasted via reverse currents IB ` The IB also can cause explosion or leakage of corrosive substances. Furthermore, the inductor current IL is likely to be high, caused by the discontinuous ID delivered to the output; this significantly contributes to the power loss with a large RDCR,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.