I'm powering a 12 V computer fan with a simple 7810 circuit shown here:
When the fan is connected to the regulator, on the output I get this wave:
When I zoom out in time, I get something that looks like this:
For those who can't be bothered to click on the image, the distance between the peaks is almost 10 ms.
When I zoom out a bit more, I can see that there is another wave here riding on top of those peaks like this:
The higher top peaks have peak voltage of 13.4 V and the lower peaks are 12 V. The peaks on the bottom side which go together with 12 V peaks are 8.8 V and the bottom peaks of 13.4 V top peaks are 8.6 V.
So any ideas what could be causing this?
Here's the input waveform with the output peaks:
The input peaks are 10 ms apart and are in phase with AC line transitions, as expected since the AC frequency here is 50 Hz. The input is coming from a diode bridge rectifier. The input voltage is a bit high since I changed the original 1N4007 diodes with STPS2H100 Schottky diodes because I initially believed that one of the input diodes developed a short.
I can't determine the exact relationship between the input and output wave. When I trigger by one of the waves, the other is flowing from left to right on the screen.