Shigeharu Yamashita

New switching control for synchronous rectifications in low-voltage paralleled converter system without voltage and current fluctuations

Synchronous rectifiers (SRs) used in paralleled converter system cause several problems such as surge voltage, inhalation current and return current. Normally, to avoid the problems, SR operation is stopped in light load. However, at the same time, voltage fluctuation occurs, which causes serious errors in semiconductor devices such as CPU and LSI operating with very low voltage. Moreover, unstable current fluctuation occurs due to the voltage fluctuation in the paralleled system with current-sharing control. This paper proposes new switching control methods for rectifiers to reduce the voltage and current fluctuations. Experimental results are shown to confirm the effectiveness of the proposed methods.

High-efficiency switching power supply unit with synchronous rectifier

This report describes an insulation-type switching power supply unit (DC/DC power converter) for mainframe computers that uses a newly developed synchronous rectifying circuit for the secondary rectification component. Compared with conventional switching power supply units, this unit offers 6% higher processing efficiency, and power output per unit volume that has been boosted by 1.75 times. As a result, this unit provides high efficiency, low voltage and high power output.

Abnormal Phenomenon of Output-Voltage Increase and Its Solution in a Parallel-Redundant DC-DC Converter System with Current Sharing Control

Abnormal phenomenon of output voltage is observed in a paralleled N+1 redundant DC-DC converter (DDC) system. The phenomenon is caused by a current sharing control under the condition of periodic load change, resulting in output-voltage increase. The mechanism of the phenomenon is analyzed with a circuit simulator and confirmed by experiment. A new type of current sharing circuit is proposed to solve the problem

Water-cooled switching power supply

The authors describe a novel water-cooled switching power supply that is one-third of the size of the conventional air-cooled 2.2 kW power supply. A size reduction of one-third makes it possible to locate the supply nearer the logic circuits. To achieve this size reduction: (1) the size of the output filter was reduced and a forward two-phase switching PWM (pulse width modulation) topology with a switching frequency of 200 kHz was used; and (2) the main switching elements and output diodes are water-cooled using the same coolant that is used for the logic circuits. Since these elements account for as much as 70% of the overall losses in a switching power supply, this technique resulted in a better than 83% reduction in the volume of the heat sink. The performance of the switching power supply is described, with emphasis on the circuit and the cooling system.<<ETX>>

Gain controlled high efficiency power factor correction circuit

The purpose of this study is to improve the efficiency of a boost-type power factor correction (PFC) circuit with a digital controller. One of the biggest losses in PFC circuits is the switching loss. Switching loss can be reduced by low boost ratio operation, but these results in a greater voltage drop at transient response. The voltage drop can be suppressed by using a high gain setting for the voltage control loop, but this lowers the power factor, which creates a harmonic distortion of the AC power line. To improve this trade-off, we developed a gain control method that adjusts the gain to high only at the moment of transient response. This method improves both the efficiency and the power factor of PFC circuits. We implemented the proposed method using a digital controller and demonstrated a power factor improvement of 0.08 points and an efficiency improvement of 0.4 points for a 2.5 kW PFC circuit.