The two diodes, lift the ground pin to 1.4V, because the regulator keeps the output 12V above the ground terminal, the output is 12 + 1.4V = 13.4V above 0V. I personally wouldn't bother with this circuit, I'd use an LM317 with the correct resistors values to give 13.4V.
bananasiong said:
The waveform I've seen is just a flat line (but not nothing as I mentioned previously). I didn't put any load to it, I thought I can see the charging and discharging waveform.
How can you see a charging and discharging waveform with no load?
There is nothing to discharge the capacitor, so all you'll see is the charging waveform, consisting of a fairly fast voltage increase followed by a straight DC line, you probably only noticed the latter because the first event was too fast for you to see.
A load can be just a resistor right? Then the load current should be V/R.
A resistor will create less ripple than a regulator, because the current drawn will reduce when the voltage falls while a linear regulator draws the same current for a given load regardless of the input voltage.
The best dummy load for your rectifier is an LM317 constant current source, the circuit is on the datasheet.
I'll try it tomorrow, the lab is not opening just for me on Sunday
You have access to a lab?
Do you do your experiments at work, like I do?