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The circuits we have discussed using the VIPer are suited for applications supplied directly off the mains. For applications that have a low voltage input, like battery powered systems, automotive lighting or applications like landscape lighting that operate from low voltages for safety reasons, a different configuration is required. For these applications, a low voltage solution with a buck configuration can easily implement the constant current drive. This schematic shows a typical device, the L5970 or 5973, that can be used as a constant current LED drive as well. The difference between the LED application and the standard voltage regulator application is that we are sensing the output current by sensing the voltage drop across the current sense resistor and actually regulating that voltage. You can see in the schematic that the feedback is taken from the current sense resistor in this circuit. The circuit is configured so the output current can easily be selected to be 350 mA, 700 mA or 1.05 A using jumpers.
