Light load current-mode control for switched step up-step down regulators
AssigneeLinear Technology Corporation
InventorsXunwei Zhou, Randy G. Flatness
Life of this patent
Estimating the term…
Abstract
A switched regulator circuit provides step-up and step-down operation at high efficiency during light load conditions. Switching loss is reduced in a four switch arrangement by limiting bottom MOSFET switching frequency. The possibility of overcharge in boost mode operation has been avoided by automatically changing to a buck mode operation in response to sensed parameters.
Claims10
In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the first inductor terminal and a common connection, a third switch connected between the second inductor terminal and the common connection, a fourth switch connected between the second inductor terminal and an output terminal, and a sensing element for sensing inductor current, the sensing element connected between the common connection and a node joining the second switch and the third switch, a method for regulating the voltage at the output terminal at a level less than the voltage at the input terminal, the method comprising the steps of:
- setting the second and third switches to an off state and the fourth switch to an on state;
- generating a clock signal,
- at each clock, setting the first switch to an off state and maintaining the second switch off for a fixed time period;
- sensing inductor current during the fixed time period;
- in response to the sensed inductor current exceeding a first predetermined threshold level, turning on the second switch after the fixed time period;
- turning off the second switch when current falls below a second predetermined threshold level;
- and
- maintaining the first switch off until occurrence of an output voltage condition.
In a circuit comprising an inductor having first and second terminals, a first switch connected between the first inductor terminal and an input terminal, a second switch connected between the first inductor terminal and a common connection, a third switch connected between the second inductor terminal and the common connection, a fourth switch connected between the second inductor terminal and an output terminal, and a sensing element for sensing inductor current, the sensing element connected between the common connection and a node joining the second switch and the third switch, a method for regulating the voltage at the output terminal at a level greater than the voltage at the input terminal, the method comprising the steps of:
- generating a repetitive clock signal;
- setting the first switch to an on state and the second and fourth switches to an off state;
- in response to each clock signal, turning the third switch on;
- sensing inductor current;
- in response to the sensed current rising to a boost mode threshold level, turning the third switch off;
- in response to an output voltage condition, after the third switch turns off, turning on the second and fourth switches and turning off the first switch.
A regulator comprising:
- an inductor having first and second terminals;
- a first switch connected between the first inductor terminal and an input terminal;
- a second switch connected between the first inductor terminal and a common connection;
- a third switch connected between the second inductor terminal and the common connection;
- a fourth switch connected between the second inductor terminal and an output terminals,
- a sensing element for sensing inductor current, the sensing element connected between the common connection and a node joining the second switch and the third switch, and
- a control circuit configured to:
- set the second and third switches to an off state and the fourth switch to an on state prior to receipt of a clock signal pulse;
- upon receipt of the clock signal pulse, set the first switch to an off state and the second switch off for a fixed time period;
- in response to the sensed inductor current exceeding a first predetermined threshold level during the fixed time period, turn on the second switch after the fixed time period;
- turn off the second switch when current falls below a second predetermined threshold level;
- and
- maintain the first switch off until an output voltage condition occurs.
A regulator comprising:
- an inductor having first and second terminals;
- a first switch connected between the first inductor terminal and an input terminal;
- a second switch connected between the first inductor terminal and a common connection;
- a third switch connected between the second inductor terminal and the common connection;
- a fourth switch connected between the second inductor terminal and an output terminal,
- a sensing element for sensing inductor current, the sensing element connected between the common connection and a node joining the second switch, and the third switch, and
- a control circuit configured to:
- set the first switch to an on state and the second and fourth switches to an off state;
- in response to receipt of a clock signal pulse, turn the third switch on;
- in response to inductor current rising to a boost mode threshold level, turn the third switch off, and
- in response thereafter to an output voltage condition, turn on the second and fourth switches and turn off the first switch.
Dependencies are inferred from the claim text.