Protective circuit for protecting load against excessive input voltage

Claim 2

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being permanently shorted to said source of said depletion mode MOSFET, said depletion mode MOSFET having a size and a pinch-off voltage such that said depletion mode MOSFET operates in a linear region when said input voltage is at a normal level and becomes saturated when said input voltage reaches an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 3

The arrangement of claim 1 further comprising a diode, said diode being connected to said source of said said depletion mode MOSFET such that said diode experiences breakdown when said input voltage reaches said excessive level.

Claim 4

The arrangement of claim 1 wherein said depletion mode MOSFET and said load are adapted such that said depletion mode MOSFET is operated near a saturation current of said depletion mode MOSFET when said input voltage is at a normal operating level.

Claim 5

The arrangement of claim 1 further comprising a diode connected in series with said depletion mode MOSFET, said diode being connected so as to block a reverse flow of current through said load.

Claim 6

The arrangement of claim 1 contained within a motor vehicle, said source of an input voltage comprising a generator and a battery, said load comprising a semiconductor component within said motor vehicle, said protective circuit functioning to protect said semiconductor component from a load dump or inductive voltage spike.

Claim 7

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being connected to switching circuitry, said switching circuitry connecting said gate of said depletion mode MOSFET to ground when said input voltage reaches an excessive value such that said depletion mode MOSFET becomes saturated and thereby protects said load from said excessive current.

Claim 8

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being connected to switching circuitry, said switching circuitry connecting said gate of said depletion mode MOSFET to ground when said input voltage reaches an excessive value such that said depletion mode MOSFET becomes saturated and thereby protects said load from said excessive current.

Claim 9

The arrangement of claim 5 further comprising a diode, said diode being connected to said source of said depletion mode MOSFET such that said diode experiences breakdown when said input voltage reaches said excessive level.

Claim 10

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input: of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being permanently connected to ground, said depletion mode MOSFET having a size and a pinch-off voltage such that said depletion mode MOSFET operates in a linear region when said input voltage is at a normal level and becomes saturated when said input voltage reaches an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 11

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input: of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being permanently connected to ground, said depletion mode MOSFET having a size and a pinch-off voltage such that said depletion mode MOSFET operates in a linear region when said input voltage is at a normal level and becomes saturated when said input voltage reaches an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 12

The arrangement of claim 8 contained within a motor vehicle, said source of an input voltage comprising a generator and a battery, said load comprising a semiconductor component within said motor vehicle, said protective circuit functioning to protect said semiconductor component from a load dump or inductive voltage spike.

Claim 13

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being permanently connected to a constant reference voltage at a level between a voltage at said source of said depletion mode MOSFET and ground, said depletion mode MOSFET having a size and a pinch-off voltage such that said depletion mode MOSFET operates in a linear region when said input voltage is at a normal level and becomes saturated when said input voltage reaches an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 14

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being permanently connected to a constant reference voltage at a level between a voltage at said source of said depletion mode MOSFET and ground, said depletion mode MOSFET having a size and a pinch-off voltage such that said depletion mode MOSFET operates in a linear region when said input voltage is at a normal level and becomes saturated when said input voltage reaches an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 15

The arrangement of claim 10 further comprising a diode, said diode being connected to said source of said depletion mode MOSFET such that said diode experiences breakdown when said input voltage reaches said excessive level.

Claim 16

The arrangement of claim 10 further comprising a zener diode and a resistor connected in series, said gate being connected to a common node between said zener diode and said resistor.

Claim 17

The arrangement of claim 10 contained within a motor vehicle, said source of an input voltage comprising a generator and a battery, said load comprising a semiconductor component within said motor vehicle, said protective circuit functioning to protect said semiconductor component from a load dump or inductive voltage spike.

Claim 18

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being connected to switching circuitry, said switching circuitry connecting said gate to a first voltage so as to cause said depletion mode MOSFET to operate in a linear region when said input voltage is at a normal level, said switching circuitry connecting said gate to a second voltage so as to cause said depletion mode MOSFET to operate become saturated when said input voltage is at an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 19

An arrangement including a source of an input voltage and a load to be protected from excessive current, said arrangement further including a protective circuit connected between said source and said load, said protective circuit comprising a depletion mode MOSFET, a drain of said depletion mode MOSFET being coupled to an input of said protective circuit and a source of said depletion mode MOSFET being coupled to an output of said protective circuit, a gate of said depletion mode MOSFET being connected to switching circuitry, said switching circuitry connecting said gate to a first voltage so as to cause said depletion mode MOSFET to operate in a linear region when said input voltage is at a normal level, said switching circuitry connecting said gate to a second voltage so as to cause said depletion mode MOSFET to operate become saturated when said input voltage is at an excessive level, said depletion mode MOSFET thereby protecting said load from said excessive current.

Claim 20

The arrangement of claim 14 wherein said switching circuitry connects said gate of said depletion mode MOSFET to a voltage below a voltage at a source of said MOSFET when said input voltage reaches said excessive level.

Claim 21

The arrangement of claim 15 wherein said switching circuitry comprises a comparator, an input of said comparator being connected to a reference voltage, a signal at an output of said comparator being used to provide a voltage at said gate of said depletion mode MOSFET.

Claim 22

The arrangement of claim 16 wherein said gate of said depletion mode MOSFET is connected to ground when said input voltage reaches said excessive level.

Claim 23

The arrangement of claim 16 wherein said gate of said depletion mode MOSFET is connected to a second reference voltage when said input voltage reaches said excessive level, said second reference voltage being at a level between a voltage at said source of said depletion mode MOSFET and ground.

Claim 24

The arrangement of claim 14 wherein said switching circuitry comprises a differential amplifier, a signal at an output of said differential amplifier being used to provide a voltage at said gate of said depletion mode MOSFET.

Claim 25

The arrangement of claim 19 wherein a first input of said differential amplifier is connected to said source and a second input of said differential amplifier is connected to a reference voltage, said reference voltage being at a level ground and a voltage at a source of said depletion mode MOSFET when said input voltage is at a normal level.

Claim 26

The arrangement of claim 14 contained within a motor vehicle, said source of an input voltage comprising a generator and a battery, said load comprising a semiconductor component within said motor vehicle, said protective circuit functioning to protect said semiconductor component from a load dump or inductive voltage spike.

Claim 29

The method of claim 22 wherein the step of driving said gate comprises the step of biasing said gate at a voltage equal to a voltage at a source of said depletion mode MOSFET.

Claim 30

The method of claim 22 wherein the step of driving said gate comprises the step of biasing said gate at a voltage equal to ground.

Claim 31

The method of claim 22 wherein the step of driving said gate comprises the step of biasing said gate at a voltage equal to a reference voltage at a level between a voltage at a source of said depletion mode MOSFET and ground.

Claim 32

The method of claim 22 wherein the step of driving said gate comprises the step of biasing said gate at a first voltage when said input voltage is at said normal level and biasing said gate at a second voltage when said input voltage is at said predetermined level above said normal level.

Claim 33

The method of claim 26 wherein said first voltage is greater than said second voltage.

Claim 34

The method of claim 26 wherein said first voltage is equal to a voltage at a source of said depletion mode MOSFET.

Claim 35

The method of claim 26 wherein said second voltage is equal to ground.

Claim 36

The method of claim 26 wherein said second voltage is at a level between a voltage at a source of said depletion mode MOSFET and ground.