Protective, bi-level drive for FET's

Claim 2

In an electronic circuit that uses an FET to supply current to a load, and wherein the FET has a drain electrode, a gate electrode and a source electrode, a method for protectively driving the FET, comprising: (a) generating, and applying to the gate electrode, a signal that has a first, relatively low, test level followed by a second, relatively higher operating level, the magnitude and the duration of the test level being selected to produce a non-destructive drain current in the FET irrespective of the impedance of the load, and the operating level being selected to produce a larger drain current whose level is appropriate for driving the load; (b) measuring the FET's drain-to-source potential at least while the test potential is being applied to the gate electrode; (c) turning the FET off when the measured value of the drain-to-source potential is high enough to indicate an abnormal load condition; and (d) allowing the FET turn on in response to the control signal's operating level when the value of the measured drain-to-source potential is indicative of a normal load condition.

Claim 3

A method as set forth in claim 1 further including: holding the FET on while the test level is being applied to the FET's gate electrode, irrespective of previously measured values of the FET's drain-to-source potential.

Claim 4

In an electronic circuit that uses an FET to supply current to a load, and wherein the FET has a drain electrode, a gate electrode and a source electrode, a method for cyclically driving the FET while also prohibiting destructively high drain currents without the need for current sensing devices, the method comprising: (a) applying a periodic control signal to the FET's gate electrode, the control signal including at least: (a) a test interval during which the control signal is at a test level selected to produce a predetermined, non-destructive level of drain current; and (b) an operating interval during which the control signal is at relatively higher operating level selected to produce a larger drain current; (b) holding the FET on during the test interval; (c) measuring the FET's drain-to-source potential during the entire duration of the control signal; (d) comparing the measured potential to a given reference potential; (e) turning the FET off when the measured value of the drain-to-source potential is higher than the given reference level; and (f) repeating steps (a) through (e) for each cycle of operation.

Claim 5

In an electronic circuit that uses an FET to supply current to a load, and wherein the FET has a drain electrode, a gate electrode and a source electrode, a method for cyclically driving the FET while also prohibiting destructively high drain currents without the need for current sensing devices, the method comprising: (a) applying a periodic control signal to the FET's gate electrode, the control signal including at least: (a) a test interval during which the control signal is at a test level selected to produce a predetermined, non-destructive level of drain current; and (b) an operating interval during which the control signal is at relatively higher operating level selected to produce a larger drain current; (b) holding the FET on during the test interval; (c) measuring the FET's drain-to-source potential during the entire duration of the control signal; (d) comparing the measured potential to a given reference potential; (e) turning the FET off when the measured value of the drain-to-source potential is higher than the given reference level; and (f) repeating steps (a) through (e) for each cycle of operation.