Kei Okada

Bio: Kei Okada is an academic researcher. The author has contributed to research in topics: Flyback transformer & DC-to-DC converter. The author has an hindex of 1, co-authored 1 publications receiving 196 citations.

Dc-to-dc converter

Abstract: A transformer has a primary winding connected between a pair of dc input terminals via an on-off switch, and a secondary winding connected between a pair of dc output terminals via a rectifying and smoothing circuit The output voltage applied from the rectifying and smoothing circuit to the load is held constant by switching the input voltage through feedback control The switch is driven in either of two different prescribed modes depending upon whether the converter is under normal or light load In order to ascertain the load magnitude a flyback period determination circuit is connected to a tertiary winding of the transformer for providing a signal indicative of a flyback period during which a flyback voltage exists across the transformer tertiary after the switch is turned off each time Each flyback period is compared with two different reference periods of time for hysteretic determination of whether the converter is under normal or light load Several other embodiments are disclosed

Distributed Power Harvesting Systems Using DC Power Sources

Abstract: A system and method for combining power from DC power sources. Each power source is coupled to a converter. Each converter converts input power to output power by monitoring and maintaining the input power at a maximum power point. Substantially all input power is converted to the output power, and the controlling is performed by allowing output voltage of the converter to vary. The converters are coupled in series. An inverter is connected in parallel with the series connection of the converters and inverts a DC input to the inverter from the converters into an AC output. The inverter maintains the voltage at the inverter input at a desirable voltage by varying the amount of the series current drawn from the converters. The series current and the output power of the converters, determine the output voltage at each converter.

Circuits and methods for driving light sources

Abstract: A driving circuit includes a first inductor coupled in series with a light source for providing power to the light source. A controller coupled to the first inductor can control a switch coupled to the first inductor, thereby controlling a current flowing through the first inductor. A current sensor coupled to the first inductor can provide a first signal indicative of the current flowing through the first inductor, regardless of whether the switch is on or off. The switch is controlled according to the first signal. A second inductor magnetically coupled to the first inductor is also electrically coupled to the first inductor via a common node between the switch and the first inductor for providing a reference ground for the controller. The reference ground is different from the ground of the driving circuit.

Power control system for current regulated light sources

Abstract: A light emitting diode (LED) lighting system includes a PFC and output voltage controller and a LED lighting power system. The controller advantageously operates from an auxiliary voltage less than a link voltage generated by the LED lighting power system. The common reference voltage allows all the components of lighting system to work together. A power factor correction switch and an LED drive current switch are coupled to the common reference node and have control node-to-common node, absolute voltage that allows the controller to control the conductivity of the switches. The LED lighting system can utilize feed forward control to concurrently modify power demand by the LED lighting power system and power demand of one or more LEDs. The LED lighting system can utilize a common current sense device to provide a common feedback signal to the controller representing current in at least two of the LEDs.

Monitoring of Distributed Power Harvesting Systems Using DC Power Sources

Abstract: A monitoring system and method for monitoring performance of individual powers sources in a distributed power source system A monitoring module is coupled to each of the power sources, or to each string of serially connected power sources, to monitor and collect data regarding current, voltage, temperature and other environmental factors at the power source The collected data is transmitted over a power line to a central analysis station for analysis Data collected from each source indicates malfunction or degradation at the source Comparison of data collected from adjacent sources filters for environmental factors impacting neighboring sources such as cloudy days for a solar panel Comparison of data collected from the same source at different times indicates soiling or degradation of the source with time or periodic events such as a moving shade from an adjacent building

Method for distributed power harvesting using DC power sources

Abstract: A system and method for combining power from DC power sources. Each power source is coupled to a converter. Each converter converts input power to output power by monitoring and maintaining the input power at a maximum power point. Substantially all input power is converted to the output power, and the controlling is performed by allowing output voltage of the converter to vary. The converters are coupled in series. An inverter is connected in parallel with the series connection of the converters and inverts a DC input to the inverter from the converters into an AC output. The inverter maintains the voltage at the inverter input at a desirable voltage by varying the amount of the series current drawn from the converters. The series current and the output power of the converters, determine the output voltage at each converter.