Overcurrent protection circuit for controlling a gate of an output transistor based on an output current
View Patent ↗To provide an overcurrent protection circuit which prevents an excessive current from flowing to an output terminal for a long time, and a semiconductor device and a voltage regulator each equipped with the overcurrent protection circuit. An overcurrent protection circuit is configured to include a first transistor which allows a current proportional to an output current flowing through an output transistor to flow, a constant current circuit which allows a reference current to flow, a comparison circuit which compares the current flowing through the first transistor and the reference current, and a control circuit which controls a gate of the output transistor by a signal outputted from the comparison circuit.
1. An overcurrent protection circuit, comprising:
a first transistor which allows a current proportional to an output current flowing through an output transistor to flow;
a constant current circuit which allows a reference current to flow;
a comparison circuit which compares the current flowing through the first transistor and the reference current; and
a control circuit which controls a gate of the output transistor by a signal outputted from the comparison circuit, the control circuit connected to the constant current circuit and the output transistor,
wherein the control circuit is a current amplifier circuit which includes a fourth transistor having a gate and drain connected to the constant current circuit, and a fifth transistor having a gate connected to the gate of the fourth transistor, and a drain connected to the gate of the output transistor, and configures a current mirror;
wherein the control circuit controls a turn-off speed of the output transistor based on a magnitude of a current flowing through the fifth transistor.
2. The overcurrent protection circuit according to claim 1 , wherein the comparison circuit includes a second transistor having a gate and drain connected to a drain of the first transistor, and a third transistor having a gate connected to the gate of the second transistor and a drain connected to the constant current circuit, and configures a current mirror, and
wherein the comparison circuit compares the reference current and a current of the third transistor.
3. A semiconductor device, comprising:
an output transistor which outputs an input voltage to an output terminal;
a driving circuit which controls the operation of the output transistor; and
the overcurrent protection circuit according to claim 1 .
4. A voltage regulator, comprising:
an output transistor which outputs a predetermined output voltage to an output terminal;
an error amplifier circuit which amplifies and outputs a difference between a divided voltage obtained by dividing the output voltage and a reference voltage, and controls the gate of the output transistor; and
the overcurrent protection circuit according to claim 1 .
5. A voltage regulator, comprising:
an output transistor which outputs a predetermined output voltage to an output terminal;
an error amplifier circuit which amplifies and outputs a difference between a divided voltage obtained by dividing the output voltage and a reference voltage, and controls a gate of the output transistor; and
an overcurrent protection circuit,
wherein the overcurrent protection circuit includes a first transistor which allows a current proportional to an output current flowing through the output transistor to flow,
a constant current circuit which allows a reference current to flow;
a comparison circuit which compares the current flowing through the first transistor and the reference current, and
a control circuit which controls a bias current of the error amplifier circuit by a signal outputted from the comparison circuit, the control circuit connected to the constant current circuit and the output transistor,
wherein the control circuit is a current amplifier circuit which includes a fourth transistor having a gate and drain connected to the constant current circuit, and a fifth transistor having a gate connected to the gate of the fourth transistor, and a drain connected to the error amplifier circuit, and configures a current mirror;
wherein the control circuit controls a turn-off speed of the output transistor based on a magnitude of a current flowing through the fifth transistor.
6. The voltage regulator according to claim 5 , wherein the comparison circuit includes a second transistor having a gate and drain connected to a drain of the first transistor, and a third transistor having a gate connected to the gate of the second transistor and a drain connected to the constant current circuit, and configures a current mirror, and
wherein the comparison circuit compares the reference current and a current of the third transistor.