An 85-to-230VAC to 3.3-to-4.6VDc 1.52W Capacitor-Drop Sigma-Floating-SC AC-DC Converter with 81.3% Peak Efficiency

The internet-of-things (IoT) and smart home devices, such as smart power meters and smart remote control, have great demand for high-efficiency, low-cost and compact non-isolated AC-DC converter, which operates on the AC mains and delivers a battery-voltage output with a large voltage conversion ratio (VCR). These devices are becoming increasingly more intelligent and thus have higher power consumption. Traditional approaches involve inductive switching converter [1]–[4] and high-voltage linear regulator [5], [6], which lead to bulky volume or low efficiency. In contrast, fully integrated switched-capacitor (SC) topology [7] or SC-LDO hybrid topology [8] can achieve high power density. In addition, capacitive division [9]–[11] can convert high-voltage AC input to low-voltage AC, where the X-capacitor connected to the AC mains can block a large portion of the high voltage, then low voltage converters can easily handle the rest and be fabricated on chip. However, the output power of these capacitive converters is limited to $\mu\mathrm{w}$ levels, and the output cannot be adjusted due to the lack of regulation control. As shown in Fig. 9.1.1, to regulate the DC line $\mathrm{V}_{\text{REC}}$, the current adjustment method is achieved by a semi-active rectifier in [12], [13], and by a three-mode active rectifier in [14], superseding the passive rectifier. As an AC voltage source with $\mathrm{C}_{\mathrm{x}}$ can be regarded as an AC current source, prior works operate in two phases: 1) the $\mathrm{C}_{\text{REC}}$ charging phase and 2) the current freewheeling phase where the rectifier yields no output current. $\text{ln}[14],\mathrm{C}_{1}$ and $\mathrm{C}_{2}$ are added in series with $\mathrm{C}_{\mathrm{x}}$ to increase the loop impedance of the current freewheeling phase, thereby reducing the idle current. Although the current adjustment method can help regulating $\mathrm{V}_{\text{REC}}$, it inevitably leads to considerable constant current loss.