Powering Adafruit KB2040

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jensa
 
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Joined: Wed Dec 21, 2011 9:35 pm

Powering Adafruit KB2040

Post by jensa »

Hi,
I just burned up the regulator on my Adafruit KB2040, but I don't quite understand how. I use a TR10S05 to drop from 12V to 5V and feed that to the RAW pin. Ground on the 12V/5V switching supply was connected to the GND pin on the KB2040.

I have two potmeters connected to A0 & A1 and I'm using pins 3 & 5 as PWM outputs. According to the pinout https://learn.adafruit.com/adafruit-kb2040/pinouts & schematic, the RAW pin connects directly to the ap2112K-3.3 input and it's 6.5V max. Given that I'm feeding it 5V, all should be good. Initially, this went well and I got 3.3V on the 3V output pin. I didn't connect anything else to the device, but suddenly the 3V output read 4.2V and the regulator got really hot. Now the power LED does not turn on, so I guess the regulator died.

Never had this happen to me before, but I wanted to know if others have experienced it with these KB2040 boards?

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adafruit_support_mike
 
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Re: Powering Adafruit KB2040

Post by adafruit_support_mike »

That sounds like an issue with the step-down converter. How much output filtering does it have to prevent voltage spikes?

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jensa
 
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Re: Powering Adafruit KB2040

Post by jensa »

Good point. I didn't add any. It has quite a bit builtin, but I guess a 10uf/0.1uF combo on the output would have been in order... Might absolutely be relevant.

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adafruit_support_mike
 
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Re: Powering Adafruit KB2040

Post by adafruit_support_mike »

Yeah.. switchers are inherently noisy. They use voltage spikes to convert one voltage to another.

And for a converter to operate efficently, the spikes have to be as sharp as possible. Any slew in the rising or falling edges becomes heat in the switching mosfets. The major difference in cost and quality of switching converters is the amount of output filtering.

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