Thermal diagnostics of high power electrical and optical device time to failure

The authors discuss an optoelectronic system capable of providing information on the instantaneous spatially averaged junction temperature of high-power devices such as GTO (gate turn-off thyristors) and IGBTs (insulated-gate bipolar transistors) and high-power semiconductor lasers. The potential applications of such a system are threefold: to provide real-time information on the junction temperatures for control purposes, to use the information pertaining to the device temperature for purposes of understanding the mechanism for device failure, and to specify power device ratings. The key features of this system are a micromanipulated fiber cable, a collimator, an acoustooptic modulator, two cooled InSb detectors with associated narrow-band filters, a temperature sensor, an electronic processing unit, a thermoelectric and thermomagnetic cascaded cooling unit, and a switched mode power supply. Major design issues such as the reduction in 1/f noise and high bandwidth operation were addressed by using an acoustooptic modulator. The detectors were operated without bias in order to minimize the noise. The minimum internal noise was controlled by lowering the detector temperature until the noise level was background-limited