I am having an issue running an Arduino (requiring a 3.3V power input) from a 21V AC circuit. The input of the circuit is from a doorbell transformer and provides 21V AC. Then the AC input passes through a bridge rectifier to produce a DC output (of about 26V). The output from the bridge rectifier is smoothed with a capacitor, and then a voltage rectifier converts the ~26V input into 3.3V output for the Arduino.
However, this circuit has an issue I am having trouble figuring out. Measuring the output of the 3.3V voltage regulator reveals that it is, in fact, outputting 3.3V as expected. However, the Arduino seems to reset itself over and over.
My working theory at this point is that the issue has something to do with the connection to ground. If I disconnect the AC input and replace the 3.3V regulator with an external, regulated 3.3V supply, the system works fine.
I would greatly appreciate any help you could provide with diagnosing the issue with this circuit design.