power supply, I have only common cathode diodes

[stefon]

stupid question... I have only common cathode diodes schottky diodes.

Can I do something like that to get symmetrical power supply?

[MagicSmoker]

You sure can.

[stefon]

well, this is how it looks... "-" is weird... why?



edit: OK, I think I know.... reverse voltage of one schottky diode is only 30V and when I connected both 12V trafos, there is 40V peak to peak

[StillTrying]

edit: OK, I think I know.... reverse voltage of one schottky diode is only 30V and when I connected both 12V trafos, there is 40V peak to peak

Looking at the scope that explanation doesn't make sense to me, but I can't explain why just 1 half of the  -ve's cycles is floating about either.

[Jwillis]

Looks like you have one bad diode that isn't recovering very well.

[ArthurDent]

If the circuit is as shown and you have no real load, it may just be reverse leakage on one diode. Try just touching a 1K resistor across the output and see if the waveform returns to normal. The circuit may work just fine with a normal load but the scope you're using may be very high impedance and the diode has enough reverse leakage to show some voltage at this really low current load. I would still check to see which diode is causing this and perhaps replace it if you have spares, just in case.

https://www.tutorialspoint.com/semiconductor_devices/semiconductor_devices_leakage_current.htm

[schmitt trigger]

  What ArthurDent said

[andy3055]

stupid question... I have only common cathode diodes schottky diodes.

Can I do something like that to get symmetrical power supply?

If you need -ve voltage, should you not reverse the diodes in the bottom half of the circuit?

[StillTrying]

I think it's more to do with capacitance across the transformer windings rather than anything to do with one of the diodes.
A small load, even ~10k across the rectified -ve supply's DC output would probably fix it.