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LM3414HVMREVAL: Issue on PWM dimming frequency

Claudio Pacini1
Prodigy 20 points
Part Number: LM3414HVMREVAL
Other Parts Discussed in Thread: LM3414HV, LM3414

Hello everyone, I bought the LM3414HVREVAL board to test the LM3414HV chip because I want to use it for a project of LED driver. I found some issue with the PWM dimming frequency that confused me, please can you help me?

The issue is: 

- With a PWM frequency from 200Hz to 400Hz at 70to80% of duty cycle the LED flicker a lot and this is unacceptable;

- With a PWM frequency higher that 1kHz instead the LED works great and no problem found when dimmered.

So I don't know how this can happen, on the datasheet of the component LM2414HV there is: 

" To ensure normal operation of the LM3414/HV, TI recommends setting the dimming frequency not higher than 1/10 of the switching frequency..."

And this is exactly what I've done. Could you please help me with this issue?

I want a PWM frequency from 200Hz to 400Hz because most of commercial dimmer work at this output frequency.

  • 0
    TI__Mastermind 22745 points

    Hi Pacini1,

         Could you share some test waveform about the Inductor current, Vout and output current? And how about your supply voltage and LED configuration?

    BR

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 20 points

    Hello Mr. Sean,

    unfortunately I can't share with you this information. I don't have any instrumentation to test that, I have only a multimeter with me. The circuit is exactly the same as the LM341HVMREVAL evaluation board.

    There is a way to solve the problem without the information you asked for? 

    Thank you, 

    Claudio Pacini.

  • 0 in reply to Claudio Pacini1
    TI__Mastermind 22745 points

    Hi Pacini,

        I'm sorry that give out more analysis since there are no test waveforms. Maybe you need to check your configuration and PWM signal again.

    BR

    Sean