Dissipation in solid-state devices - the magic of I1+N

The current capacity of a solid-state device, as ordinarily rated, varies widely depending on the current waveform, duty cycle, case temperature, etc. The underlying junction temperature limits should, however, be invariant. This paper presents a new analytical approach to the determination of dissipation and junction temperature in solid-state diodes and thyristors when subjected to either repetitive or surge currents of arbitrary waveforms. Both the on-state voltage and the transient thermal impedance are represented by power-law functions which can be closely fitted to the actual characteristics. Relationships are derived which permit the arbitrary current waveforms to be replaced by equivalent constant currents for which the temperature rise is easily calculated. The adoption of ratings based on this approach would permit simplification of the device manufacturer´s data sheet, greater generality in dealing with non-standard waveforms, and efficient utilization of computer analysis.