Isolated direct-current (DC) to DC switching voltage converters use transformers to convert power from an input source into power for an output load. Such a voltage converter includes primary-side power switches that convert DC input power into alternating-current (AC) power that is fed to the primary side of a transformer. AC power supplied on the secondary side of the transformer is rectified to convert it back into DC power which, in turn, is provided to the output load.
In order to prevent damage to the primary-side power switches or the transformer itself, care must be taken to ensure that the core of the transformer does not magnetically saturate. This is typically accomplished by oversizing the transformer and/or using the current in the primary-side power switches to detect transformer core saturation. Should transformer core saturation be detected thusly, power transfer through the transformer is curtailed. More advanced techniques may track the transformer core flux, e.g., using a volt-second measure based upon a voltage of the transformer. A controller of the voltage converter may use the tracked transformer core flux to keep the flux well-balanced between positive and negative excursions, and to curtail power transfer if the tracked flux is approaching a level corresponding to a core saturation limit of the transformer.
A load transient, e.g., a step increase in the power required by the load, is preferably handled by increasing a current output from the voltage converter at a high rate until the voltage provided to the output load approaches a desired output level. The output current must be increased such that it does not cause saturation of the transformer core. Furthermore, the voltage converter components including, in particular, an output inductor must be sized such that a maximum output current is accommodated.
Techniques are desired for providing fast transient response within a voltage converter while avoiding transformer core saturation and without increasing the size of the transformer or an output inductor of the voltage converter.