The robustness of series-connected high power IGBT modules

The behaviour in terms of robustness of series-connected high power IGBT modules is presented, arranged in a topology which ensures voltage balance on IGBT’s and diodes by means of a simple auxiliary circuit applied directly on the high power devices, which are used in hard switching mode. Analyses in terms of IGBT and diode SOA (safe operating area), collector to emitter voltage gradient and short circuit condition are reported as well as an extended experimental characterisation. Both analyses confirm superior switching rating and system reliability, by using two series-connected IGBT in substitution of a single module, same current and double voltage rated. Moreover, thanks the auxiliary circuit presence, the robustness of total system is maintained also in extreme operating conditions.     

The high frequency behaviour of high voltage and current IGBT modules

Sharp voltage gradients act as a stimulus for high power IGBT modules, which can exhibit a potentially instable high frequency behaviour. In fact, they can act as a radio frequency amplifier and, in particular operating conditions, the interaction between the device and the control or the external circuit can cause self-sustaining oscillations or the enhancement of the unevenness in current distribution inside a power module thus having a significant impact on the reliability of the power converter. Moreover, this RF amplification worsen the generated EMI (Electro Magnetic Interference). This paper presents an extensive experimental investigation about the high frequency behaviour of IGBT high power modules. The measurements were performed by means of an original experimental set-up that was specifically conceived and constructed. The data are analysed with the help of a theoretical small signal model which is able to describe RF behaviour of high power IGBT modules.     

Chlorpromazine inhibits tumour necrosis factor synthesis and cytotoxicity in vitro

Chlorpromazine (CPZ) has been previously shown to protect against endotoxin [lipopolysaccharide (LPS)] lethality and inhibit the release of tumour necrosis factor in vivo. We investigated at the cellular level whether this was due to direct inhibition of tumour necrosis factor-alpha (TNF-alpha) synthesis, using LPS-stimulated THP-1 human monocytic leukemia cells. We also studied the effect of CPZ on human TNF-alpha action by assessing TNF-alpha cytotoxicity on mouse fibrosarcoma L929 cells. CPZ (1-100 microM) inhibited TNF-alpha production in THP-1 cells in a dose dependent manner by a maximum of 80%. This effect was comparable to that of two well-known inhibitory drugs, dexamethasone and cyclicAMP. Inhibition was also evident at the mRNA level. On the other hand CPZ (10-25 microM) also inhibited TNF-alpha activity: in fact it reduced the cytotoxicity of TNF-alpha on L929 cells (EC50 was increased four times) and could provide protection even as a post-treatment. CPZ inhibited TNF-induced apoptosis in L929 cells, as detected by analysis of nuclear morphology. However, since we showed that apoptosis was very limited, and was not the main mode of cell death in our conditions, this could not explain the overall protection. Since CPZ did not interfere with either the oligomerization state of TNF-alpha or its receptor binding, our data suggest that it reduced cytotoxicity by inhibiting some steps in the TNF-alpha signalling pathways.     

Advanced RBSOA analysis for advanced power BJTs

Performances of some modern power BJT's in inductive turn-off are experimentally evaluated, by means of an unclamped non-destructive method. The different instabilities exhibited are classified and their influence on device performances is discussed both in clamped and unclamped applicationsAn “Instability Map” is proposed both as a synthetic picture which eases comparison of reverse-bias performances of devices having different ratings, and as an investigation tool for linking device behaviour to its physical features.It results that RBSOA performances are not just related to lateral dimensions of the emitter, but also to metallization lay-out of the chip, which evidently influences current distribution among cells.Finally, stray elements of testing circuit which affect results of RBSOA measurements are investigated, and some suggestions are proposed in order to let measurement results become independent of testing circuit.     

Reverse bias instabilities in bipolar power transistors withcellular layout

The different instabilities exhibited by power BJTs during inductive turn-off are classified, and then studied theoretically, by means of two-dimensional (2-D) simulator in which the device is simulated within a realistic external circuit, and experimentally, by means of a nondestructive method. It is shown that many instabilities originate by an interaction between electric field and charge within a single cell, which causes transit time oscillation phenomena. The role of the stray capacitance of the circuit in favoring these instabilities is described. Other kinds of instability cannot be understood by studying a single cell but rather require accounting for the interactions between cells. Finally, an “instability map” is used as a synthetic picture of the device behavior which ensures an easy way to link device behavior with its physical features     

Boosting Direct X‐Ray Detection in Organic Thin Films by Small Molecules Tailoring

The attention focused on the application of organic electronics for the detection of ionizing radiation is rapidly growing among the international scientific community, due to the great potential of organic technology to enable large‐area conformable sensor panels. However, high‐energy photon absorption is challenging as organic materials are constituted of atoms with low atomic numbers. Here it is reported how, by synthesizing new solution‐processable organic molecules derived from 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) and 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene, with Ge‐substitution in place of the Si atoms to increase the material atomic number, it is possible to boost the X‐ray detection performance of organic thin films on flexible plastic substrates. Bis(triisopropylgermylethynyl)‐pentacene based flexible organic thin film transistors show high electrical performance with higher mobility (0.4 cm² V^?1 s^?1) and enhanced X‐ray sensitivity, up to 9.0 × 10⁵ µC Gy^?1 cm^?3, with respect to TIPS‐pentacene‐based detectors. Moreover, similar results are obtained for 5,11‐bis(triethylgermylethynyl)anthradithiophene devices, confirming that the proposed strategy, that is, increasing the atomic number of organic molecules by chemical tailoring to improve X‐ray sensitivity, can be generalized to organic thin film detectors, combining high X‐ray absorption, mechanical flexibility, and large‐area processing.