Power converter with adaptive active clamp
AssigneeDialog Semiconductor GmbH
InventorXiaoyong Zhang
Life of this patent
Estimating the term…
Abstract
An active-clamp flyback converter is provided with improved active-clamp switch control that switches on an active-clamp switch at an active-clamp switch on-time that equals a power switch on-time minus a peak charge time for an active-clamp capacitor. The peak charge time is the duration between the switching off of the power switch transistor and when the charging current through the active-clamp capacitor falls to zero. The controller measures this peak charge time following the switching off of the power switch transistor and then applies it to the subsequent switching on of the active-clamp switch so that the active-clamp switch is switched on at the power switch on-time minus the peak charge time.
Claims19
An active-clamp flyback converter, comprising:
- a power switch;
- an active-clamp switch;
- an active-clamp capacitor in series with the active-clamp switch;
- and
- an active-clamp controller configured to measure a peak charge time of the active-clamp capacitor and to switch on the active-clamp switch at a time equaling a difference between a turn-on time for the power switch and the peak charge time.
A method of operation for an active-clamp flyback converter, comprising:
- measuring a peak charge time period during which an active-clamp capacitor charges to a peak charge in response to a switching off of a power switch transistor;
- during an off-time of the power switch transistor after the active-clamp capacitor is charged to the peak charge, switching on an active-clamp switch transistor at an active-clamp on-time that equals a difference between a subsequent power switch on-time of the power switch transistor and the peak charge time period;
- switching off the active-clamp switch transistor at an active-clamp off-time that equals the active-clamp on-time plus the peak charge time period;
- and
- switching on the power switch transistor at the subsequent power switch on-time.
An active-clamp controller for an active-clamp flyback converter, comprising:
- a comparator configured to compare a voltage across an active-clamp resistor to a threshold voltage;
- a counter configured to provide a count representing a peak charge time of an active-clamp capacitor, the counter being further configured to stop a counting of the count in response to an output signal from the comparator indicating that the voltage across the active-clamp resistor equals the threshold voltage;
- and
- an active-clamp switch transistor gate driver configured to switch on an active-clamp switch transistor at an active-clamp on-time that equals an on-time of a power switch transistor minus the peak charge time.
Dependencies are inferred from the claim text.