Some Rating and Application Considerations for Silicon Diodes

The dissipation in a silicon rectifier depends on the characteristics of the rectifier (threshold voltage and ohmic resistance) and the circuit constants (inductive, resistive, or capacitive load). Dissipations under these different conditions are calculated. The maximum permissible dissipation is limited by maximum junction temperature and thermal stability. The stability criterion depends on the thermal resistance, the reverse characteristic and its change with respect to temperature, the reverse voltage, and the circuit configuration. Derating curves are obtained, based on known variations of the reverse characteristics of silicon rectifiers with temperature and voltage. The maximum permissible transient dissipation depends on the total surge energy. The energy dissipated in the rectifier is high when the load capacitance is high and the external series resistance is low. A design embodying all the foregoing considerations is illustrated.