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SkyDvv , 05-02-2024, 09:45 AM

I designed a 42V -> 12V buck converter that can drive up to 20 current.
when I got the PCB and assembled it, the inductor keeps heating up at no load and I don't know why.
I looked for it and people said check for core loss but i can't find it anywhere in the datasheet
https://www.lcsc.com/datasheet/lcsc_datasheet_2304140030_Chilisin-Elec-MHCC12050-1R0M-R7_C329553.pdf
I used MHCC12050-1R0M-R7
it's maximum ripple current said to be 40%, i designed it to be 44% but i don't think that is the problem, the heat builds up like creazy, I can't even debig it with OSC as I keep disconnecting it before it burns.

SkyDvv , 05-02-2024, 09:56 AM

NVM, I just found out maximum voltage is 30V

SkyDvv , 05-02-2024, 10:12 AM

Can this problem be solved as it's a graduation project and there's no enough time to buy and ship a new ones or even edit the design.

QDrives , 05-02-2024, 09:36 PM

I do not think the core losses would be a problem at no load. But the question is: is it no load? Is there a short somewhere that causes the inductor to heat up.
If you remove the connector and use a lab power supply to supply the 12V, what currents are drawn?

SkyDvv , 05-02-2024, 09:41 PM

I thought of that and measured the resistance between 12 and gnd terminals and it was pretty hight so I guess no.
Unfortunately I'm not using or having bench power supply, I use 10s4p battery pack.

QDrives , 05-02-2024, 09:53 PM

1) A multimeter does not output 12V for the resistance measurement.
2) If I run the webench power designer it comes with 4.7uH and 3x 22uF. I see three 1206 ceramic caps as the schematic mentions 22uF. The DC bias losses of those size+capacitance capacitors will be terrible. You may want to test with at least 9 of those. And make sure that they are at least 16V or more! Or add an electrolytic capacitor.
3) Clean the board. I have seen flux residues cause problems.

SkyDvv , 05-03-2024, 12:23 PM

No I meant I measured while power was off, I sure that there's no shorts.

About the caps yeah it was a mistake I have must been used an electrolytic caps at the output.

I tried to fix it by adding higher inductance coil and it didn't heat that much.
So my guess is 44% was really high :" (about 9A ripple) that is really high
I put 2uH which decreaeed the ripples to 22% and it make things better.
I guess cheap selections of components aren't going to work all the time. I need to increase the inductance, capacitors, recalculate my equations and go for another version.

SkyDvv , 05-03-2024, 12:25 PM

What I can do now is adding electrolytic caps on those 12V-GND trminals and solder the higher inductor I had from the past (it's current limit is 10A) and decrease current consumption of the drivers.

QDrives , 05-03-2024, 04:00 PM

If you run a very simple simulation like I made here, you see that the current ripple is ~100A! Yes, that will heat up your inductor fast.

SkyDvv , 05-04-2024, 04:02 PM

I'll run my calculations again

QDrives , 05-06-2024, 12:45 AM

Also check with Webench: https://webench.ti.com/power-designer/switching-regulator/customize/26?VinMin=38&VinMax=50&O1V=12&O1I=20&base_pn=LM5145&AppType=None&Flavor=None&op_TA=30&origin=pf_panel&lang_chosen=en-US&optfactor=3&Topology=Buck&flavor=None&VoltageOption=None