SCR controlled by the power bias

A composite dual SCR circuit that acts to protect the Vcc node as well as an I/O node or pin. The dual SCR uses the Vcc to control or program the triggering point of the SCR connected to an I/O node. When Vcc is low, the SCR protecting an I/O node triggers a few volts above ground, but when Vcc is high the trigger point of the SCR protecting the I/O node is much higher. The dual SCR incorporates added diffusions to an existing first SCR structure between the power node and the ground node thereby forming a second SCR. The first and second SCRs share a common cathode transistor. In one illustrative embodiment, only one SCR is constructed incorporating the Vcc to control the triggering of the SCR.