Power Losses and Current Distribution Studies by Infrared Thermal Imaging in Soft- and Hard-Switched IGBTs under Resonant Load

A test bench is proposed to study, at die-level, the power losses and current distribution in power devices. It is based on an infrared camera and a flexible half-bridge resonant inverter with a tunable resonance frequency f res . With this setup, the die surface temperature is acquired in steady state, while the device is under real operation. The power losses are derived from the temperature mean value averaged, first, over a few switching cycles and, then, across the die surface. By contrast, the current distribution is inferred from the spectral component of the surface thermal map at the switching frequency (f Sw ). As a proof of concept, two case studies are reported considering 650 V-40 A insulated gate bipolar transistors (IGBTs) soft- and hard-switched within and outside the zero voltage switching condition. First, the power losses are analyzed under switching conditions representative of domestic induction heating applications (f res = 29.6 kHz) at f Sw = 40 kHz and f Sw = 20 kHz. Second, the power losses and local current distribution are investigated when f res = 9.25 kHz at f Sw ranged from 8.91 to 9.51 kHz. Such results are assessed with power losses electrical measurements and simulations, obtaining a satisfactory agreement. Moreover, hot spots are identified as current crowding points at f Sw , whose location is fixed by the bonding wires attachment to the die and the device edge termination. As main benefits of this technique, a higher spatial resolution is achieved and problems related with noisy electrical measurements resulting from the insertion of the used probes or transducers, power circuit stray elements, or device packaging parasitics are avoided.