Led Constant Current Source Scheme

The LM317L wants to see 1.25 V between its VOUT pin and the Vadj pin, and it will do whatever it CAN to keep that voltage differential between them. So if a resistor is put in series with the output, and the Vadj pin is connected to the load side of the sense resistor, a current source is set up which follows Equation 1: But what if a series/parallel combination of LEDs is wanted, The following circuit works fine, assuming that there are not large variations in the forward voltage drop of the LEDs There could be a problem however if one of the strings opens up for some reason. The LEDs that remain would have 50% more current flowing through them, which could cause them to be driven too hard and fail. So how does one get around this problem,
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Led Constant Current Source Scheme application circuits
Led Constant Current Source Scheme application circuits



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