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LM3488: Efficiency matter

Piotr Rozycki
Prodigy 160 points
Part Number: LM3488

Hello,

I have measured efficiency of the whole driver I built (with R17=0R). The max efficiency is 82%. Comparing to WEBENCH results it is about 10% lower. Provided the input voltage is higher comparing to WEBENCH design (where Vin max = 40V), is there any chance to obtain better efficiency?

Tab 1

Vin (DC) [V] Iin (DC) [A] Pin [W] Vout (DC) [V] Iout (DC) [A] Pout [W] Efficiency [%]
53.74 0.27 14.51 17.64 0.68 12.00 82.67
56.57 0.26 14.71 17.64 0.68 12.00 81.56
63.64 0.23 14.64 17.64 0.68 12.00 81.95
70.71 0.21 14.85 17.64 0.68 12.00 80.78
77.78 0.19 14.78 17.64 0.68 12.00 81.17
84.00 0.18 15.12 17.64 0.68 12.00 79.33

Fig 1

Fig 2 WEBENCH diagram

Fig 3 WEBENCH efficiency chart

Thanks.

Kind Regards,

Piotr

  • 0
    TI__Guru* 78310 points
    How did you measure the efficiency? Have you included the power taken by the dimming control circuit as well as other additional circuits that are extra to the Webench model?
  • 0 in reply to Youhao Xi
    Prodigy 160 points

    Yes, you are right. I should have isolated the converter first then measure the efficiency.

    However, the currents of different parts of the whole circuit are as follows:

    - dimming control <4mA

    - 5V reg. 6mA

    - LM3488 3mA

    So, the power loss in those components should be: P = 17.6V x (4+6+3)mA = 0.23W,

    where 17.6V is the output voltage of the converter.

    I doubt that 0.23W taken by those components changes the efficiency significantly.