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TLC5940 control reserve

r.staffen
Prodigy 70 points
Other Parts Discussed in Thread: TLC5940

how much should the V_led exceed the forward voltage of the led?

Does the TLC need some control reserve?

I tried to figure it out with the datasheet but i could not found it.

with best regards,

René

  • 0
    TI__Intellectual 955 points

     Hello Rene,

     Figure 5, OUTPUT CURRENT vs OUTPUT VOLTAGE graph shows how much output voltage TLC5940 needs.

    If you want to set the output current to 60mA, then I would recommend you to set output voltage 0.8~1.0V.

    The output voltage is determined by LED forward voltage and LED power supply voltage like the following equation.

    VOUT = VLED - (Vf * N)

    Where:  VLED = LED lamp power supply voltage, Vf = LED lamp forward voltage at the current, N = the number of LED lamp connected in series.

    So if you use 2 LED in serise at 60mA and LED maximum forward voltage is 3.5V, then the LED power supply voltage should be set to the following

    VLED.

     VLED = VOUT + (Vf * N) = 1V + (3.5V * 2) = 8.0V.

     Best regards,

     Kazuya.Nakai

     

     

     

     

     

     

     

  • 0 in reply to Kazuya Nakai
    Prodigy 70 points

    ah, ok Thank you very much.

    One more thing:

    Fig 5 and Fig 6. show the behaviour for VCC=5V..

    Any idea how much they differ if VCC is 3.3V?

    Best regards,

    René

  • 0 in reply to r.staffen
    TI__Intellectual 955 points

     Hello Rene.

     3.3V curve are almost same as 5V. But the maximum output current in 3.3V is 60mA.

     Best regards,

     Kazuya Nakai.