G. Busatto

Series connection of high power IGBT modules for traction applications

IGBT series-connected power switching circuit is presented. Voltage balance on IGBTs is ensured by means of a simple auxiliary circuit applied directly on the high power inverter used in hard switching applications. Analysis in terms of dissipated energy, collector overvoltage and switching frequencies, comparing performances of a single high voltage IGBT (3300 V) module and two series connected 1700 V IGBTs is reported. An extended experimental analysis is also reported. Both analysis confirm the advantages in using two series connected IGBT in substitution of a single high voltage module in terms of power losses and switching performances

Experimental and numerical investigation on MOSFET's failure during reverse recovery of its internal diode

The failure of the power MOSFET during the reverse-recovery of its intrinsic body-source diode used as a fly-back element in a half-bridge configuration has been investigated. The experimental waveforms have been studied based on the analysis carried out by a mixed device and circuit simulator. According to the test conditions, it is shown that during the diode reverse recovery either a carrier current or a displacement current contribute to the activation of the parasitic BJT, which may cause the failure of MOSFETs. Among the parasitic elements inherent in the MOSFET structure, the capacitance associated to the gate oxide and the resistance of the polysilicon gate are shown to play a relevant role in the activation of the parasitic BJT due to a displacement current. The activation of the BJT due to carrier current, on the other side, is essentially dependent upon the resistances of the distributed base and of the body-source contact.

Comparative analysis of power bipolar devices

A comparison between bipolar Darlington, insulated gate bipolar transistor (IGBT), bipolar mode field effect transistor (BMFET), and power MOS devices is presented based on an experimental investigation performed on devices with similar geometrical characteristics and blocking voltage capabilities. The main device characteristics (conduction characteristics, switching performances, power dissipation, power ratings, etc.) are presented and compared in order to obtain comprehensive guidelines for finding their fields of application. It is shown that, for higher frequency switching application, MOS devices are the most suitable, but they are very expensive in terms of silicon area used. For frequencies less than 20 kHZ, BMFETs have better performance than IGBTs in terms of power losses. On the other hand, the IGBT is a voltage-controlled device and thus has fewer problems with its driving circuit.<<ETX>>

Nondestructive testing of power MOSFET's failures during reverse recovery of drain-source diode

The failure of power MOSFET during reverse recovery of its intrinsic drain-source diode is experimentally studied by means of a nondestructive tester. The analysis is based on the observation of the waveforms during the failure which shows the evidence of the activation of parasitic bipolar transistor. This paper advances the hypothesis that the failure mechanism is strictly related to how this transistor is being activated during reverse recovery. In particular, for higher values of dI/sub D//dt, the bipolar parasitic transistor on small area of the chip is activated at the early beginning voltage rise. Device failure is then caused by the second breakdown of this transistor which takes place during its turn-off.

EMI analysis in high power converters for traction application

The driving improvement in terms of IGBT switching losses reduction is accompanied by a significant increase of EMC noise problems. In this paper, the authors focused their attention on the electromagnetic noise radiated by the high voltage high power IGBT modules during the inductive turn-on. The noise variation and the dependence of each IGBT commutation phase is investigated by means of an experimental set-up that reproduces a real inverter used in railway applications. The EMC measures have been executed by means of an original experimental method that is most indicated for the high power inverter systems. The experimental and the simulation results demonstrate that the radiated electromagnetic noise is stimulated by the dv/dt voltage gradient and the amplitude of the noise is proportional to it. The main high frequency harmonic components of the emitted signal are stimulated by the voltage variations across the device during the first phase of the turn-on, whereas the signal is emitted by the freewheeling diode during the second phase of its reverse recovery when this diode is stimulated by a large voltage variation

Measurement of the BJT activation current during the reverse recovery of power MOSFET's drain-source diode

A new and simple method to measure the activation current of the parasitic BJT in the drain-source MOSFETs diode is presented. Based on the evaluation of the stored charge at supply voltages lower than the maximum reverse voltage of the device, accurate and safe measurements have been performed at forward current levels up to the MOSFETs maximum current rating.

Experimental optimisation of high power IGBT modules performances working at the edges of their safe operating area

An experimental characterization of new 3300 V - 1200 A IGBT modules both at high temperature and for output currents beyond SOA, at turn-off and in short circuit conditions, is presented. Moreover a new driving strategy that improves, in comparison with conventional driving methods, IGBT turn-on on inductive load, in terms of power dissipation, is reported. Results demonstrate that, in principle, it is possible to operate at larger current than RBSOA limits and at temperature of 145 /spl deg/C. As regard turn-on operation, up to 37% dissipated energy reduction can be obtained with the innovative on-gate control. All the experimental study has been performed by means of a non-destructive experimental set-up, where IGBT modules are switched in presence of a protection circuit that is able to prevent device failure at the occurrence of any possible unstable behaviour.

Physical modeling of bipolar mode JFET for CAE/CAD simulation

A circuit model of a power bipolar JFET, based on a specific formulation of its charge control model,is presented. The circuit obtained accurately describes both unipolar and bipolar modes of operation of the device, and is presented in a form suitable to be incorporated in circuit CAD (computer-aided design) simulators. The model was developed on a physical basis, and its parameters can in principle be directly computed from geometrical and physical characteristics of the device. The author also presents the implementation of the model into the version 4.02 of PSPICE obtained by modifying a device subroutine. >

Experimental measurements of recombination lifetime in proton irradiated power devices

Experimental measurements of the recombination lifetime profile induced by proton implantation processes are presented. Results show the capability of the differential technique to monitor lifetime engineering processes.

Performance analysis of a Bipolar Mode JFET (BMFET) with normally off characteristics

The fabrication and the characterization of a family of power Bipolar Mode JFETs (BMFET) is reported. In these devices, blocking voltages up to 1000 V or currents up to 18 A (corresponding to 800 A/cm2) have been obtained. Results allow to get an insight in the physics of operation of the BMFET, to define their theoretical limits of operation, and to understand the reasons for the superior performance of the present device, with respect to the Bipolar Transistor.