Method for starting up DC-DC converter
View Patent ↗Aspects of the invention provide a method for starting up a DC-DC converter by which an output voltage can be prevented from overshooting and body diodes of switching devices can be prevented from reverse recovery. In the start-up method, the phases of gate signals of third and fourth switching devices are gradually shifted relative to the phases of gate signals of first and second switching devices. With increase of the phase shift, a voltage on a primary side of a transformer is also increased, and an output voltage is also increased.
1. A method for starting up a DC-DC converter so as to obtain a DC output, the DC-DC converter including a full bridge formed by a first series circuit and a second series circuit connected in parallel to a DC power supply, the first series circuit including a first switching device and a second switching device connected in series, the second series circuit including a third switching device and a fourth switching device connected in series, an internal connection point of the first series circuit being connected to one end of a primary side of a transformer, an internal connection point of the second series circuit being connected to the other end of the primary side of the transformer, a rectification device being connected to a secondary side of the transformer, the starting-up method comprising the steps of:
turning on the first switching device with a first driving signal whose duty ratio is lower than 50%, turning on the second switching device with a second driving signal whose duty ratio is lower than 50% in a period when the first switching device is OFF, and driving the third switching device and the fourth switching device respectively with third and fourth driving signals whose duty ratios are lower than 50% and whose phases are shifted from the first and second driving signals, respectively, of the first switching device and the second switching device; and
gradually increasing the amount that the third and fourth driving signals are shifted from the first and second driving signals, respectively, to increase an output voltage value of the DC output gradually.
2. A starting-up method according to claim 1 , wherein when the output voltage value reaches a first value, the pulse widths of the first to fourth driving signals are increased to increase the output voltage value to a target value.
3. A starting-up method according to claim 1 , wherein when the output voltage value reaches a target value, the first and fourth driving signals are updated with new signals which will be ON in a period when the first and fourth switching devices should be ON concurrently, and the second and third driving signals are updated with new signals which will be ON in a period when the second and third switching devices should be ON concurrently.