Model 18TBP/TB solid state variacs incorporate exclusive design features to protect power semiconductor components against damage. "2 milli- second” fuses protect the solid state variac against short-circuit damage; an R-C snubber network protects the solid state variac against dv/dt failure; an integral heatsink chassis allows continuous operation in ambients to 50C with no derating.
Model 36TBP controls provide a full-wave rectified, infinitely variable DC output voltage from a single-phase AC input. Phase-angle control via power semiconductors varies the AC input voltage, which in turn is full-wave rectified. The result is the infinitely variable DC output. Because power semiconductors replace contacts and brushes to switch electric power without moving parts, there is no MTBF or life expectancy rating on these devices as long as they are operated within their stated ratings for current, voltage, and temperature.