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Doubt regarding performance of DC-DC converter when supply current is low

Niral Kalavadia
Expert 1130 points

Hello everyone,

I am an embedded software engineer so not having depth knowledge of power electronics. I have designed DC-DC converter using Webench with following parameters.

  • Vin Min : 6v, Vin Max : 48v
  • Vout : 5v
  • Iout : 5Amp

I have developed PCB and it is working like a charm (A big thanks to TI Webench :) :) ) however I am a bit confuse about input supply i.e if I give input supply of 12v/350ma DC to this circuitry will it be capable of driving load of 5Amp? As I mentioned earlier I am an embedded software engineer I am not able to understand this phenomenon. It would be great if someone can help me to understand this.

Thank you,

nIk

  • 0
    TI__Expert 3085 points

    Niral,

    Thanks for your question. I am glad know that WEBENCH tools helped you design your board. 

    The input supply has to be have enough current supplying capability to be able to supply the output current. As you know, efficiency is output power divided by input power. Electrical power is product of voltage and current. Expressed in equation form

    Efficiency = Pout / Pin

    Where

    Pout = Vout * Iout

    Pin = Vin * Iin

    Hence, we can solve for input current

    Iin = ( Vout*Iout / Efficiency )/Vin

    Putting the numbers for your design in and assuming a theoretical maximum efficiency of 100%, the input current has to be at least

    Iin = (5 * 5 / 1.0 )/12 = 2.1 A

    This means that the input supply must be able to supply at least 2.1 A at 12 V input. Your input source, you mentioned, can supply on 0.35 A, which is less than this. So either you will have to live with lower output current our find a supply with more supply capability.

    Regards.

  • 0 in reply to Surinder Singh
    Expert 1130 points

    Surender,

    Thank you for clear information.

    Regards,

    Niral