Ken Matsuura

Power-density development of a 5MHz-switching DC-DC converter

This paper presents the power-density development of a high-frequency isolated DC-DC converter for ICT equipments. This technique results in a prototype of a 5MHz DC-DC converter module. In order to realize a prototype of the high-frequency isolated DC-DC converter, its topology is selected to be a half-bridge type current-mode resonant converter, and switching power devices of GaN-FET and Si-SBD and the transformer composed of a nickel-zinc ferrite core are utilized. As a result, a 5MHz isolated DC-DC converter with the input/output voltages of 48V/12V and the power rating of 120W has been fabricated, and the high power-density of 14W/cm3 has been performed.

Improvement of transient response in high-current output DC-DC converters

Concerning a low-voltage and high-current output DC-DC converter such as a voltage regulator module used for a 64-bit microprocessor, synchronization with paralleled current-doubler rectifiers has been considered for improvement in dynamic response. As a result, the output voltage deviation of 50 mV at a slew rate of 300 A//spl mu/s has been performed on a prototype with an output of 1.3 V/130 A.

5MHz PWM-controlled current-mode resonant DC-DC converter with GaN-FETs

In this paper, a proposed pulse width modulation (PWM) control method for the isolated current-mode resonant DC-DC converter with MHz level switching frequency is presented. The circuit topology is same as a conventional resonant converter with synchronous rectification and without any additional components. The control technique for the output voltage regulation is proposed with the unique PWM control for synchronously-rectifying switches. By using the transformers leakage inductance and the PWM control, the boost conversion can be realized. In addition, to achieve the zero-voltage switching (ZVS) operation, phase-shift between primary and secondary-side switches is adapted. The ZVS operation can maintain for primary-side switches. In this paper, proposed technique for achieving stable ZVS operation has been discussed. Some experiments have been done with 5MHz isolated DC-DC converter which has Gallium Nitride field effect transistor (GaN-FET), and the total volume of the circuit is 16.14cm3. The data show that the maximum power efficiency is 89.4%.

5MHz PWM-controlled current-mode resonant DC-DC converter using GaN-FETs

In this paper, the method of the realization of a MHz level switching frequency DC-DC converter for high power-density is presented. For high power-density, Gallium Nitride field effect transistor (GaN-FET) and current-mode resonant DC-DC converter are adopted. In addition, the proposed pulse width modulation (PWM) control method which is suitable for the isolated current-mode resonant DC-DC converter operated at MHz level switching frequency, and the novel primary-side zero voltage switching (ZVS) turn on method for the proposed PWM control are presented. Some experiments have been done with 5 MHz isolated DC-DC converter which has GaN-FET, and the total volume of the circuit is 16.14 cm3. With the proposed PWM control method, input voltage range is 36-44 V, and maximum load current range is 8 A at Vi = 44 V. The primary-side ZVS turn on is confirmed, and the maximum power-efficiency is 89.4%.

Five-Megahertz PWM-Controlled Current-Mode Resonant DC–DC Step-Down Converter Using GaN-HEMTs

High power efficiency and high power density are required in regulated isolated dc-dc converters. In this paper, a novel pulsewidth modulation (PWM) control method that is suitable for an isolated current-mode resonant dc-dc converter operated at a megahertz-level switching frequency is proposed. The output voltage with the proposed method can be regulated with no additional components at a fixed switching frequency. In addition, the zero-voltage switching (ZVS) of primary-side switches at turn on can be maintained. The principle of the proposed method and the method of the ZVS operation in the proposed method are explained. Some experiments have been performed with a 5-MHz isolated step-down dc-dc converter using gallium nitride high-electron-mobility transistors; the output voltage is 12 V, and the total volume of the circuit is 16.14 cm3. With the proposed PWM control method, the input voltage range is 42-45.5 V, and the maximum load current range is 10 A at Vi = 45.5 V. The ZVS of the primary-side switches at turn on is confirmed in all experimental regions, and the maximum power efficiency is 89.2%.

Reduction technique of leakage flux effects on GaN-HEMTs in 5 MHz / 100 W isolated DC-DC converters

To achieve high power-density isolated dc-dc converter, gallium nitride high electron mobility transistors (GaN-HEMTs) and planar transformer have been used. Also, for the high power-density design, these components are placed close to each other. GaN-HEMTs are significantly affected by the leakage flux of the planar transformer, because of their lateral structure. Therefore, the mutual effects of the components are needed to take into account. This paper presents the leakage flux effects of the planar transformer on GaN-HEMTs in 5 MHz isolated dc-dc converter. Moreover, to suppress the effects, the method using the magnetic shield as the part of the printed circuit board (PCB) layout has been proposed. The effects and the proposed method have been analyzed by finite element method (FEM) with Maxwell 3D. Some experiments have been done with 5 MHz unregulated LLC resonant dc-dc converter with GaN-HEMTs; the input voltage is 48 V, the output voltage is 12 V, and the size is 17 mm × 25 mm × 6.5 mm. From the experimental results, by inserting the magnetic shield, the load current range is improved from 6 to 8 A. In addition, the maximum temperature is improved 17.1 °C, and the power efficiency is increased 1.58 % at 6 A.

Influence of parasitic components on MHz-level frequency LLC resonant DC-DC converter

In this paper, the influence of parasitic components of LLC resonant dc-dc converters operated at MHz-level switching frequency is investigated. In MHz-level switching frequency, value of the parasitic components are getting closer to value of circuit parameters. Therefore, influence of the parasitic components cannot be neglected even in the initial step of the circuit design. In particular, undesirable boost conversion is happened at light load condition with parasitic components, which disturbs the output voltage control. Therefore, it is very important to reveal what happened with the parasitic components. In this paper, to verify the influence of the parasitic components, some analyses have been done. With the analysis results, the influence of the parasitic components has been revealed. Some experimental results have been conducted with an isolated step-down dc-dc converter with Gallium Nitride High Electron Mobility Transistors (GaN-HEMTs); the input voltage is 53V, the load current range is less than 1A, and the maximum switching frequency is about from 3 to 5.5MHz. From the experimental results, it revealed that secondary-side current transformer LCT2 and secondary-side junction capacitance Cj greatly affect the static characteristics at MHz-level switching frequency. Therefore, by minimum load current setting and number of parallel of secondary-side diode, using LCT2 for measuring secondary-side winding current is decided.

High frequency PWM-controlled current-mode resonant DC-DC converter with boost conversion

In this paper, a new pulse width modulation (PWM) control method for the isolated current-mode resonant converter with a fixed switching frequency is presented. The circuit topology is the same as a conventional resonant converter with synchronous rectification and without any additional components. The control technique for the output voltage regulation is proposed with the unique PWM control for synchronously-rectifying switches. By using the transformers leakage inductance and the PWM control, the boost conversion can be realized. Also, the zero-voltage switching (ZVS) operation can be done for primary switches, simultaneously. Some experiments have been done with 5MHz isolated DC-DC converter which has Gallium Nitride field effect transistor (GaN-FET).

Considerations of Physical Design and Implementation for 5 MHz-100 W LLC Resonant DC-DC Converters

Recently, high power-density, high power-efficiency, and wide regulation range isolated DC-DC converters have been required. This paper presents considerations of physical design and implementation for wide regulation range MHz-level LLC resonant DC-DC converters. The circuit parameters are designed with 3–5 MHz-level switching frequency. Also, the physical parameters and the size of the planar transformer are optimized by using derived equations and finite element method (FEM) with Maxwell 3D. Some experiments are done with prototype LLC resonant DC-DC converter using gallium nitride high electron mobility transistors (GaN-HEMTs); the input voltage is 42–53 V, the reference output voltage is 12 V, the load current is 8 A, the maximum switching frequency is about 5 MHz, the total volume of the circuit is 4.1 cm3, and the power density of the prototype converter is 24.4 W/cc.