Rares Bodnar

A 250W/30A fast charger for ultracapacitors with direct mains connection

This paper presents a fast and compact charger architecture for ultracapacitors with direct connection to 230V AC mains supply. The charger delivers a DC output current which allows compensation for inductive and other non-ideal behaviour in the EDLC at medium and high frequencies. The internal converter uses self oscillating control circuits which provide a variable switching frequency over a broad range. This allows the circuit to adapt to the variation of the output voltage (0–16.2V) and fluctuations of the mains network, thereby minimizing losses over the whole operating envelope.

An integrated ultracapacitor fast mains charger with combined power/current optimisation

This paper presents a novel integrated self-oscillating step-down converter for the fast charging of stacks of large ultracapacitors from a 230V AC mains source. The charger architecture controls both power and current to optimise the charge rate with respect to the limitations imposed by the mains source and the capacitors themselves. The circuit has been fabricated in a 0.35μm bulk medium voltage CMOS, process.

High-Accuracy Current Memory in HV CMOS Technology

This brief describes an improved current memory circuit aimed at circumventing problems inherent in using a high-voltage double-diffused MOS (DMOS) with CMOS technology. In addition to dealing with the excessive output conductance of a simple cell with cascoding in the familiar way, the circuit addresses the significant drain-gate feedthrough seen in such technologies. A replica bias scheme ensures that the gm of the memory device remains substantially constant notwithstanding the signal current level variations, leading to improved control over charge injection errors. The topology may also be used in conventional small geometry CMOS technology.

22.1 A self-tuning resonant inductive link transmit driver using quadrature-symmetric phase-switched fractional capacitance

Inductive coupling for power transfer is increasingly popular in many applications such as RFID and wireless charging. While much recent work has focussed on receivers [1,2], less consideration has been given to the transmit function. High-Q antenna circuits are beneficial for several reasons. Activation of a link at a distance requires a large magnetic field from the transmitter, so for a given antenna current, lower driver voltages may be used, simplifying the driver and its power supplies, and improving overall efficiency. Further, the inherent filtering allows a high-efficiency switching driver to be used while reducing harmonics in the current. However, the consequent narrow bandwidth requires precise tuning to resonance. The excitation frequency may be varied in some applications, but this transfers the tuning problem to the receiver. Any transmit tuning circuitry must be linear with large voltages (from a few V to kV) and currents (mA to many A). A conventional technique is to use multiple external capacitors selected by large switches [3] or even relays. The number of selectable elements needed depends on the Q factor, component tolerances, and environmental effects, with a typical system requiring 5 or more extra capacitors and associated HV switches (Fig. 22.1.1), plus extra IC pins, adding to system cost and volume.

Adaptive Tuning of Large-Signal Resonant Circuits Using Phase-Switched Fractional Capacitance

Inductively coupled systems used in applications such as RFID and wireless power often require high

A CMOS MF energy harvesting and data demodulator receiver for wide area low duty cycle applications with 230 mV start-up voltage

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Continuous tuning of inductive link antennae with zero voltage switched fractional capacitance

factor resonant transmitters to maximize the magnetic field and achieve high overall efficiency. However, these are sensitive to environmental detuning as well as component tolerances. Existing methods for accurate tuning require search algorithms, usually requiring the suspension of normal operation in order to calibrate the resonant inductor–capacitor circuit, thus reducing power throughput and increasing system complexity. We describe here how zero-voltage switched fractional capacitance techniques may be used to achieve continuous and real-time adaptive tuning of large-signal resonant inductor–capacitor circuits. Minimal additional circuitry is required and tuning is maintained without disrupting normal operation. Many variants are possible for the implementation of the system, and some tradeoffs relating to the available tuning range and operating voltages are analyzed for two alternative topologies. Experimental results are presented for a 125-kHz demonstration system.

A Self-Tuning Resonant-Inductive-Link Transmit Driver Using Quadrature Symmetric Delay Trimmable Phase-Switched Fractional Capacitance

A low voltage start-up energy harvesting medium frequency (MF) receiver is presented, for use as the power and synchronisation part of a remote sensor node in a wide area industrial or agricultural application. Low operational duty cycle is possible with an embedded low speed data channel, leading to low start-up and operating voltage taking priority over power efficiency. The receiver consists of a rectifier, a power management unit and a phase-shift keying (PSK) demodulator. The proposed rectifier can cold start from 250mV antenna input and deliver 900mV DC output with 24% power conversion efficiency. The measurements demonstrate the QPSK demodulator consuming 1.27μW with a supply voltage of 630mV at a data rate of 1.6kbps with 1MHz carrier frequency. The rectifier is implemented in a standard threshold 0.18μm CMOS technology, occupies 0.54mm2 and can deliver 10.3μW at 3V to an external battery or capacitor.

A CMOS MF energy harvesting and data demodulator receiver for wide area low duty cycle applications with 250 mV start-up voltage

Driver circuits for inductively coupled systems such as wireless charging and RFID are more efficient if a high Q factor can be achieved but this requires tuning to compensate for component tolerances and environmental influences. Any tuning system used must be able to handle potentially large voltages at resonance as well as achieving precise tuning. In this paper, we describe the use of a low loss fractional capacitance tuning based on synchronous switching at zero voltage instants, which has the advantages of continuous adjustment and low component and pin count overhead for the controller circuitry. Methods for generating suitable timing signals are presented and the practical trade-offs between tuning range and switch breakdown voltage are analysed. Results are compared with theory for a 125kHz antenna system, as typically used for wireless charging or automotive immobiliser applications.