US 7,480,126 B2Granted

Protection and voltage monitoring circuit

AssigneeNational Instruments Corporation

InventorsRaffaele Cetrulo, Mark Whittington

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Abstract

A protection and voltage monitoring circuit that may provide the functionality of a diode without the typical large voltage drop and power dissipation. The protection and voltage monitoring circuit may include a first MOSFET, a second MOSFET, a first resistor, an input terminal, an output terminal, a diode, a BJT current source, and a voltage monitoring circuit. The BJT current source may limit a gate-to-source voltage of the two MOSFETs to a predetermined voltage that is less than a maximum allowed voltage by controlling a current flow through the first resistor to prevent damage to the MOSFETs. The voltage monitoring circuit may determine whether an external voltage is within an allowable range of voltages. If the external voltage is outside the predetermined voltage range, the voltage monitoring circuit turns off the BJT current source to block the external voltage from the output terminal of the protection and voltage monitoring circuit.

Claims23

Dependent claims

A protection circuit comprising:

an output terminal;
an input terminal operable to receive an external voltage;
a first transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the first transistor is coupled to the input terminal of the protection circuit;
a second transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the second transistor is coupled to the output terminal of the protection circuit, the gate terminal of the second transistor is coupled to the gate terminal of the first transistor, and the source terminal of the second transistor is coupled to the source terminal of the first transistor;
a first resistor coupled between a junction of the source terminals of the first and second transistors and a junction of the gate terminals of the first and second transistors;
a current source coupled to the junction of the gate terminals of the first and second transistors and to the first resistor to limit a gate-to-source voltage of the first and second transistors to a predetermined voltage value that is less than a maximum allowed voltage value;
and
a voltage monitoring circuit coupled to the current source, wherein the voltage monitoring circuit includes:
a third transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the third transistor is coupled to the current source;
a fourth transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the fourth transistor is coupled to the source terminal of the third transistor, wherein the source terminal of the fourth transistor is coupled to ground;
and
a comparator circuit coupled to the gate terminal of the third and fourth transistors, wherein the comparator circuit is operable to determine whether the external voltage is within a predetermined voltage range.

9 more elements

A measurement device comprising:

a power supply;
and
a protection circuit including:
an input terminal operable to receive an external voltage;
an output terminal coupled to the power supply;
a first transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the first transistor is coupled to the input terminal of the protection circuit;
a second transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the second transistor is coupled to the output terminal of the protection circuit, the gate terminal of the second transistor is coupled to the gate terminal of the first transistor, and the source terminal of the second transistor is coupled to the source terminal of the first transistor;
a first resistor coupled between a junction of the source terminals of the first and second transistors and a junction of the gate terminals of the first and second transistors;
a current source coupled to the junction of the gate terminals of the first and second transistors and to the first resistor to limit a gate-to-source voltage of the first and second transistors to a predetermined voltage value that is less than a maximum allowed voltage value;
and
a voltage monitoring circuit coupled to the current source, wherein the voltage monitoring circuit includes:
a third transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the third transistor is coupled to the current source;
a fourth transistor including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the fourth transistor is coupled to the source terminal of the third transistor, wherein the source terminal of the fourth transistor is coupled to ground;
and
a comparator circuit coupled to the gate terminal of the third and fourth transistors, wherein the comparator circuit is operable to determine whether the external voltage is within a predetermined voltage range.

12 more elements

A protection circuit comprising:

an output terminal;
an input terminal operable to receive an external voltage;
a first MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the first MOSFET is coupled to the input terminal of the protection circuit;
a second MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the second MOSFET is coupled to the output terminal of the protection circuit, the gate terminal of the second MOSFET is coupled to the gate terminal of the first MOSFET, and the source terminal of the second MOSFET is coupled to the source terminal of the first MOSFET;
a first resistor coupled between a junction of the source terminals of the first and second MOSFETs and a junction of the gate terminals of the first and second MOSFETs;
a current source coupled to the junction of the gate terminals of the first and second MOSFETs and to the first resistor, wherein the current source is operable to limit a gate-to-source voltage of the first and second MOSFETs to a predetermined voltage value that is less than a maximum allowed voltage value, wherein the current source includes:
a first bipolar junction transistor (BJT) including a base terminal, an emitter terminal, and a collector terminal, wherein the collector terminal of the first BJT is coupled to the junction of the gate terminals of the first and second MOSFETs and to the first resistor;
and
a second BJT including a base terminal, an emitter terminal, and a collector terminal, wherein the collector terminal of the second BJT is coupled to a junction of the base terminal of the first BJT and a second resistor, wherein the second resistor is coupled to a power supply terminal, wherein the base terminal of the second BJT is coupled to a junction of the emitter terminal of the first BJT and a third resistor, and wherein the emitter terminal of the second BJT is coupled to the third resistor;
and
a voltage monitoring circuit coupled to the current source, wherein the voltage monitoring circuit includes:
a third MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the third MOSFET is coupled to a junction of the emitter terminal of the second BJT and the third resistor;
a fourth MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the fourth MOSFET is coupled to the source terminal of the third MOSFET, wherein the source terminal of the fourth MOSFET is coupled to ground;
and
a comparator circuit coupled to the gate terminal of the third and fourth MOSFETs, wherein the comparator circuit is operable to determine whether the external voltage is within a predetermined voltage range.

12 more elements

A measurement device comprising:

a power supply;
and
a protection circuit including:
an input terminal operable to receive an external voltage;
an output terminal coupled to the power supply;
a first MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the first MOSFET is coupled to the input terminal of the protection circuit;
a second MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the second MOSFET is coupled to the output terminal of the protection circuit, the gate terminal of the second MOSFET is coupled to the gate terminal of the first MOSFET, and the source terminal of the second MOSFET is coupled to the source terminal of the first MOSFET;
a first resistor coupled between a junction of the source terminals of the first and second MOSFETs and a junction of the gate terminals of the first and second MOSFETs;
a current source coupled to the junction of the gate terminals of the first and second MOSFETs and to the first resistor, wherein the current source is operable to limit a gate-to-source voltage of the first and second MOSFETs to a predetermined voltage value that is less than a maximum allowed voltage value, wherein the current source includes:
a first bipolar junction transistor (BJT) including a base terminal, an emitter terminal, and a collector terminal, wherein the collector terminal of the first BJT is coupled to the junction of the gate terminals of the first and second MOSFETs and to the first resistor;
and
a second BJT including a base terminal, an emitter terminal, and a collector terminal, wherein the collector terminal of the second BJT is coupled to a junction of the base terminal of the first BJT and a second resistor, wherein the second resistor is coupled to a power supply terminal, wherein the base terminal of the second BJT is coupled to a junction of the emitter terminal of the first BJT and a third resistor, and wherein the emitter terminal of the second BJT is coupled to the third resistor;
and
a voltage monitoring circuit coupled to the current source, wherein the voltage monitoring circuit includes:
a third MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the third MOSFET is coupled to a junction of the emitter terminal of the second BJT and the third resistor;
a fourth MOSFET including a gate terminal, a drain terminal, and a source terminal, wherein the drain terminal of the fourth MOSFET is coupled to the source terminal of the third MOSFET, wherein the source terminal of the fourth MOSFET is coupled to ground;
and
a comparator circuit coupled to the gate terminal of the third and fourth MOSFETs, wherein the comparator circuit is operable to determine whether the external voltage is within a predetermined voltage range.

15 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/115,773Filed 27 Apr 2005
Published: US 2006/0245133 A12 Nov 2006
Granted: 20 Jan 2009
Term ends: Not estimatedThe source records don’t support an estimate.

Classification6 codes

H02H 3/207
Responsive to excess voltage: also responsive to under-voltage
H02H 3/202
Responsive to excess voltage: for DC systems
H03K 17/0822
By feedback from the output to the control circuit: in field-effect transistor switches
H03K 17/6874
The output circuit comprising more than one controlled field-effect transistor: in a symmetrical configuration