| Electronics > Projects, Designs, and Technical Stuff |
| Switched Regulator, Frequency settings |
| (1/1) |
| 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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