Snubber circuit R2C2, as shown, might be necessary since Rl and Cl are tailored for optimized triggering and not for dV!dt protection. Fiber-optic pairs can be used with discrete SCRs to switch thousands of volts. A photon coupler with a transistor output will limit the trigger-pulse amplitude and rise time because of CTR and saturation effects.
Using the HllCl, the rise time of the input pulse to the photon coupler is not critical, and its amplitude is limited only by lite HllCl turn-on sensitivity. The load can also be connected to the cathode as illustrated in Fig. 67-3B.