Variable on-time control method for high light-load efficiency, small output voltage ripple, and audible-noise-free operation
AssigneeSemtech Corporation
InventorsChin CHANG, Veter CHANG
Life of this patent
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Abstract
An apparatus and method of controlling power converters is achieved that produces high light-load efficiency and reduced output voltage ripple while maintaining quiet operation that is free from audible noise. The inventive method includes a variable on-time control circuit that is applicable to a wide variety of switching mode converters, including, but not limited to, boost converters, buck converters, buck-boost converters, single-ended primary inductor (SEPIC) converters, and other converter topologies, both isolated and non-isolated.
Claims13
For controlling a switching power converter having a primary switching element, an input voltage, an output voltage, and a load current, a variable on-time generator comprises:
- a primary feedback circuit comprising:
- a charge storage device connected in parallel with a bypass switch to a current source whereby the current source charges the charge storage device when the bypass switch is opened;
- and
- a comparison circuit connected to the charge storage device and to a reference voltage and having an output that changes state when the charge storage device reaches a voltage that is greater than the reference voltage;
- wherein the output of the comparison circuit is configured to control the primary switching element of the switching power converter;
- and
- at least one of a first variable control circuit and a second variable control circuit, wherein:
- the first variable control circuit comprises:
- a differential amplifier configured to compare the load current and the output voltage of the switching power converter;
- and
- a first transconductance amplifier connected to the current source of the primary feedback circuit and configured to shunt a portion of the current from the current source in response to an output of the differential amplifier of the first variable control circuit;
- and
- wherein the second variable control circuit comprises:
- a second transconductance amplifier connected to the current source of the primary feedback circuit and configured to shunt a portion of the current from the current source wherein the portion is dependent on the output voltage of the switching power converter.
A switching power converter receiving an input voltage and supplying a load current at an output voltage and comprising:
- a primary switching element;
- and
- a variable on-time control circuit operatively coupled to the primary switching element and comprising:
- a primary feedback circuit comprising:
- a charge storage device connected in parallel with a bypass switch to a current source whereby the current source charges the charge storage device when the bypass switch is opened;
- and
- a comparison circuit connected to the charge storage device and to a reference voltage and having an output that changes state when the charge storage device reaches a voltage that is greater than the reference voltage;
- wherein the output of the comparison circuit is configured to control the primary switching element of the switching power converter;
- and
- at least one of a first variable control circuit and a second variable control circuit, wherein:
- the first variable control circuit comprises:
- a differential amplifier configured to compare the load current and the output voltage of the switching power converter;
- and
- a first transconductance amplifier connected to the current source of the primary feedback circuit and configured to shunt a portion of the current from the current source in response to an output of the differential amplifier of the first variable control circuit;
- and
- wherein the second variable control circuit comprises:
- a second transconductance amplifier connected to the current source of the primary feedback circuit and configured to shunt a portion of the current from the current source wherein the portion is dependent on the output voltage of the switching power converter.
Dependencies are inferred from the claim text.