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Comments on Humming noise from a boost converter's inductor

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Humming noise from a boost converter's inductor

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My step-up converter makes audible noise both with and without a load.I am almost certain it is the inductor, because when I hold my finger on it I can feel vibration and it gets quieter. Unfortunately, I do not own an oscilloscope and cannot inspect what is going wrong. Here is the schematic: Image alt text

All the capacitors are ceramic, inductor is FXL0530-100-M, and the converter datasheet can be found here . On page 14, FIGURE 6-8 the recommended values are shown. Only thing I have changed are resistor values to match my output voltage, but this is a minor change. I read about audible issues with converters, and one of the points mentioned was that picking an IC with a higher switching frequency can help, but this particular one is at 1MHz, well above the one mentioned in the article I read.

What could be the reasons for this humming noise, and how could they be mitigated?

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General comments (2 comments)
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A couple of problems stick out; one glaring and one a little subtler. Read this in the data sheet: -

Image alt text

You have the enable pin connected to your 25 volt output. I'm not saying this is definitely causing your problems but you might well have broken the chip in some way that gives you the symptoms you are seeing: -

Image alt text

Other than that your circuit values looks compatible with the data sheet but what is the output load you are using?

The inductor you have used isn't the Murata LQH43CN100K03 part recommended in the data sheet of the chip - is there a reason why you have chosen that part? I'm not convinced that the inductor you have chosen is suitable for such high frequency operation. In the data sheet they don't give much detail about self-resonant-frequency whereas the Murata part is quoted at 23 MHz.

The inductor you have chosen only says that the inductance was tested at 100 kHz and this, in my opinion, hints that it probably isn't suitable for a boost converter running at nominally 1.2 MHz.

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General comments (1 comment)
General comments
Kranulis‭ wrote over 4 years ago

The EN_25V is just a name for me to remember what it does, it actually has only 5V on there. But I see that it can be confusing. I am loading numitron tube segments, which each takes 0.5mA at 25V. Regarding the inductor, I chose another one because the recommended one was out of stock. I will try with the recommended one instead!