Vishay has several uni-directional and bi-directional TVS series with various clamping voltages. Uni-directional TVS and XClampR® TVS can make asymmetrical clamping voltage protection as pictured here. Clamping voltage at positive surge voltage is the sum of the clamping voltages of XClampR TVS and conventional TVS. At negative surge voltage, the clamping voltage is XClampR TVS’s clamping voltage plus forward voltage of the uni-directional TVS. Bi-directional TVS and XClampR TVS can make symmetrical clamping characteristics at positive and negative voltage surges, and the clamping voltage is the sum of XClampR TVS and conventional TVS clamping voltages. The clamping current capability of both combinations is limited by the smaller side of the device.