10.1. Forward Drop 131
10.2. Forward Drop
SCRs have a nonlinear forward drop that is usually the major determi-
nant of the allowable load current in a circuit. The rated currents often
can be obtained from a series of curves most vendors show for various
phaseback angles. If the operating conditions do not correspond with
any published curves, the losses must be calculated from the current
waveform and the forward drop. A given SCR in a three-phase bridge
conducts only about 120°, neglecting commutation, per cycle. It is
important to calculate the power from the integrated V I product using
the actual current waveform. This power can then be divided by three
to get the average value over the cycle. The loss power cannot be
determined by using the average ...