1. ABSTRACT

This paper deals with a new concept applied in designing low-voltage power MOSFETs that are suitable

for high-current low-voltage converter applications. The layout of the proposed device family overcomes

the traditional cell structure by a new strip-based geometry. They present interesting characteristics due

to the advanced design rules typical of VLSI processes and strong reduction of the on-state resistance.

Further, the technology process allows a significant simplification of the silicon fabrication steps, thus

allowing to enhance the device ruggedness. The high current handling in switching conditions (up to

150A) with a breakdown voltage in the range between 20-50V in a convenient package solution give the

correct answers to the low-voltage range switch applications. This paper starts with the description of the

main technology issues in comparison with that of standard devices, particularly focusing on the

innovations and the improved performances. Moreover, a detailed characterization of the MOSFET

behavior in a traditional test circuit as well as in an actual AC motor drive for wheel chair applications are

presented and discussed.

2. INTRODUCTION.

Higher efficiencies are expected nowadays in the field of power converters for battery-powered systems.

As industrial and commercial applications of these systems are increasing more and more (laptops,

portable equipment, home appliances, electric assisted bikes, electric scooters, wheel chairs, mobiles,

etc.), higher efficiencies become of major interest in order to meet the user requirements of long-lasting

behavior with the same battery charge. To do that, researchers have made dramatic efforts in designing

new converter structures, in increasing the converter switching frequency and in conceiving innovative

power devices.

Generally speaking, battery powered systems require low-voltage switching devices (<100V). Power

MOSFET devices dominate in this voltage range due to their attractive characteristics of high switching

speed and easy driving capability. On-state losses of MOSFETs are of major concern on their total power

loss balance, especially in case of converters with low or medium switching frequency. Since on-state

modern MOSFETs are realized with a cell-based layout, which determines low on-state resistance. The

increase of the cell density allows to further reduce the on-state resistance, thus increasing the current

capability per device area-unit. However, for today’ s state-of-the-art MOSFETs, ulterior reduction of the

on-state resistance by this conventional layout is impeded since this approach is reaching its own

physical limit [1]. The need of innovative approaches arises in order to overcome the limit of this

technology.

January 2002

1/14

AN1506

APPLICATION NOTE

A MOTOR DRIVES SYSTEM FOR

WHEELCHAIR APPLICATIONS

G. Belverde - C. Guastella - M. Melito - A. Raciti