The MBGT: a thyristor with IGBT switching characteristics

The IGBT is the device of choice in many medium power applications such as industrial motor drives. The structure offers simple gate drive requirements and the ability to be paralleled, but suffers from a relatively high on-state voltage. Consequently, IGBT circuits are often inefficient and large losses must be dealt with. In comparison, MOS controlled thyristors offer a superior on-state performance by virtue of their latched operation. However, the limitations of the MCT means that the GTO remains the only available option in various applications. A device that builds on the proven success of the GTO and IGBT and employs similar processing technology represents an important advance in power electronics. Such a device can offer the advantages of a latched on state combined with the robust turn-off behaviour of an IGBT. To achieve this end, the MOS and bipolar gated thyristor (MBGT) has been developed. This device takes the best of both the IGBT and GTO characteristics, requiring dual gates to define its two modes of operation. In this paper the MBGT is described in detail and its behaviour is discussed with reference to experimental waveforms for a test structure. The performance of the MBGT is then compared to that of the equivalent GTO and IGBT by using the respective single modes of operation of the experimental structure. Consideration is given to the unique features of the MBGT and the optimisations possible which will make it the device of preference in many applications.