Fumikazu Takahashi

Current ripple reduction technique of DC/DC converter

This paper presents a novel method to reduce the current ripple caused by the variation of inductor for a DC/DC converter. The presented method is to increase the switching frequency to keep constant current ripple when the inductance changes. Therefore, no extra component is required. The problem will be described first and the related method is presented. An experimental DC/DC converter is implemented which is with input voltage of 12 V, output voltage of 1.5 V, output current of 10 A, and switching frequency of 200-250 kHz. Finally, experimental results derived from the designed digital-controlled DC/DC converter are included for confirmation.

Current sensing methods for standby power control of digital-controlled DC/DC converter

The main theme of this paper is to study the current sensing methods for standby power reduction control of digital-controlled DC/DC converter. These methods include using transformer of full-bridge converter, coupling inductor and ORing MOSFET. The most suitable sensing method was verified with a digital-controlled 500W class DC/DC converter (input/output voltage: 400V/12V). Experimental results derived from digital-controlled DC/DC converter using the TI DSP (TMS320F2812) as the control platform show that current sensed by voltage across ORing MOSFET method provides superb solution. This method offers linear relationship between output voltage of sensing circuit and load current while not causing response delay under standby conditions and thereby truly reflecting accurate standby conditions.

Digital-controlled power factor corrector with transition current mode control without zero current detection

It is well known that transition current mode control for power factor corrector can reduce the reversal recovery loss for the diode. This method can be realized using discrete control integrated circuit which requires zero-crossing detection circuit. In this paper, a novel control technique for digital-controlled power factor corrector to achieve transition current mode control is proposed. The switching period to retain zero current switching is predicted and the turn-on period is determined by the voltage controller. Experimental results derived from a DSP-based controller are presented for confirmation. The power factor corrector is with 100 V/AC input and 400 V/DC output. Its power rating is 250 W. Experimental results show that the power factor is higher than 0.98, efficiency is greater than 94% and current total harmonics distortion (THDi) is smaller than 4% under full load condition and confirms the above-mentioned claims very well.