Koosuke Harada

A PWM controlled simple and high performance battery balancing system

For balancing battery cells connected in a series string, a simple and high performance battery balancing system is proposed. In this system, a technique of DC to DC converter with PWM control is used for balancing all cell voltages completely. The switching surge and noise are made small by soft switching with inductor commutation. This system is suitable for electric vehicles, hand-held personal computers, UPS etc.

Analysis of Double Step-Down Two-Phase Buck Converter for VRM

A novel two-phase buck converter suitable to apply the power supplies for MPU is proposed. Compared to conventional two-phase buck converter, the proposed converter essentially has double step-down ratio as Eo/Ei = D/2 and high efficiency is realized by reducing the switching loss of the switching elements. In addition the current ripple of the output smoothing capacitor is improved to the same value as that of conventional four-phase buck converter. Moreover the current unbalance between two inductors in each phase is removed automatically without any current sensing means. The above fine characteristics are simply achieved an additional capacitor

A Novel Three-Phase Buck Converter with Bootstrap Driver Circuit

Analysis and design consideration of the novel three phase converter with new bootstrap driver circuit for the mobile micro processor in the laptop PC are presented. The voltage conversion ratio of the proposed converter is one third of the duty cycle. The voltage across the switches during switching operation is one-third of the input source voltage. The current ripple of the output smoothing capacitor is the same as that of conventional five-phase buck converter. The current balance of the respective phases is automatically achieved without any current sensing means. The above fine characteristics are simply achieved with two additional capacitors.

Investigation on the Ripple Voltage and the Stability of SR Buck Converters With High Output Current and Low Output Voltage

Synchronous rectifiers (SRs) composed of MOSFETs have recently been employed to replace the conventional rectifiers with diodes. SRs are widely used in switched-mode power supplies with low output voltage and high output current for efficiency improvement. Owing to the high-efficiency characteristic, it is adequate to use an SR buck converter in a voltage regulator for powering a central processing unit. Normally, such SR buck converter must operate at fairly high switching frequency for miniaturizing a whole circuit and achieving a fast response. However, at the conditions of low output voltage, high output current, and high switching frequency, the influence of parasitic elements to circuit operation will become extremely obvious. Therefore, the design considerations concerning the ripple voltage and the stability of such SR converters should be carefully investigated and clarified. By establishing the equivalent circuit and using a state-space averaged method, the ripple ratio of output voltage and the static and dynamic characteristics of the SR buck converter with nonnegligible parasitic elements are obtained. Thus, the design criteria concerning the output ripple voltage and the stability are clarified.

Self turn-on loss of MOSFET as synchronous rectifier in DC/DC buck converter - in case of a low driving impedance -

In this paper we present a kind of losses on MOSFET as a synchronous rectifier which is very difficult to remove in compare with the other losses. For high performance, downsizing and lightweight of digital equipment as a personal computer, digital ICs are developed with high speed and densely integrated. The supply voltage for these ICs becomes lower and the supply current becomes higher. A buck converter is widely used as a DC/DC converter for this purpose. In the buck converter, a synchronous rectifier of MOSFET with ultra low on-resistance is widely used as a low-side switch for higher conversion efficiency instead of a Schottky barrier diode as a free wheel diode. When the high-side switch is turned on as the low-side switch is off, the drain-source voltage of the low-side switch rises rapidly and the gate-source voltage rises simultaneously through the drain-gate capacity. As a result, the gate-source voltage becomes up to the gate threshold voltage and the low-side switch becomes active state and the drain current flows. We named this phenomenon dasiaself turn-onpsila where the loss occurs in the low-side switch.(Murata et al., 2003) in this paper a precise analysis of the self turn-on phenomenon is presented and the experiments for verification are also presented.

A self oscillated half bridge converter using impulse resonant soft-switching

A novel circuit of DC-TO-DC converter for the battery charger of telecommunication equipment is proposed. For the circuit, a novel self oscillated half-bridge converter with an impulse resonant soft-switching using saturating inductance of the oscillator is developed. In this converter, the self oscillated frequency control circuit has the switches operated soft-switching by impulse charging and discharging the parasitic capacitance of the main switches and also driving circuit of the switches. The complete operating principle and theoretical analysis on the proposed converter are provided. The experimental results of a 2 kW prototype converter operating at 100 kHz with 200 V AC input are presented and discussed.

A Novel Multi-Phase Buck Converter for Lap-top PC

We propose a novel multi-phase buck converter with a simple gate drive circuit, which is suitable for mobile microprocessors of lap-top computers. In case of the three-phase construction, the duty-cycle of this converter is extended to three times of that of the typical buck converter because the voltage conversion ratio is given as V0/Vi = D/3. The switching loss and switching stress are reduced sufficiently because the switching operation is achieved by one-third of the input source voltage (Vi/3). The current ripple of the output smoothing capacitor is the same as that of conventional five-phase buck converter. The current unbalance between the respective phases is removed automatically and completely without any current sensing means. The above fine characteristics are simply achieved with two additional capacitors.

A double step-down two-phase buck converter for VRM

In order to provide the power to the microprocessor, a novel two-phase converter with the large step down conversion capability is presented. The voltage conversion ratio of this converter is given as Eo/Ei = D/2. The switching loss and the output voltage ripple are also reduced. Moreover the current unbalance between two inductors in each phase is removed automatically without any current sensing means

A novel two-phase buck converter with two cores and four windings

A novel two-phase buck converter with two cores and four windings is proposed. In this converter, a capacitor is added to the primary side for dividing the input source voltage into one half in the similar way as that of a typical half bridge converter. The voltage conversion ratio is given as one fourth of the duty cycle with unity turns ratio of the each transformer. The output capacitor ripple and the switching losses are well reduced. The currents in each phase are balanced automatically without any current sensing methods.

Novel DC switch and DC socket for high voltage DC power feeding systems

This paper presents a novel and reliable DC switch and DC socket for high voltage DC power feeding system, in which the arc does not occur when the are turned on/off and inserted/removed, respectively. The novel prototype DC switch and DC socket have been made. Both are almost same circuit configuration and operation principle and then composed of two mechanical relays and a single MOSFET. It has been tested for the proposed DC switch to protect not only the arc but also thermal problem. As a result, it is confirmed that the arc thermal problem do not occur when the MOSFET and relays are turned on/off and relays are on in steady state, respectively, and that they have the excellent performance characteristics using simple semiconductor snubbers with the overvoltage clamp function.