Voltage regulator capable of enabling overcurrent protection in a state in which an output current is large
View Patent ↗Provided is a voltage regulator capable of enabling overcurrent protection in a state in which an output current is large even if an input/output voltage difference is small, without waiting until the output voltage decreases. A sense current that a sense transistor flows is detected by a differential amplifier circuit, and hence, in the state in which the input/output voltage difference is small and the output current is large, the overcurrent protection can be enabled even when the output voltage does not decrease. Further, a good fold-back characteristic can be obtained.
1. A voltage regulator, comprising:
a reference voltage circuit for outputting a reference voltage;
an output transistor;
a first differential amplifier circuit for amplifying and outputting a difference between the reference voltage and a divided voltage obtained by dividing a voltage output by the output transistor, to thereby control a gate of the output transistor; and
an overcurrent protection circuit for protecting the voltage regulator from an overcurrent of an output current of the output transistor,
wherein the overcurrent protection circuit comprises:
a sense transistor for sensing the output current;
a first transistor including a drain connected to a drain of the sense transistor;
a second differential amplifier circuit including an output terminal connected to a gate of the first transistor, an inverting input terminal connected to a source of the first transistor, and a non-inverting input terminal connected to a non-inverting input terminal of the first differential amplifier circuit;
a first resistor connected to the source of the first transistor; and
a control circuit for controlling the gate of the output transistor based on a current flowing through the sense transistor.
2. A voltage regulator according to claim 1 , wherein the control circuit comprises:
a second transistor including a gate and a drain which are connected to the drain of the sense transistor;
a third transistor which is current-mirror-connected to the second transistor;
a fourth transistor including a gate and a drain which are connected to a drain of the third transistor; and
a fifth transistor which is current-mirror-connected to the fourth transistor and includes a drain connected to the gate of the output transistor.
3. A voltage regulator according to claim 1 , wherein the control circuit comprises:
a third differential amplifier circuit including a non-inverting input terminal connected to the reference voltage circuit and an inverting input terminal connected to the drain of the sense transistor;
a second resistor connected to the inverting input terminal of the third differential amplifier circuit; and
a second transistor including a gate connected to an output terminal of the third differential amplifier circuit and a drain connected to the gate of the output transistor.