Sampat Shekhawat

IGBT behavior during desat detection and short circuit fault protection

A common fault condition in motor drive applications involves an IGBT turning on into a short-circuit. If the only impedance is the cable inductance to a shorted motor winding, the current through the device ramps up very rapidly until it saturates, forcing the IGBT voltage to rise to the DC clamp. After fault detection, depending on the point at which the fast turn-off pulse is applied, very different levels of hole current can flow under the n/sup +/ source region, making this an important factor in the successful containment of the fault current. We present experimental observations showing that IGBT failure under short-circuit conditions is dependent on where the turn-off pulse is applied. The physics of this behavior is explained using numerical mixed-mode simulations. A practical two step gate waveform is studied for avoidance of device failure under short-circuit conditions, and is experimentally demonstrated.

Application specific 1200V planar and trench IGBTs

We compare planar and trench non-punch through (NPT) insulated gate bipolar transistors (IGBT) static and dynamic characteristics and evaluate them for motor drive, UPS, IH (induction heating) and switched mode power supply applications. The power supply market is mostly driven by high speed power devices and is presently dominated by MOSFET. The uninterruptible power supply (UPS) IGBTs need moderately high speed switching where as motor drive applications need low conduction loss and moderate switching speed devices. Some of these applications need good short circuit withstand time (SCWT). The planar IGBT has more SCWT and avalanche capability and is better suited for motor control. On the other hand, trench IGBT has better tradeoff curve and hence is a good choice for power supplies and IH markets. These new high speed NPT IGBTs can become cost effective for applications such as UPS, motor drive, IH as well as SMPS market by reducing overall loss over other 1200V IGBTs and regular 1000-1200 volts MOSFETs. By using these IGBTs, the efficiency can be improved or other trade off such as cost reduction, size reduction or increase in power density may be implemented. The new NPT IGBTs reduce both the switching and conduction losses over other 1200V IGBTs and MOSFETs. The turn-off switching loss was reduced by 40-60% compared to previous generation IGBTs and the conduction loss was reduced drastically compared to MOSFETs and IGBTs, especially at high junction temperature. NPT2 planar IGBT offers best of both worlds - lower cost and better performance

A 600V quick punch through (QPT) IGBT design concept for reducing EMI

Punch Through IGBTs inherently generate more EMI than their MOSFET counter part. This results from the nature of the IGBT being a two carrier device and the switching characteristics being controlled by the gain of the p-n-p bipolar. The EMI is a direct result of the abrupt turn-off di/dt. In this paper, a novel IGBT, the QPT, that enables the PT IGBT to switch similar to a MOSFET is presented and analyzed. This is achieved by designing the PT IGBT with a thinner lower concentration drift region. This allows the depletion layer to punch through to the buffer at a lower voltage. The capacitances of the QPT are optimized so that the channel remains open until the collector voltage reaches the bus voltage. This provides the ability to control and thereby minimize the turn-off di/dt.