Hi
We have been using an LM3519 LED driver as per the datasheet to drive LEDs that require 20mA.
We have made over 20 boards and have identified only 2 boards that work well and provide ~7V across the LED (1 LED in circuit), 12.7V at 2LEDs in series and 18V for 3 LEDs. All the other boards give 5, 10 and 16V respectively and we do not get as much light out of the same LEDs on these boards.
The circuit is very compact and we cannot see any dramatic changes in values between good and bad boards.
Can anyone answer the following questions
1. What might contribute to these changes and how can we ensure that we get the higher voltages (and better light output).
2. Is there a better option for driving Constant current 20-25mA into an LED that has Vf of 5.8-7V?
many Thanks in advance
DEvans