Research Of Power Devices Used In Low-Voltage Buck Converters

The aim of this paper is to find a new device, which should have rather low power loss, to meet rigorous demands required by power devices used in power supply circuit of CPU for laptops. With the performance improvement of CPU, power loss consumed by power devices become relative high and can not be ignored. Power MOSFET, which is now widely used in power supply circuits, will have small space to develop due to structure limitations produced by itself. Therefore, more and more people in the world pay their attentions to normally-off JFET and normally-on JFET. A new structure of JFET is proposed by us based on the structure of existing trench JFET, namely replacing part of Si under the gate to SiO2, which is insulating and has 1/3 inductivity as low as Si, in order to reduce Gate-Drain capacity CGD, and consequently reduce switching loss. This paper study static and switching characteristics by simulating five different devices—normally-off JFET, normally-off JFET with BOX( Buried Oxygen), normally-on JFET, normally-on JFET with BOX, and trench MOSFET. Finally, the power losses of different devices are figured out and are compared with each other. According to the result, normally-on JFET,especially normally-on JFET with BOX, has considerable reduce of power loss than MOSFET when ID=15A, and with the accretion of the frequency of switching and decrease of ID, the lower power losses can be grain by JFET. For example, when ID=4A,f=2MHZ, the power losses of normally-off JFET, normally-off JFET with BOX, normally-on JFET, and normally-on JFET with BOX are reduced 31.1%, 34.6%, 34.2%,and 47.6% than that of MOSFET respectively。...