At turn off the current commutes into the snubber via
storage capacitor Cgl until voltage on capacitor C,l
exceeds the clamp voltage of zener diode D,. This
triggers thyristor SCRa1 to conduct and divert snubber
current trough the thyristor. The alternative direction
current commutes into snubber via diode Dll. When
control signal is applied, the storage capacitor
provides energy to turn on SCR. To minimize storage
capacitor voltage drop,the signal from diagnostic
resistor is used for economized gating. The initial
charge of the capacitor C,, is provided in a similar
manner by ac voltage across the SCR, and delay in
the gating SCR when voltage is applied.