Switching regulator control circuit and switching regulator
View Patent ↗Provided is a switching regulator including an overload protection circuit, which has high accuracy even without requiring adjusting means in a test step. The switching regulator includes: a first triangle wave generation circuit for generating a first triangle wave which controls Duty of a PWM signal; and a second triangle wave generation circuit for generating a second triangle wave for overload detection, which has a crest value smaller than that of the first triangle wave. A ratio between the crest value of the first triangle wave and the crest value of the second triangle wave is set based on respective capacitances or constant currents thereof.
1. A switching regulator control circuit, comprising:
an error amplifying circuit for amplifying a difference voltage between a reference voltage and a divided voltage obtained by dividing an output voltage output from a switching regulator;
a first triangle wave generation circuit for outputting a first triangle wave;
a first comparator for comparing an output voltage of the error amplifying circuit and the first triangle wave;
a second triangle wave generation circuit, which has the same circuit structure as the first triangle wave generation circuit, for outputting a second triangle wave having a crest value smaller than a crest value of the first triangle wave;
a second comparator for comparing the output voltage of the error amplifying circuit and the second triangle wave; and
a determination circuit for detecting an overload state based on an output signal of the second comparator,
wherein a difference between the crest value of the first triangle wave and the crest value of the second triangle wave is set based on a characteristic ratio between a device corresponding to the first triangle wave generation circuit and a device corresponding to the second triangle wave generation circuit.
2. A switching regulator control circuit according to claim 1 , further comprising a rectangular wave oscillation circuit for outputting a rectangular wave,
wherein the first triangle wave generation circuit comprises:
a first capacitor;
a first constant current source for one of charging and discharging the first capacitor; and
first switching means, which is controlled by the rectangular wave, for one of discharging and charging the first capacitor, and
wherein the second triangle wave generation circuit comprises:
a second capacitor;
a second constant current source for one of charging and discharging the second capacitor; and
second switching means, which is controlled by the rectangular wave, for one of discharging and charging the second capacitor.
3. A switching regulator control circuit according to claim 2 , wherein a ratio between the crest value of the first triangle wave and the crest value of the second triangle wave is obtained based on a capacitance ratio between the first capacitor and the second capacitor.
4. A switching regulator control circuit according to claim 2 , wherein a ratio between the crest value of the first triangle wave and the crest value of the second triangle wave is obtained based on a current ratio between the first constant current source and the second constant current source.
5. A switching regulator, comprising:
an input terminal and an output terminal;
an output transistor, a coil, a rectifying device, and an output capacitor, which are provided between the input terminal and the output terminal;
a voltage dividing resistor for dividing a voltage of the output terminal; and
the switching regulator control circuit according to claim 1 , into which the voltage divided by the voltage dividing resistor is input, for controlling the output transistor so that the voltage of the output terminal is constant.