Patent ID: 8154320

Claim:
An apparatus for coupling a source of digital control signals to a load energized by a second voltage source, where said source of digital control signals and said second voltage source are connected to a common reference potential, said load being subject to temperature-dependent changes, said apparatus comprising; a depletion-mode first field-effect transistor including a controlled current path defining first and second electrodes and a control electrode coupled to said controlled current path, said control electrode being connected to said first electrode of said depletion-mode first field-effect transistor; a plurality of unidirectional current conducting devices connected in series to define a string, said string defining first and second ends, each of said unidirectional current conducting devices defining first and second terminals, and each being for conducting when said first terminal is positive with respect to said second terminal, said first terminal of one of said plurality of series-connected unidirectional current conducting devices at said first end of said string being connected to said first electrode of said depletion-mode first field-effect transistor; a resistor including a first end connected to said second terminal of one of said plurality of series-connected unidirectional current conducting devices at said second end of said string and also including a second terminal connected to said common reference potential; a first enhancement mode field-effect transistor including a controlled current path defining first and second electrodes and also including a control electrode coupled to said controlled current path, said control electrode of said first enhancement mode field effect transistor being connected to said first end of said resistor, said first electrode of said first enhancement mode field-effect transistor being connected to said common reference potential; and a conductive arrangement connecting said load in series with said second electrode of said controlled current path of said first enhancement mode field-effect transistor and to an energizing potential electrode of said second voltage source.