Max power voltage?



  • Re: Max power voltage?

    I tried with the Pololu, powering the lopy directly on the 3V3 pin and the result is the internal DC-DC converter fried. So I broke the LoPy.
    For solve the problem I removed all the powering circuit on the LoPy (U5 T1 L2).

    link text



  • @Officina I just tried running the device with 3.3 V on Vin, and it works. At the moment, the DC in is at 2.95 V, and still running. According to the data sheet of the regulator, it goes into a bypass mode if the input voltage is too low, and that's what I wanted to confirm.
    So it looks as if is more safe to run with a low Voltage on Vin.



  • @Officina
    Then better use OEM modules
    https://www.pycom.io/webshop#oem-products
    they do not include Voltage regulator and many other things



  • @robert-hh but I have a 6V solar panel that can be 7V in direct sun illumination. For me is not a good idea use two dc-dc converter for powering a pycom, one from 7V to 5V and the internal one from 5V to 3v3



  • @daniel: reading this experience and that of some other user, the note about using the 3.3v as power input seems not appropriate. instead, you should declare it as output only.



  • @livius I have the same issue on 4 pycom ( 3 lopy and 1 sipy), so I removed all the regulators.
    On the lopy with regulator and powering on 3v3 the drain was about 100mA without anything running, and on sipy 2A.



  • @Officina
    Good to hear that board is ok - with only regulator removed :)



  • @robert-hh without U5 T1 L2 and power on 3v3 is working good. In deepsleep mode without any sensors is 2.77mA and in lora TX about 130-140mA (wifi and BT disabled)



  • @Officina There were other people who also had problems in driving the device from the 3.3V Pin. Since that is intended as output, I personally was always skeptic about powering by the 3.3V Pin. Is the Lopy now still working, when supplied through the 3.3 V Pin?

    P.S. There is a Pololu device variant which has an variable output, which uses the same PCB as yours, just with a potentiometer soldered to the three pad at the end of the PCB. Even with your device, you could change the voltage by adding a resistor to the middle and one of the end pads.



  • Yes, I used this one:
    link text



  • @Officina
    On 3V3 pin you must have exactly 3V3 regulated and ripple free.
    On 5V pin you can have max 5V5 but documentation for LM3281 state absolute maximum 6V


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