The IL421x uses two discrete SCRs resulting in a commutating dv/dt of greater than 10KV/s. The use of a proprietary dv/dt clamp results in a static dv/dt of greater than 10KV/s. This clamp circuit has a MOSFET that is enhanced when high dv/dt spikes occur between MT1 and MT2 of the TRIAC. The FET clamps the base of the phototransistor when conducting, disabling the internal SCR predriver. The blocking voltage of up to 800 V permits control of off-line voltages up to 240 VAC, with a safety factor of more than two, and is sufficient for as much as 380 VAC. Current handling capability is up to 300 mA RMS, continuous at 25C.