US 6,807,040 B2 · Over-current protection circuit and method

Abstract

Over-current protection is accomplished in an output transistor (MP) of an electronic circuit wherein an input signal (Vgatedrive) Is Applying to a first conductor (19) coupled to a gate of the output transistor to cause an output current (Iout) to flow through the output transistor and an output terminal (11) of the electronic circuit. A limit voltage (VLIMIT) who is applied to an input (21) of a voltage clamping circuit (18) to cause a clamping current to flow in the first conductor (19) as needed to prevent the magnitude of the input signal (Vgatedrive) from being less than the magnitude of the limit voltage (VLIMIT) so that the output current (Iout) is limited to a maximum current limit determined by the limit voltage (VLIMIT). A control signal (ILIMIT/n) is applied to an input of a current-to-voltage conversion circuit (20) to cause the current-to-voltage conversion circuit to produce the limit voltage (VLIMIT), which is applied to an emitter of a first transistor (Q1) having a collector in base connected to a bias current source (I1). The resulting voltage on a base of the first transistor is applied to a base of a second transistor (Q2), and the input signal (Vgatedrive) is applied to the first conductor (19).

Claims19

Dependent claims

An electronic circuit including an over-current protection circuit therein, the over-current protection circuit comprising:

(a) an output transistor having a drain coupled to an output terminal of the electronic circuit, a gate directly coupled a first conductor to receive an input voltage, and a source coupled to a supply voltage conductor;
(b) a control circuit for producing a limit voltage, the control circuit having a first terminal coupled to a second conductor for conducting a control signal and a second terminal coupled to a third conductor for conducting the limit voltage;
(c) a voltage clamping circuit having a first terminal coupled to the third conductor to receive the limit voltage and a second terminal coupled to the first conductor to receive the input voltage;
and
(d) the control circuit and the voltage clamp circuit coacting to limit a current in the output transistor to a maximum value determined by the control signal.

2 more elements

An electronic circuit including an over-current protection circuit therein, the over-current protection circuit comprising:

(a) an output transistor having a drain coupled to an output terminal of the electronic circuit, a gate coupled a first conductor to receive an input voltage, and a source coupled to a supply voltage conductor;
(b) a control circuit for producing a limit voltage, the control circuit having a first terminal coupled to a second conductor for conducting a control signal and a second terminal coupled to a third conductor for conducting the limit voltage:
(C) a voltage clamping circuit having a first terminal coupled to the third conductor to receive the limit voltage and a second terminal coupled to the first conductor to receive the input voltage;
(d) the control circuit and the voltage clamp circuit coacting to electrically isolate the first conductor from the third conductor when the magnitude of the input voltage exceeds the magnitude of the limit voltage and to prevent a current in the output transistor from Increasing enough to exceed a maximum current limit determined by the control signal when the magnitude of the input voltage Is less than the magnitude of the limit voltage;
(e) wherein the voltage clamping circuit includes a first transistor having an emitter coupled to the third conductor and a base and collector both coupled to a bias current source, a second transistor having a base coupled to the base and collector of the first transistor, an emitter coupled to the first conductor, a third transistor having an emitter coupled to the third conductor, a base coupled to the base and collector of the first transistor, and a collector coupled to a drain and gate of a fourth transistor having a source coupled to the supply voltage conductor, a fifth transistor having a source coupled to the supply voltage conductor, a gate coupled to the gate and drain of the fourth transistor, and a drain coupled to a collector of the second transistor, and a sixth transistor having a source coupled to the supply voltage conductor, a gate coupled to the collector of the second transistor, and a drain coupled to the first conductor
wherein the third, fourth, fifth, and sixth transistors coact to cause additional current to flow in the first conductor as needed to prevent the current in the output transistor from increasing enough to exceed a maximum current limit determined by the control signal when the magnitude of the input voltage is less than the magnitude of the limit voltage.

3 more elements

An electronic circuit including an over-current protection circuit therein, the over-current protection circuit comprising:

(a) an output transistor having a drain coupled to an output terminal of the electronic circuit, a gate coupled to receive an input voltage, and a source coupled to a supply voltage conductor;
(b) a current-to-voltage converter circuit for producing a limit voltage in response to a reference current, the current-to-voltage converter circuit having a first terminal for conducting the reference current, a second terminal for conducting the limit voltage, and a third terminal connected to the output terminal of the electronic circuit;
(c) a voltage clamping circuit having a first terminal coupled to the third conductor to receive the limit voltage and a second terminal coupled to the first conductor to receive the input voltage;
(d) the control circuit and the voltage clamp circuit coacting to electrically isolate the first conductor from the third conductor when the magnitude of the input voltage exceeds the magnitude of the limit voltage and to prevent a current in the output transistor from increasing enough to exceed a maximum current limit determined by the control signal when the magnitude of the input voltage is less than the magnitude of the limit voltage;
(e) wherein the voltage clamping circuit includes a first transistor having an emitter coupled to the third conductor and a base and collector both coupled to a bias current source, a second transistor having a base coupled to the base and collector of the first transistor, an emitter coupled to the first conductor, a third transistor having an emitter coupled to the third conductor, a base coupled to the base and collector of the first transistor, and a collector coupled to a drain and gate of a fourth transistor having a source coupled to the supply voltage conductor, a fifth transistor having a source coupled to the supply voltage conductor, a gate coupled to the gate and drain of the fourth transistor, and a drain coupled to a collector of the second transistor, and a sixth transistor having a source coupled to the supply voltage conductor, a gate coupled to the collector of the second transistor, and a drain coupled to the first conductor;
wherein the third, fourth, fifth, and sixth transistors coact to cause additional current to flow in the first conductor as needed to prevent the current in the output transistor from increasing enough to exceed a maximum current limit determined by the control signal when the magnitude of the input voltage is less than the magnitude of the limit voltage.

3 more elements

A method of providing over-current protection in an output transistor of an electronic circuit, comprising:

(a) applying an input signal to a first conductor coupled to a gate of the output transistor to cause an output current to flow through the output transistor and an output terminal of the electronic circuit;
(b) applying a limit voltage to an input of a voltage clamping circuit;
and
(c) operating the voltage damping circuit to cause a clamping current to flow in the first conductor as needed to prevent the input signal from having a value that is beyond a predetermined level relative to the limit voltage wherein the output current is prevented from having a value greater than a current limit determined by the limit voltage,
wherein step (b) includes applying the limit voltage to an emitter of a first transistor having a collector in base connected to a bias current source, and applying the resulting voltage on a base of the first transistor to a base of a second transistor, and step (a) includes applying the input signal to the first conductor.

2 more elements

Dependencies are inferred from the claim text.

Over-current protection circuit and method

Life of this patent

Over-current protection circuit and method

Life of this patent

Abstract

Claims19