A Dual-Input Bidirectional 3-Level Battery Charger with Coarse-Fine V_CF Balancing and Wide VCR for Foldable Mobile Applications

The on-going trends for foldable mobile phones require smaller form factors and high-density battery charging with a wide-input range to reduce the battery charging time. Thus, multi-level or hybrid converters can be a solution to reduce the size of passive devices and to achieve a higher efficiency at high input voltages compared with 2-L converters [1]–[4]. Another trend for mobile applications is wireless power sharing, which allows one mobile device to charge another device (e.g., smart watch, phone, or earbuds). If a travel adapter (T.A) is attached to the mobile device, wireless power sharing can allow two devices to be charged at the same time. To support this feature, the dual-input bi-directional 3-level charger is proposed as shown in Fig. 21.2.1 (top left). The dual-input SWs (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{CHG}}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$D_{\text{wc}}$</tex>) support wired and wireless battery charging, respectively, while the USB on-the-go <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(0.\mathrm{T}.\mathrm{G})$</tex> and wireless power sharing are connected to each switch. Figure 21.2.1 (top right) presents the proposed bi-directional charger operations. When the power sharing is activated with a load current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(/_{\text{TX}})$</tex> during battery charging, the adapter increases the charging current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(l_{\text{CHG}})$</tex> to supply power to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{wc}}$</tex> while simultaneously charging the battery. As the wireless device requires more current from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\prime_{\text{TX}}, /\text{cHG}$</tex> increases until it reaches an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$/\text{cHG}$</tex> regulation level. Then, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l_{\text{DHC}}$</tex> regulation current dominates while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1_{\text{BAT}}$</tex> decreases. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\vert \mathrm{f}l_{\text{TX}}$</tex> further increases to a heavy load, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text{DHG}}$</tex> is no longer sufficient to provide both <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\prime_{\text{TX}}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1_{\text{BAT}}$</tex> and as a result the battery begins to supply the insufficient current to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{wc}}$</tex>, At this point, the inductor current <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(I_{\text{ND}})$</tex> flows from the battery to the input, where the charger operates as the boost converter because the battery becomes a supplier. When the adapter is detached, the charger supplies power from the battery while regulating the bypass voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(V_{\text{BYP}})$</tex>. In a prior work [5], a bidirectional 3-L charger was presented. However, it does not support a seamless mode transition between the buck and reverse boost operations.