Control circuit for synchronous rectification type step-down switching regulator
AssigneeRohm Co., Ltd.
InventorsMasaru Sakai, Kiyotaka Umemoto
Life of this patent
Estimating the term…
Abstract
An output monitoring comparator outputs an ON signal when an output voltage becomes lower than a reference voltage. A pulse modulator generates a pulse signal at a predetermined level, an ON time-period from when the ON signal is outputted. A driver circuit alternately turns ON, after a dead time, a switching transistor and a synchronous rectification transistor, based on the pulse signal. A light load mode detector compares a switching voltage at a connection point of the switching transistor and the synchronous rectification transistor, and ground potential, and at timing at which the ON signal is outputted from the output monitoring comparator, when the switching voltage is higher than the ground potential, nullifies the ON signal.
Claims18
A control circuit of a synchronous rectification type of step-down switching regulator, the control circuit comprising:
- an output monitoring comparator which compares output voltage of the switching regulator and a reference voltage that is a target value thereof, and when the output voltage goes lower than the reference voltage, outputs an ON signal;
- a pulse modulator which generates a pulse signal which goes to a predetermined level in a predetermined ON time from when the ON signal was outputted from the output monitoring comparator;
- a driver circuit which generates a first and a second control signal based on the pulse signal outputted from the pulse modulator, and alternately turns ON a switching transistor by the first control signal and a synchronous rectification transistor by the second control signal;
- and
- a light load mode detector which receives a switching voltage occurring at a connection point of the switching transistor and the synchronous rectification transistor and a predetermined threshold voltage, compares the switching voltage with the predetermined threshold voltage, and at timing at which the ON signal is outputted from the output monitoring comparator, when the switching voltage is higher than the threshold voltage, nullifies the ON signal, wherein the light load mode detector, at timing at which the second control signal is inputted and
- the ON signal is outputted from the output monitoring comparator, when the switching voltage is higher than the threshold voltage, delays and outputs the second control signal to the pulse modulator;
- and
- the pulse modulator generates the pulse signal based on a result of a logical operation on the second control signal that is delayed and the ON signal.
A control circuit of a synchronous rectification type of step-down switching regulator, the control circuit comprising
- an output monitoring comparator which compares output voltage of the switching regular and a reference voltage that is a target value thereof and when the out voltage goes lower than the reference voltage, outputs an ON signal;
- a pulse modulator which generates a pulse signal which goes to a predetermined level in a predetermined ON time from when the ON signal was outputted from the output monitoring comparator;
- a driver circuit which generates a first and a second control signal based on the pulse signal outputted from the pulse modulator, and alternately turns ON a switching transistor by the first control signal and a synchronous rectification transistor by the second control signal;
- and
- a light load mode detector which receives a switching voltage occurring at a connection point of the switching transistor and the synchronous rectification transistor and a predetermined threshold voltage, compares the switching voltage with the predetermined threshold voltage, and at timing at which the ON signal is outputted from the output monitoring comparator, when the switching voltage is higher than the threshold voltage, nullifies the ON signal,
- wherein the pulse modulator comprises:
- a second flip-flop circuit set by the ON signal;
- and
- an ON time setting circuit which, after an ON time has passed from when the second flip-flip circuit was set, resets the second flip-flop circuit;
- and wherein an output signal of the second flip-flop circuit is outputted as the pulse signal.
A control circuit of a synchronous rectification type of step-down switching regulator, the control circuit comprising:
- an output monitoring comparator which compares output voltage of the switching regulator and a reference voltage that is a target value thereof and when the out voltage goes lower than the reference voltage, outputs an ON signal;
- a pulse modulator which generates a pulse signal which goes to a predetermined level in a predetermined ON time from when the ON signal was outputted from the output monitoring comparator;
- a driver circuit which generates a first and a second control signal based on the pulse signal outputted from the pulse modulator, and alternately turns ON a switching transistor by the first control signal and a synchronous rectification transistor by the second control signal;
- and
- a light load mode detector which receives a switching voltage occurring at a connection point of the switching transistor and the synchronous rectification transistor and a predetermined threshold voltage, compares the switching voltage with the predetermined threshold voltage, and at timing at which the ON signal is outputted from the output monitoring comparator, when the switching voltage is higher than the threshold voltage, nullifies the ON signal,
- wherein the driver circuit comprises:
- a third flip-flop circuit that is set by a signal, which is an inverse of the pulse signal, and reset by the ON signal, and generates the second control signal based on an output signal of the third flip-flop circuit.
Dependencies are inferred from the claim text.