Method and apparatus providing a multi-function terminal for a power supply controller

#1. Field of the Invention

#The present invention relates generally to power supplies and, more specifically, the present invention relates to a switched mode power supply controller.

#2. Background Information

#The present invention detailed illustrated by way of example and not limitation in the accompanying figures.

#FIG. 1 is a schematic illustrating one embodiment of a power supply including a power supply controller having a multi-function terminal in accordance with the teachings of the present invention.

#FIG. 2A is a schematic illustrating one embodiment of a power supply controller having a multi-function terminal configured to limit the current of the power switch in the power supply controller to a desired value in accordance with the teachings of the present invention.

#A method and an apparatus providing a multi-function terminal in a power supply controller is disclosed. In the following description, numerous specifically details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail In order to avoid obscuring the present invention.

#In one embodiment of the present invention, a power supply controller is provided with the functionality of being able to remotely turn on and off the power supply. In another embodiment, the power supply controller is provided with the functionality of being able to externally set the current limit of a power switch in the power supply controller, which makes it easier to prevent saturation of the transformer reducing transformer size and cost. Externally settable current limit also allows the maximum power output to be kept constant over a wide input range reducing the cost of components that would otherwise have to handle the excessive power at high input voltages. In yet another embodiment, the power supply controller is provided with the functionality of being able to detect an under-voltage condition in the input line voltage of the power supply so that the power supply can be shutdown gracefully without any glitches on the output. In still another embodiment, the power supply controller is provided with the functionality of being able to detect an over-voltage condition in the input line voltage of the power supply so that the power supply can be shut down under this abnormal condition. This allows the power supply to handle much higher surge voltages due to the absence of reflected voltage and switching transients on the power switch in the power supply controller. In another embodiment, the power supply controller is provided with the functionality of being able to limit the maximum duty cycle of a switching waveform generated by a power supply controller to control the DC output of the power supply. In so doing, saturation of the transformer during power up is reduced and the excess power capability at high input voltages is safely limited. Increased duty cycle at low DC input voltages also allows for smaller input filter capacitance. Thus, this feature results in cost savings on many components in the power supply including the transformer. In yet another embodiment, some or all of the above functions are provided with a single multi-function terminal in the power supply controller. That is, in one embodiment, a plurality of additional functions are provided to power supply controller without the consequence of adding a corresponding plurality of additional terminals or pins to the integrated circuit package of the power supply controller. In one embodiment, one or some of the above functions are available when positive current flows into the multi-function terminal. In another embodiment, one or some of the above functions are available when negative current flows out from the multi-function terminal. In one embodiment, the voltage at the multi-function terminal is fixed at a particular value depending on whether positive current flows into the multi-function terminal or whether negative current flows out from the multi-function terminal.

#The multi-function features listed above not only save cost of many components and improve power supply performance but also, they save many components that would otherwise be required if these features were implemented externally.