Zener diode in PIXHawk

   On the power connection page, it is suggested that we use zener diode for protection when using back up power supply. The connection suggested is to connect zener across the +5v and GND of the servo rails directly.

3691142342?profile=original

http://plane.ardupilot.com/wiki/common-pixhawk-wiring-and-quick-start/

 

   However when I read about zener diode, then the circuit to control voltage is suggested as follows.

 3691142409?profile=original

  Notice the resistor in series with the zener.  I understand that this resistor will consume the voltage which is excess to the required voltage. However in the connection suggested for PXHawk, there is no resistor.  In this case how is it able to regulate the voltage? My knowledge of electronics is limited, so I would appreciate an explanation of this.

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –

Replies

  • Hello,  I'm installing a zener diode with a capacitor in parallel for a Pixhawk application with a 5V 5A UBEC.  Would appreciate some advice on capacitor size.  I have the option of using a 220 microfarad, a 330 microfarad and a 100 microfarad capacitor (all rated at 10V or greater).  Will the 100 microfarad capacitor by suitable or should it be larger capacity?  The 100 is really convenient because of its small size - about the size of the zener.

    Advice would be appreciated.  Thank you

  • Hi guys,

    Is this a suitable capacitor to use in parallel with the zener?

    https://www.elfaelektronikk.no/elfa3~no_no/elfa/init.do?init=2&...

    Cheers,

    Sandy

  • In relation to this..


    http://plane.ardupilot.com/wiki/common-pixhawk-overview/#Powering
    "To complement the diode, it is also useful to add a capacitorin parallel to the diode. The capacitor will smooth out eventual voltage ripples. As advised for the diode, the capacitor should be connected with as short wires as possible. Do not oversize the capacitor."

    1) what is the recommended capacitory?  Will a 25v 1000uf work or is that 'oversized'?


    2) How do we parallel it.. should it be done this way?

    --------(+)-----/[capacitor]----/[zener diode with rev polarity]
    --------(-)------/------------------/

    or this way:

    --------(+)-----/[zener diode with rev polarity]----/[capacitor]
    --------(-)------/-------------------------------------------/

    thanks for the help!

    • I use a 6.3V 200uF capacitor.

      Actually, in my case when using a redundant backup 5V supply to power the ESC output rail, my PixHawk will only boot with the capacitor added.

      If I don't use a capacitor, the Pixhawk just makes cricket-like sounds with crazy flashing of the LEDs instead of booting. See it happen after 40secs here:

      https://www.youtube.com/watch?v=jODj9UzkG1Q

      I suspect that it has something to do with the sequence in which voltage rises at the power module input and the ESC connector during power up, and the power selection mechanism in the Pixhawk.

      The capacitor in my case, serves to slow the down the initial voltage rise at the ESC input.

      I've reported it a month ago to 3DR support, but haven't heard anything of it since.

      • Hi,

        I have the same issue on my Tricopter, I've had to power the servo rail via an external BEC.  Cant explain why the BEC from the ESC is not liked yet the external one is all good.

        I've tried a 200uf capacitor but it didnt work.  I tried them 2 in parallel (for 400uf) and it didn't work, did you get a resolution in the end?

        Chris

      • thanks.. may I know how you soldered it up? is it this way:


        A) capacitor then zener in reverse

        --------(+)-----/[capacitor]----/[zener diode with rev polarity]

        --------(-)------/------------------/


        B) zener in reverse then capacitor


        --------(+)-----/[zener diode with rev polarity]----/[capacitor]
        --------(-)------/-------------------------------------------/


        thanks in advance!

        • If I'm interpreting your ASCII art correctly, then B makes no sense, because either your circuit is open, or you want to use the capacitor in series.

          The capacitor must be connected in parallel, so it doesn't even matter in which ESC/servo plug you stick it. You can make one plug for the zener diode as shown in the documentation, and another one for the capacitor.

          The only reason I'm even using a capacitor is simply to make it boot. Otherwise I wouldn't even bother, because I don't have noisy equipment connected to my Pixhawk. My ESCs are opto isolated too, so it's as clean as can be.

          • Actually, A or B will work:

            http://ardupilot.com/forum/viewtopic.php?f=21&t=6463&start=20

            file.php?id=1820&mode=view

          • *slap on forehead*  =)  thanks for taking time to clarify that! I've been searching exactly what it means  by 'parallel' and I just never thought of doing it in a separate servo lead! 

  • I just want to point out a mistake in the photo of the servo connector: it shows that the diode is connected between positive and signal, instead of ground.

    You can probably flip a JR connector around in the pixhawk, so for safety sake, I'd recommend using a Futaba connector and the diode in the correct pins.

This reply was deleted.

Activity