the high voltage input 10 can be controlled by the gate voltage of protection fet 30 which means the lower the gate voltage is the earlier the transistor turns off whilst the input voltage is rising 3 the digital u201c low voltage u201d input of the schmitt trigger 70 sees the input voltages at the high voltage input port 10 as long as they don 39 t exceed said input range when the maximum of said range is exceeded and the transistor is turned off this input needs to stick at a defined level which then indicates that the input level is high this level is provided by the pull up circuit 40 4 the enable circuit 60 switches the pull up circuit 40 and the schmitt trigger 70 on or off the gate voltage can either be controlled separately by block gate voltage 20 as in the schematic diagram fig1 in order to switch off the transistor 30 when the low voltage circuit is disabled or the gate voltage can be set up by controlling it via a combined enable and control block 5 the u201c low voltage u201d input follows the high voltage input for voltages below values u2018 gate voltage minus threshold voltage u2019 v gate u2212 v th the digital u201c.