"5V" Voltage level on UDB5mini and UDB6mini

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ben levitt

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Oct 19, 2020, 1:58:55 PM10/19/20
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Hi UDB'ers,

Working with Bill and Guy, we noticed that the LDO 5V regulator on the UDB5mini and UDB6mini have a bit more voltage dropout under load that I had at first thought.  With a standard setup, this regulator only supplies the GPS.  Under load from the GPS units that most of us are using, and assuming that the UDB board's VCC is powered with 5V, the "5V" rail for the GPS is dropping to about 3.8V.  This is as opposed to about 4.5V on the original UDB5 boards.  Fortunately, the recommended GPS units are all quite happy running at this voltage, or even lower.  We've tested the EM506, and the uBlox M8 line extensively, and their performance is the same at 3.8V as when powered at 5V.  So if you're using one of those, or anything else that's happy at 3.8V, then all is well!  I've been flying only planes using the UDB5mini and UDB6mini for over 3 years, and my EM506 and 3 uBlox M8Q units have all been working beautifully.

The issue was spotted because Guy is using a different GPS module that expects a full 5V, and it was not functioning properly.  If you find yourself in a similar situation, here are some options you can consider to work around the issue:

1. Switch to a GPS that is happy at 3.8V.

2. Power the UDB5/6mini's VCC with a higher voltage (VCC at 6.2V will get the "5V" rail up to a true 5V.)  Just make sure that if you have VCC and the servo rail tied together, that your servos can handle the higher voltage.

3. If your VCC is a stable 5V, you can tie VCC to the "5V" rail to bypass the 5V regulator.  One easy way to do this is to connect the pin labeled 5V (next to the programming port) to one of the VCC pins.

Best wishes, and safe and happy flying to you all,
Ben

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