Hi, I have a Raspberry Pi with Open Elec installed, which seems to make me a happy media player. So I after being happy with my install, decide to build me a linear supply! Acquired a transformer v-0v-v and with a couple of 5 volt regulators I have built a supply using 1 rail plus centre tap of the transformer and created a supply. I did originally parallel the 2 yellow wires on the transformer to double the current, black being 0 volts, but the transformer started cooking, oops! So I just used one wire and the 0v tap and I got 5 volts for the Pi! Well getting carried away, I built another 5 volt supply for my USB DAC! Great I thought, eager I wired it up, BUZZZZZZZ! 
It only goes away, if, I unplug the feed to the Pi! I used star earth, and just realised I don't have any caps across the 5 volt rails after the Regs, only before! Would having no caps after cause the buzz, or is it because I'm sharing the Centre Tap!
Thanks, Mike
It only goes away, if, I unplug the feed to the Pi! I used star earth, and just realised I don't have any caps across the 5 volt rails after the Regs, only before! Would having no caps after cause the buzz, or is it because I'm sharing the Centre Tap!Thanks, Mike
With CT xfmr 2 diodes make a perfect full-wave rectifier, no need for a bridge.
The two yellow ends of a CT xfrmr are of opposite phase with respect to the CT, so either the upper or the lower diode conducts.
Center tap - Wikipedia, the free encyclopedia
If you don't have 2 separate diodes at hand, it can be done with a bridge, but only one half of it will be active.
The two yellow ends of a CT xfrmr are of opposite phase with respect to the CT, so either the upper or the lower diode conducts.
Center tap - Wikipedia, the free encyclopedia
If you don't have 2 separate diodes at hand, it can be done with a bridge, but only one half of it will be active.
I thought you needed 2 regs because of power consumption and because you wanted to separate the two outputs so that noise / power spikes from one device would not affect the other ... if that's not your concern, just use one, but if you already have them, why not use them.
and that's also the reason why your xfmr cooks when you connect the 2 yellows, thats equivalent to a short.
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