thinQ!TM Silicon Carbide Schottky Diodes: An SMPS Circuit Designer’s Dream Comes True!

T H E D R I V I N G M A R K E T F O R C E F O R A U N I P O L A R D I O D E W I T H H I G H B L O C K I N G V O L T A G E System miniaturization—the reduction of system size and weight—is a significant trend in electronics. Miniaturization is primarily, but not exclusively, being driven by the increasing number of portable applications. In most portable electronic devices, the dimensions and weight of the power supply make it the predominant part of the whole system. For example, in a typical portable computer, the power supply accounts for more than 10% of the total weight of the system. As a result, all manufacturers of Switch Mode Power Supplies (SMPS) have defined roadmaps to increase the power density in their products. The two major approaches to implementing these roadmaps are: • Reducing the size of passive components (by increasing the switching frequency and/or reducing the size of EMI filters through low noise generation) • Reducing the power losses and the corresponding cooling effort (heat sink and/or fan) To achieve these goals, the main semiconductor power components must achieve a significant reduction of switching power losses. For this reason, unipolar semiconductors such as MOSFETs and Schottky barrier diodes are replacing bipolar devices. The beauty of unipolarity is the absence of stored charge carriers and, therefore, theoretically instantaneous switching transients limited only by small parasitic capacitances. Power MOSFETs, such as CoolMOSTM & OptiMOSTM, can be found with a wide range of blocking voltage from 20 V to 1000 V. On the other hand, today’s Schottky barrier diodes have a maximum blocking voltage of 250 V due to the characteristics of the Silicon (Si) or Gallium Arsenide (GaAs) base material. The main reasons for this limitation are: • Very high leakage currents, especially at higher temperatures, because the reverse losses are comparable to the forward losses • Strong increases in the area specific onresistance Ron, A with breakdown voltage Vbr 2.5 • Increases of the chip also increases the reverse losses The input stage of an off-line SMPS usually requires devices rated in the range of 500 – 600 V. Thus, a strong and unsatisfied need exists for Schottky barrier diodes beyond the blocking capabilities of established semiconductors such as Si and GaAs.