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WEBENCH® Tools/LM3409: How to get the efficiency > 98%?

anandam boora
Prodigy 120 points
Part Number: LM3409

Tool/software: WEBENCH® Design Tools

We are using the LM3409MY/NOPB Driver ic for our LED street lights. But we are getting only 89% efficiency. we used the webench for driver design. And the input range is 10.5 to 17V and the output is 9.67V @1.6A. Can you suggest how to improve the efficiency on this driver pls?

With regards

anandam boora,

Intelizon Energy Pvt Ltd.,

Hyderabad, India

Contact No. +91-9346116230

  • 0
    TI__Mastermind 28655 points
    Hello Anandam,

    Improving efficiency or optimizing efficiency requires going through all the design calculation for your application. The method I would use is to create a spreadsheet of all the components that dissipate power, the freewheel diode, the switching MOSFET conduction loss, the current sense resistor, the gate drive and switching loss of the switching MOSFET and any other power loss components.

    Example, if you are using the highest current sense voltage it will be 246 mV. At 10.5V input the duty cycle will be near maximum, if the inductor current ripple is low the average voltage will be near 246 mV on the current sense resistor. If the duty cycle is 90% the power dissipation in the current sense resistor will be 246 mV * 0.9 * 1.6A = 354 mW. output power is 9.67V * 1.6A = 15.47W. The efficiency taking into account only the current sense resistor loss would be 15.47W/(15.47W+0.354W) = 97.8%. Just the current sense resistor is responsible for a 2% loss in this case. Add in the MOSFET switching loss, conduction loss, diode freewheel loss, inductor loss and other losses you will be able to see where the losses are and try part changes to improve or operating condition.

    An improved for the current sense resistor loss would be to lower Viadj however the accuracy will become worse so there are tradeoffs.

    Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points

    The same components what suggested by WEBENCH design tool is used in our driver circuit. So what is your suggestion / adivse on More efficeincy >95% pls

    Regards

    anandam boora

  • 0 in reply to anandam boora
    TI__Mastermind 28655 points
    Hello Anandam,

    Webench for LED drivers gives you a start for the design of an LED driver. If you are looking to make the efficiency higher I would create a design spreadsheet that shows all of the losses in the components. This way you can change operating parameters and parts to see what increases efficiency. In my example above the current sense resistor is approximately 2% efficiency loss. If Viadj was set to half and the current sense resistor set to half this loss would be also cut in half. The only way to optimize is to know what everything is dissipating. the datasheet has a lot of the design equations. The key ones to calculate are MOSFET conduction loss, MOSFET switching loss, Freewheel diode conduction loss, inductor losses, both conduction and switching, then bias losses (the power required for the IC, gate drive and other circuitry). This is a start, there are other losses as well.

    Regards,