• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 512 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3414HV: LM3414HV Current LED Driver

Robet Le
Prodigy 20 points
Part Number: LM3414HV
Other Parts Discussed in Thread: LM3414,

LM3414HV is Current LED Driver and range from 350 ma to 1A for output current. If I add a resistor which is serial with LED, output current through LED will be changed, it will drop down below the value of current set by resistor RADJ. Can I select the value of serial resistor to set current through the LED down to 40 ma? Is this configuration valid for LM3414 device? Does it affect the LM3414 device (unstable) for long term?

  • 0
    TI__Mastermind 28655 points

    Hello Robet,

    Adding a series resistor doesn't change the current regulation.  It is a current regulator, it supplies current.  I wouldn't recommend using the LM3414 at 40 mA.

    What are you trying to do?  Perhaps there is a different part that will work.  The TPS92515A can regulate down to 40 mA.

    What is your input voltage and range, LED voltage and any other operating you plan on using?

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    The input voltage is range from 18v to 32v.

    We already have circuit board with LM3414 that works for our 600 ma Laser Led. Now, the new coming Laser Led is 40 ma and we want to find the way to work with our current circuit board.

    That is a reason we ask you a question is there other way to work around this LM3414 device for new 40 mA Laser Led?

    Here are some options:

    Option#1:

    Set output current of LM3414 to 350 ma (minimum) and duty cycle to 11%. So the Iavg will be 38.5 ma.

    Option#2:

                    Adding a series resistor. Like you said this option does not change the current regulation.

    But the LM3414 simulation(TINA) allows me to set current by adding series resistor.

    Option #3:

                    Adding a parallel resistor to take 310 ma on this branch and leave 40 ma for Led branch.

    Option #4: Any suggestion from you

    Let me know your thought or the alternative device is the only choice.

  • 0 in reply to Robet Le
    TI__Mastermind 28655 points

    Hello Robet,

    option 1:  You can set the current to 350 mA and use PWM dim at 11%, this will work

    option 2:  If you add a series resistor in the LED string it will not change the current regulation set point.  I would guess the LM3414 is just turning on and the current is being limited by the resistor.  Try changing the input voltage and see if the current changes.

    option 3:  This may or maynot work but it will be a large efficiency drop.  If set point accuracy is +/- 5% at 1A, this is +/- 50 mA (see option 4).

    option 4:  You can use the analog dimming circuit in the datasheet, it shows dimming down to 100 mA per section 7.3.5 per the datasheet and add additional 60 mA of load.  Since the current sense is internal the accuracy may not be very good at this level.  According to how this is done in that section you could probably set the current to 100 mA via the resistor.  Again, adding 60 mA load may make the 40 mA regulation very poor.  Example, if 100 mA is +/-50% accurate (note:  I do not know what the accuracy will be at 100 mA, basing this on worst case 0.95A to 1.05A set point accuracy at 1A over operating temperature range), the 40 mA would be +/- 125% accurate.  This means completely off to 90 mA.

    Of these options I would use option 1, it will be the most accurate and probably the only one that will work.  If the laser LED cannot handle the peak current you will need to have a capacitor across the laser LED

    Best Regards,