High-efficiency high voltage hybrid charge pump design with an improved chip area

A hybrid charge pump was developed in a 0.13- $\mu \text{m}$ Bipolar-CMOS-DMOS (BCD) process which utilised high drain-source voltage MOS devices and low-voltage integrated metal-insulator-metal (MIM) capacitors. The design consisted of a zero-reversion loss cross-coupled stage and a new self-biased serial-parallel charge pump design. The latter has been shown to have an area reduction of 60% in comparison to a Schottky diode-based Dickson charge pump operating at the same frequency. Post-layout simulations were carried out which demonstrated a peak efficiency of 38% at the output voltage of 18.5 V; the maximum specified output voltage of 27 V was also achieved. A standalone serial-parallel charge pump was shown to have a better transient response and a flatter efficiency curve; these are preferable for time-sensitive applications with a requirement of a broader range of output currents. These findings have significant implications for reducing the total area of implantable high-voltage devices without sacrificing charge pump efficiency or maximum output voltage

Design & Evaluation of a Hybrid Switched Capacitor Circuit with Wide-Bandgap Devices for DC Grid Applications

ABSTRACT As technologies advance, the rate at which renewable power sources, such as solar photovoltaic (PV) and wind, are being added to the power grid is increasing. Typically, PV power plants require large inverters for direct current to alternating current (DC-AC) power conversion, as well as large transformers to step up voltages to the grid voltage. Offshore wind farms and large PV power plants in remote locations often aggregate power on a DC bus in order to improve efficiency and reduce the cost of power conversion hardware within the energy complex. However, the power must still be converted to AC for integration into the grid. Research is being done to allow greater adoption of low, medium, and high voltage DC distribution, wherein DC power is used directly by loads. This has the potential for additional cost savings. To better realize this vision, however, new DC-DC converter technologies must be developed that are small, cheap and efficient at the voltages and power levels relevant to grid integrations. This project demonstrates the feasibility of a switched capacitor boost converter topology that is scalable to 10 kilovolts, and can serve as an interface between lower voltage PV arrays and medium voltage DC (MVDC) distribution lines. In particular, this approach relies on switched capacitors, wide-bandgap (WGB) devices, and high-frequency switching to achieve high power density and high gain. As part of this work, two prototypes were constructed including a benchtop-scale prototype rated for 25W at 500 Volts and a 6 kW 10 kV converter. In particular, this second converter was demonstrated in hardware to deliver 2.56 kW at 10 kV DC to a resistive load with greater than 95% efficiency, demonstrating the feasibility of this converter for grid applications

Power management systems based on switched-capacitor DC-DC converter for low-power wearable applications

The highly efficient ultra-low-power management unit is essential in powering low-power wearable electronics. Such devices are powered by a single input source, either by a battery or with the help of a renewable energy source. Thus, there is a demand for an energy conversion unit, in this case, a DC-DC converter, which can perform either step-up or step-down conversions to provide the required voltage at the load. Energy scavenging with a boost converter is an intriguing choice since it removes the necessity of bulky batteries and considerably extends the battery life. Wearable devices are typically powered by a monolithic battery. The commonly available battery such as Alkaline or Lithium-ion, degrade over time due to their life spans as it is limited by the number of charge cycles- which depend highly on the environmental and loading condition. Thus, once it reaches the maximum number of life cycles, the battery needs to be replaced. The operation of the wearable devices is limited by usable duration, which depends on the energy density of the battery. Once the stored energy is depleted, the operation of wearable devices is also affected, and hence it needs to be recharged. The energy harvesters- which gather the available energy from the surroundings, however, have no limitation on operating life. The application can become battery-less given that harvestable energy is sufficiently powering the low-power devices. Although the energy harvester may not completely replace the battery source, it ensures the maximum duration of use and assists to become autonomous and self-sustain devices. The photovoltaic (PV) cell is a promising candidate as a hypothetical input supply source among the energy harvesters due to its smaller area and high power density over other harvesters. Solar energy use PV harvester can convert ambient light energy into electrical energy and keep it in the storage device. The harvested output of PV cannot directly connect to wearable loads for two main reasons. Depending on the incoming light, the harvested current result in varying open-circuit voltage. It requires the power management circuit to deal with unregulated input variation. Second, depending on the PV cell's material type and an effective area, the I-V characteristic's performance varies, resulting in a variation of the output power. There are several works of maximum power point tracking (MPPT) methods that allow the solar energy harvester to achieve optimal harvested power. Therefore, the harvested power depends on the size and usually small area cell is sufficient for micro-watt loads low-powered applications. The available harvested voltage, however, is generally very low-voltage range between 0.4-0.6 V. The voltage ratings of electronics in standard wearable applications operate in 1.8-3 V voltages as described in introduction’s application example section. It is higher than the supply source can offer. The overcome the mismatch voltage between source and supply circuit, a DC-DC boost converter is necessary. The switch-mode converters are favoured over the linear converters due to their highly efficient and small area overhead. The inductive converter in the switch-mode converter is common due to its high-efficiency performance. However, the integration of the inductor in the miniaturised integrated on-chip design tends to be bulky. Therefore, the switched-capacitor approach DC-DC converters will be explored in this research. In the switched-capacitor converter universe, there is plenty of work for single-output designs for various topologies. Most converters are reconfigurable to the different DC voltage levels apart from Dickson and cross-coupled charge pump topologies due to their boosting power stage architecture through a number of stages. However, existing multi-output converters are limited to the fixed gain ratio. This work explores the reconfigurable dual-output converter with adjustable gain to compromise the research gap. The thesis's primary focus is to present the inductor-less, switched-capacitor-based DC-DC converter power management system (PMS) supplied by a varying input of PV energy harvester input source. The PMS should deliver highly efficient regulated voltage conversion ratio (VCR) outputs to low-power wearable electronic devices that constitute multi-function building blocks