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LM2678 Current Problem

Juvenalis Kantawiria
Prodigy 20 points

Hi there,


My name is kara and I really need help to solve my problem. I am building my DCDC buck  converter using LM2678-ADJ. I am hoping to get 12V output at the end. I have finished wired up my circuit in bread board and tested it. I managed to get 12V (no load). I have also tested it using 10K ohm and measure the voltage across. But it seems that there is no current flowing. And if I put my motor as the load, it doesnt work at all. There is tiny rotation in the beginning and then nothing. Hope anyone can help me with this problem. THank you so much, and have a good day.

Kara

  • 0
    TI__Genius 15810 points
    Hello,
    Please refer to this thread that we recently answered that has a similar issue mentioned: e2e.ti.com/.../452256

    In a nutshell, bread-boarding a DCDC regulator will cause problems in the application. High frequency switching and long wire lengths cause voltage spiking. Long wire lengths will also add more impedance and limit the current delivered.

    Regards,
    Akshay
  • 0 in reply to Akshay Mehta
    Prodigy 20 points

    My components are not that much different from the example you gave. I tried to avoid long wire but it seems the problem is not that since the motor is not running at all. Also, if I change my input, the output will change as well. Does that means something wrong the IC when I solder it?

    Other question, do you have a circuit diagram for lm2678-s adj application for 12V output fixed? Thank you so much.

  • 0 in reply to Juvenalis Kantawiria
    TI__Genius 15810 points

    I do not have your exact input requirements. So I created a schematic for 24Vin to 12Vout at 5A. Here is the attached schematic with BOM components. LM2678ADJ_12V.pdf

    You could send us your schematic and we can review it as well. But the biggest issue is the wired connection. You could even make a one layer board and that would still work better than the wired connection. There can be anything that could go wrong with the connection.


    Regards,

    Akshay