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LM3519 for driving LEDs - variation in output voltage

david evans
Prodigy 10 points
Other Parts Discussed in Thread: LM3519, TPS61161, TPS61158

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

  • 0
    TI__Intellectual 1040 points

    Hello,  what value of inductor are you using for the application (value and part number)?  The switching frequency of this part is dependent on the inductance, input voltage, load current, and output voltage.  Because of this , you could be running into peak current limitations which could be limiting your output power.  A better device is something that switches at a constant frequency such as the TPS61158 or the TPS61161.

    Thanks

    Travis