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TPS61500: Fliker LED with Vin = 3V and Vout = 11.3V Iout = 400mA

Part Number: TPS61500

Hi,

I am using the TPS61500 led driver for a lighting application. I have to drive 20 LEDs with an output voltage of 11.3V and a current of 400mA. I used an 8,2uH 3A inductor with a frequency of 600kHz. If I power the driver with 4V, I have an efficiency of 84% and the temperatures of the inductor and the driver are around 55 ° C. If I go down to 3V in input, the efficiency drops to 69% and the temperatures of the inductor and the driver rise above 90 ° C. When temperatures rise above 90 ° C, I start to see the fliker and the TPS61500 limits the output current, the thermal protection certainly intervenes.

What do you recommend to increase the efficiency on the 3V input?

I would like to know if there is a spreadsheet of the TPS61500.

To follow the schematic:

Test Report Table:

Best Regards

Davide Facchini

  • Hi Davide,

    It would be helpful to increase switching frequency. BTW, could you remove the output resister (3R3)? This will decrease the voltage difference between Vin and Vout and increase system efficiency.

    There is no spreadsheet.

    BR,

    Robin

  • HI,

    The five 3.3ohm resistors are used to compensate for any voltage differences in each branch due to the variation of the Vf of the LEDs. However each branch has about 80mA and each resistor dissipates 20mW, for a total of 100mW on 4.2W of output, I would gain 2.38% on the efficiency.

    I follow your suggestion and try to work more frequently.

    BR


    Davide

  • Hi,

    I am writing to communicate that I have solved the problem. I have recalculated all the parameters and for a frequency of 600kHz the optimal inductance value is 22uH 3A. So by varying only the inductor L3 I obtained the following results:

    As you can see from the data, I purposely checked the worst case with a Vin equal to 2.8V. With a 22uH inductor I gained about 10% efficiency.

    Davide