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LM3410: Infrared lamp dimming current issue

Roy Chen52
Intellectual 395 points
Part Number: LM3410

Dear Sir,

We used the LM3410 to drive four infrared lamps. Our current limit is around 0.19/0.36=527mA (Vin range:3.3V~4.2V).

When PWM is adjusted, the measured current is below 40% duty cycle as follows:

Duty cycle 10% current 8mA
                 20% current 11mA
                 30% current 85mA
                 40% current 115mA
                 50% current 652mA
                 ......
               100% current 2A
The duty cycle is suddenly increased from 40% to 50% to more than 500 mA. In addition, during the test of the camera, we turned on the infrared in night vision mode, and there will be streaks on the screen. It was later discovered that it was caused by the PWM-controlled IC. Now it is necessary to change the PWM to a duty cycle of 100%. This phenomenon will disappear. However, when the duty ratio is 100%, the current will reach 2A, which is unacceptable. Please help us to see what method is available to reduce the current. Thank you!

The spec range of the infrared lamp is 1.8V and the current is 1A.

Schematic:

  • 0
    TI__Mastermind 28655 points

    Hello Roy,

    Can you get some oscilloscope pictures of Vin, Vout, the switch node and the output current?  If Rsns is 0.36 ohms it is not regulating correct.  100% duty cycle should be 0.53A.  Have you tried a higher voltage standard LED load.  IR leds Vf can become quite low at low current and higher temperature.

    Is this the 2 MHz version LM3410?  There is a minimum duty cycle for this part.

    Are the LEDs on a heatsink?  How hot are they getting?

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Intellectual 395 points

    Hi Sir,

    We found that the current meter is serially connected to the line current. If the PWM duty is adjusted to 50% or more, there will be a large current.

    There is no problem if the ammeter is not connected in series. I don't know if this will happen to this device.

  • 0 in reply to Roy Chen52
    TI__Mastermind 28655 points

    Hello,

    Make sure the current meter is no auto-ranging or use a resistor in series where you can measure the voltage across the resistor to get the output current.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points

    Hello,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue.
    If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Best Regards,