Young-Jin Woo

A 40 mV Transformer-Reuse Self-Startup Boost Converter With MPPT Control for Thermoelectric Energy Harvesting

This paper presents transformer-based self-starting boost converter architecture with low-power maximum power point tracking (MPPT) control for low-voltage thermoelectric generator applications. The minimum working voltage of the proposed boost converter is 40 mV with oscillation through a positive feedback loop formed by a native MOS and transformer. The oscillation autonomously starts up by thermal noise and VOUT is charged up to 1.2 V by the oscillation so that the control block can operate. After that, the transformer for start-up is reused as an inductor, and the normal boost converter mode is enabled for better energy transfer efficiency. An improved MPPT sensing method is also proposed to simplify the circuit. The prototype chip is implemented in a 0.13-μm CMOS process. It operates with an input voltage range of 40 mV to 300 mV and provides a maximum output power of 2.7 mW with a maximum efficiency of 61% at an output voltage of 2 V.

Load-Independent Control of Switching DC-DC Converters with Freewheeling Current Feedback

In this paper, a load-independent converter with freewheeling current feedback, whose output is controlled by a comparator, is presented. This control method is very useful for single-inductor multiple-output (SIMO) converters. A single-inductor bipolar-output (SIBO) converter with the proposed control scheme is implemented in a 0.5 mum power BiCMOS process and uses 3.2 mm2 of die area. The current sensing gain can be increased and and the circuit is less sensitive to switching noise than CPM converters are because the slope compensation used in CPM converters reduces the current sensing gain to comply with low supply voltage.

Load-Independent Control of Switching DC-DC Converters With Freewheeling Current Feedback

A new control scheme of freewheeling current control is proposed for switching DC-DC converters. The output voltage is regulated by a comparator operation, and in the main current loop, the freewheeling current is feedback-controlled to a reference level in average. The converter control loop is no longer dependent on the values of the inductor, output capacitor, or the load equivalent resistance. The design of a loop compensator is therefore greatly simplified and the loop response can be very fast approaching that of a hysteresis converter. As an example, a single-inductor bipolar-output DC-DC converter with the proposed freewheeling current control is implemented in a 0.5 mum BiCMOS process. The converter has one positive output of 4 V and one negative output of -4.8 V. A maximum efficiency of 81% is achieved at a total output power of 250 mW with a switching frequency of 800 kHz.

Multiple-output step-up/down switching DC-DC converter with vestigial current control

A single-inductor dual-output boost converter reported in [1] works either in discontinuous conduction mode or in pseudo-continuous conduction mode and requires separate controllers. As each controller regulates the output in time-multiplexed manner, it is difficult to extend the number of outputs and power capacity. The converter reported in [2] solves these limitations by adopting comparator-controlled method. Each comparator-controlled output receives its required energy and one final PWM controller adjusts the total inductor current so that the remaining current is adequate for the last output. However, as the PWM controller regulates one of the converter outputs, the response of controller becomes slow and voltage ripple of the other outputs increases when the load current of PWM-controlled output is reduced to zero (or near zero). As a possible solution, minimum bleeding current can be set for the last output, however, this approach degrades the efficiency at light-load condition. Also, the operation region of the previously reported multiple-output converters is restricted to step-up mode only.

A Synchronous Multioutput Step-Up/Down DC–DC Converter With Return Current Control

This brief presents a new return-current control method for a multioutput step-up/down dc-dc converter. Compared with prior multioutput dc-dc converters, the presently described converter can generate outputs higher or lower than the input voltage with simple control-loop compensation while guaranteeing stability in a wide load range. Using a 0.5-mum bipolar CMOS (BiCMOS) process, a converter having five outputs has been implemented for an LG active-matrix organic light-emitting diode (AM-OLED) display panel. The implemented converter operates at 1-MHz switching frequency with 4.7- muH inductor and 10-muF capacitor. Experimental results show that the proposed control method can generate tightly regulated stepped-up or -down outputs stably under a wide load variation. The conversion efficiency is higher than 80% at a typical AM-OLED panel grey level.

Analog-digital switching mixed mode low ripple-high efficiency Li-ion battery charger

This paper describes a low noise and high efficiency analog-digital switching mixed mode battery charger for production facilities of Li-ion batteries. The requirements for battery chargers for production facilities are very strict. The accuracy of output voltage and output current should be below 0.1% with very low ripple current. Therefore analog type linear regulators are widely used for a battery charger in spite of their inefficiency and bulkiness. We combined a linear regulator as a voltage source with digital switching converter as a dependent current source. Low current ripple and high accuracy are obtained by a linear regulator while high efficiency is achieved by digital switching converter. Experimental results show that the proposed method has 0.1% ripple and 90% efficiency at an output current of 1 A for a battery voltage of 4 V.

One-Chip Class-E Inverter Controller for Driving a Magnetron

A one-chip class-E inverter controller is implemented in a 0.35 mum standard CMOS process. The control IC generates a control signal to turn on or off the insulated-gate bipolar transistor switch of the class-E inverter power supply driving a magnetron load which generates 2.45 GHz microwave for heating. It provides active power factor correction, soft start, and thermal protection. The rated RF output power of the magnetron is around 1.2 kW for a 100 V AC line, and an input power factor of over 0.98 is maintained. The proposed integrated solution gives better system performance with lower cost than conventional discrete solutions.

Voltage-Clamped Class-E Inverter With Harmonic Tuning Network for Magnetron Drive

A passive lossless snubber utilizing harmonic resonance is proposed for the voltage-driven class-E inverter. This snubber reduces the peak resonant voltage stress across the switch in class-E operation by adding the third-order harmonic current into the fundamental resonant part and can be extended to a higher-order network for further reduction. Though the principle is actually equivalent to the class-F operation in RF power amplifiers, it is first tried for the class-E inverter without a current source inductor. A series of analyses is performed to find component values that provide the optimum harmonic condition, and the experimental results from the inverter power supply for driving a magnetron are presented

A novel readout IC with high noise immunity for charge-based touch screen panels

The critical issues in charge-based touch screen panels for large size display are noise and speed. To solve these, this paper introduces a two-point relative sensing based ‘Delta-Integration’ scheme. It eliminates local noise and increases a readout difference between the touched and non-touched area. As a result, it can replace a high-resolution ADC with a comparator and counter. In addition, the single-bit conversion of Δ-integration method and the proposed wide-bandwidth charge amplifier solve a speed issue of a large display. The prototype chip is implemented in a 0.35-µm CMOS technology.

Power-efficient series-charge parallel-discharge charge pump circuit for LED drive

A charge pump drive circuit for LED lighting is proposed. This circuit is realized with repeated use of a compact unit module consisted of a capacitor and diodes. The series-charge and parallel-discharge operation gives the efficiency better than the conventional converters with AC line input. This paper also shows how to minimize the number of modules for a given number of LEDs. A prototype implemented the charge pump drive circuit shows a maximum efficiency of 95% for 22 LEDs in series with the AC line voltage of 220 Vrms.