M. Melito

A low-voltage MOSFET with small on-resistance: an extended characterization in high-efficiency power converter applications

The paper deals with a new concept applied in designing low-voltage power MOSFETs, which 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. The authors 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 enhancing of the device ruggedness. The high current handling in switching conditions (up to 150 A) with a breakdown voltage in the range between 20-50 V in a convenient package solutions allow to give the correct answers to the low-voltage range switch applications. The 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 traditional test circuit as well as in an actual AC motor drive for wheelchair applications is presented and discussed.

Snubberless balancement of series connected insulated gate devices by a novel gate control strategy

The series connection of insulated gate devices, such as MOSFETs or IGBTs, is increasingly used in high-voltage power converters where the demand for fast power switches is growing. The main problem in such an application is to guarantee the voltage balance across the devices both at steady-state and during switching transients, in order to avoid damaging overvoltages. In this paper, a novel approach is used to balance the voltage during switching transients by controlling the charge profile of the input gate capacitance. The main advantages of the proposed method consist in avoiding the common use of balancing capacitors in the output power side, and in working on the gate drive signals only. The application of the proposed gate drive technique is discussed first and then validated by experimental tests applied to the control of two series connected devices (MOSFETs or IGBTs). The proposed approach is also applicable for more than two devices. In particular, the validity has been proven by computer simulations for three components. Finally, a comparison is performed between the switching behaviors of two different configurations: a high-voltage application having for a high-voltage single switch device; or a series of two lower voltage rated devices. The advantage of the latter configuration, having the proposed active voltage balancing, over the former has been experimentally demonstrated with regard to the turn-off power losses.

Active voltage sharing of series connected strings of IGBT devices in bridge applications

The successful use of series connected strings of MOSFETs or IGBTs, requires equalizing the dynamic and static voltage sharing across the devices. The dynamic voltage imbalance is generally managed via the slope control of the output voltages by snubber capacitors, or by active balancing circuits on the gate side. In this paper, a novel approach, based on the control of the currents supplied to the gates, is proposed. The main issues related to the application in bridge configuration of series connected strings of devices are faced. Firstly, the voltage sensing circuit is analyzed in order to meet the needs of bridge circuits. Experimental tests are performed in order to evaluate the impact of the actual control actions on the devices. Advantages and disadvantages of the proposed active voltage sharing circuit are treated extensively, in order to give also experimental evidence to the switching power losses in comparison with conventional approaches.

Transient behavior of IGBTs submitted to fault under load conditions

The paper deals with the short circuit behavior during fault under load (FUL) conditions occurring on IGBT devices. The experimental switching transients in FUL with inductive load have been widely investigated. The devices have been tested in several working conditions accounting for the spread of the device characteristics, the parasitic due to the board layout, and the gate driving characteristics aiming to evaluate the switching performances and the influence of the parameters involved into the transient. The effect of the device temperature has been taken into account too. The experimental tests have been carried out using as a workbench a chopper circuit equipped with IGBT devices. As in medium and large power range converters the use of multiple string of IGBT devices is worth to be considered, the parallel and series connections experiencing FUL conditions have been also investigated.

A new high voltage power MOSFET for power conversion applications

The aim of this paper is to explore the switching capability of a new kind of high-voltage power MOSFET device called multiple drain mesh (MDmesh). This new power MOSFET shows very interesting characteristics in terms of both die size reduction and switching performances. By the used technological process a considerable reduction in silicon conduction losses per area unit has been observed, thus allowing a noticeable resizing of the devices and the use of smaller packages. Moreover, a strong reduction in the parasitic capacitance (i.e. gate charge) with an improved switching behavior has been observed. The power MOSFET that we are now introducing can replace standard power MOSFET devices in switch mode power supply (SMPS) or power factor correction (PFC) applications, thus allowing a valuable reduction of the power losses to be obtained and an increase in the converter efficiency, whereas the switching frequency is unchanged. This paper starts by describing the main technological issues of the new device, which is compared to more standard devices. The switching transients have been carried out looking for actual applications, and the advantages of the new device are discussed in terms of energy saving and performance improvement. Finally, a comparison with a standard device with the same voltage and current ratings is made and discussed, showing the improved performances of the new device.

Modeling and characterization of a merged PiN-Schottky diode with doping compensation of the drift region

In this paper standard-cell Schottky rectifiers along with silicon-based merged PiN Schottky (MPS) and PiN diodes, which are realized using a super junction technology, have been analyzed by conducting extensive device and mixed-mode simulations through two-dimensional finite-element grid. The main issues of concern with these devices such as the forward voltage-drop, the leakage characteristic and the reverse recovery are dealt with, by highlighting the superior performances exhibited by the MPS rectifier in respect to the PiN diodes. Basics on the used technology are also reported, by focusing on the high voltage capability obtainable along with the low forward voltage-drop during the on-state conduction. The reverse recovery behavior pertaining to the MPS diode has been analyzed by resorting to several simulations of the internal plasma dynamics.

On the series connection of insulated gate power devices

The series connection of insulated gate devices (IGBTs and MOSFETs) is treated with reference to different approaches which ensure a balanced voltage sharing. Both load-side and gate-side techniques are discussed, and their merits and demerits are highlighted. A novel approach, which intervenes during the rise time or fall time of the collector voltages, is discussed and compared to the alternative solutions. Laboratory tests on two IGBT devices are carried out according to the analyzed techniques. Finally, the disadvantages of the multiple connections are discussed in terms of switching speed reduction and power loss increase.

Bipolar-MOS monolithic cascode switch in VIPower technology

In this paper a bipolar-power MOSFET cascode monolithic device, realized in ST-SGS Thomson VIPower (Vertical Intelligent Power) Technology called M3, is presented. The basic device features a three-stage deep-base NPN BJT and a vertical power MOSFET, realized inside the emitter of the trilinton output stage itself for emitter switching. The paper starts with a survey of the main characteristics of the SGS-Thomson Vertical Intelligent Power technology. Then the switching performances of the device are compared to power MOSFET and fast-switching IGBTs in terms of their forward conduction current density turn-off times and breakdown voltages.<<ETX>>

Design considerations on the low-voltage MOSFET applications to wheelchair drive systems

The paper deals with the application of MOSFETs, as switching devices, in a low-voltage power converter, which is devoted to an electric-driven wheelchair. The characteristics of the MOSFETs have a major impact on the whole performances of the drive system. The used devices are out of the traditional cell-structure MOSFETs, and they present interesting characteristics due to the advanced design rules typical of the VLSI processes. These MOSFETs can carry current up to 150 A, with a breakdown voltage in the range 20 V-50 V. The paper starts with the description of some technological issues. In particular, the paper focuses on the innovations and the improved performances in comparison to those of standard devices. Laboratory tests are carried out aiming to characterize the device looking for the specific application in a full bridge inverter. Finally, considerations and design criteria, in order to reduce the total power losses in the actual AC motor drive for wheelchair applications, are presented.

Short circuit transient behavior of IGBT devices in series connections

The need of devices for medium-range power converters gives rise to a growing interest for the series connections of IGBTs. In this case the control of the voltage sharing across the string of series-connected devices as well as their protection during the short circuit transients are important issues. In this paper is presented an exhaustive analysis of the electrical quantities and device parameters affecting the voltage sharing across the series strings of IGBTs in short circuit conditions In particular, hard switching fault (HSF) and fault under load (FUL) are investigated, in the case of series connections of devices, by carrying out simulation runs and experimental tests in order to understand the behavior of the IGBTs in these critical conditions. Advantages and disadvantages of the voltage sharing techniques are discussed with reference to the failure in short-circuit occurring on the series connection of devices.