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Switched Regulator, Frequency settings

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luiHS:
 
Hello.
I am using recently the LM25085, to replace the XL4015 and XL4016.

I only have a problem. At 12v input, the voltmeter of the power supply varies constantly and rapidly (mA and tenths of mA). If I raise the voltage to 18v that problem ends. In addition, to 12v, approaching the ear to the circuit you hear a hum or continuous beep.

I put the oscilloscope and I see a signal of about 400Hz mixed with the DC, it is very dim but it affects the circuits that I connect the regulator.

I used the Texas configurator, which works quite badly because every time you enter, with the same configuration, it gives you different values ​​for the input capacitor, even for another circuit capacitor. According to the configurator, for the frequency I selected (the one offered by default) I was instructed to put a 15uF capacitor, but I finally put 3 x 10uF in parallel. But sometimes you go into the configurator, and it tells you to put 3 x 15uF (in parallel I understand), if this is the right thing, my 30uF could be the problem.

Is it possible that the malfunction is due to the low capacitance of the input capacitor? I have thought of putting another two or three capacitors of 10uF in parallel, to rise to 50 or 60uF.

On the other hand, I thought about raising the frequency of the oscillator to 700 or 800Khz, so the inductor will be much smaller and cheap, and I could put it on a Reel in my Pick and Place machine.

What advantages and disadvantages does the oscillator of a switched regulator have to work at a higher frequency? As advantages I see that the inductor is smaller, of value and size, also cheaper if the size is reduced.

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