Soft-start for resonant converters
An LLC converter includes a switching stage including primary transistors, a resonant stage connected to the switching stage, a transformer including a primary winding connected to the resonant stage and a secondary winding coupled with the primary winding, a rectifying stage connected to the secondary winding of the transformer and providing an output voltage of the LLC converter, and a controller configured and/or programmed to, during start-up, control the output voltage by switching the primary transistors based on a first reference voltage that exponentially increases during start-up and a second reference voltage that is based on a resonant current of the resonant stage.
1. An LLC converter comprising:
a switching stage including primary transistors;
a resonant stage connected to the switching stage;
a transformer including:
a primary winding connected to the resonant stage; and
a secondary winding coupled with the primary winding;
a rectifying stage connected to the secondary winding of the transformer and providing an output voltage of the LLC converter; and
a controller to control the output voltage during start-up by switching the primary transistors based on a first reference voltage that exponentially increases during start-up and a second reference voltage that is based on a resonant current of the resonant stage.
2. The LLC converter of claim 1 , wherein the primary transistors are switched with zero-voltage switching.
3. The LLC converter of claim 1 , wherein the controller adds the first reference voltage and the second reference voltage.
4. The LLC converter of claim 1 , wherein the second reference voltage is zero unless an average resonant current is below a threshold current.
5. The LLC converter of claim 1 , wherein the second reference voltage is limited to be between zero and a third of a maximum reference voltage.
6. The LLC converter of claim 1 , wherein the primary switches are arranged in either a half-bridge or a full-bridge configuration.
7. The LLC converter of claim 6 , wherein the resonant stage includes a split resonant capacitor.
8. The LLC converter of claim 1 , wherein the resonant stage includes a resonant capacitor and a resonant inductor.
9. The LLC converter of claim 1 , wherein the rectifying stage includes synchronous rectifiers connected to the secondary winding.