| 主权项 |
1. An LED drive system which resides on a first integrated circuit (IC) and is arranged to control an off-chip power supply that supplies a common line voltage for two or more LED strings that are connected in series with respective current sink circuits at respective junctions, each of said current sink circuits arranged to cause a desired current to be conducted by the LED string to which it is connected, said LED drive system comprising:
a minimum circuit which receives the voltages at each of said junctions at respective inputs and which outputs a minimum voltage which is proportional to the least of the received voltages; and an I/O pin on said first IC which receives a signal that varies with the output of said minimum circuit, wherein said I/O pin is a feedback I/O pin; said LED drive system arranged such that, when said I/O pin is coupled to the control input of an external power supply which produces an output voltage that varies with a signal applied to said control input, said LED drive system controls said power supply's output voltage, the output voltage of said external power supply providing said common line voltage; and said LED drive system further arranged such that, when said external power supply which produces an output voltage that varies with a signal applied to a control input is a DC-DC converter having a transformer with a primary side and a secondary side, with said secondary side coupled to an output node, and an optocoupler having an input which is coupled to said feedback I/O pin and with the voltage at said output node being said common line voltage, said LED drive system varies the signal at said feedback I/O pin as needed to produce a common line voltage which makes said minimum voltage equal to said desired junction voltage. |
