In some applications, VS is actually higher than the maximum voltage allowed by the datasheet for the protected circuit, but because the voltage is present for such a short time, the SIDACtor device will always win the race to breakdown. VS is influenced by the size and speed of the SIDACtor device, the rate of rise of the applied overvoltage event and, to a lesser degree, the source impedance of the overvoltage event. Because this more of a performance parameter than a device parameter, the exact conditions of the test circuit must be specified. Littlefuse uses a 100V/µS linear wavefront from a fairly high impedance source to define VS. VS will also increase slightly as the device’s temperature is increased.