• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 119 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Original question:

LM3409-Q1: PWM dimming issue

LM3409-Q1: can't work when input voltage is 12V

Sherry Liang
Genius 10255 points
Part Number: LM3409-Q1

Dear team,

When the input voltage is 12V, our device can't start up. When the input voltage is 8V or 8.5V, our device CAN start up. In addition, if removing capacitor C5, our device CAN start up even though input voltage is 12V. The PWM frequency is 30Hz. Could you please help analyze this phenomenon?

Thanks & Best Regards,

Sherry

  • 0
    TI__Mastermind 28655 points

    Hello Sherry,

    I calculated the design based on the schematic values.  What is MOSFET Q1 (part number)?  I don't recommend powering up this circuit with C5 removed, it can cause catastrophic failure.  What is the forward voltage of the LEDs at 2A (I used 6V for the calculations below)?  What is the part number or datasheet for L2?  The last equations are for calculating if the output voltage can get above Voff, it is fine.  Can you get an oscilloscope picture of the SW node when it is not starting?

    Vin 12 V
    Vled 6 V
    Roff 15000 ohm
    Coff 4.9E-10 F
    Rcs 0.1 ohm
    Lind 0.00001 H
    Riadj 249000 ohm
    Iiadj 0.000005 A
    Viadj 1.245 V
    Vcs 0.249 V
    Ipeak 2.49 A
    Voff 1.243 V
    Ioff 0.000358567 A
    toff 1.69862E-06 sec
    duty 0.5  
    ton 1.69862E-06 sec
    Fsw 294355.8759 Hz
    diLoff 1.019174491 Apkpk
    Iave 1.980412754 Aave
    Eind 3.10005E-05 J
    Cout 0.0000001 F
    Vout 24.9 V

    Best Regards,