| Electronics > Projects, Designs, and Technical Stuff |
| Power supply transformer connections |
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| MarkF:
This is an old transformer I was going to use. My project needs +/-12V and 5V. The 500mA is probably twice the actual load. If that. Maybe I can just use two full wave bridges on a PCB I did. |
| MarkF:
Here is the original circuit I was trying to adapt. I thought it was using a full wave bridge. After closer inspection, it is not. |
| Ian.M:
Your transformer's 7.7V-0-7.7V winding + a bridge rectifier and two resevoir caps between bridge + and winding CT, and CT and - can feed your +5V (from CT) and +12V regulators reasonably efficiently, and use the 14.4V winding + another bridge and reservoir cap to feed the -12V regulator. |
| MarkF:
Will the 5V regulator input be halfwave rectified then? |
| Ian.M:
Nope. Full wave. Consider the CT as ground and you'll see that both the bridge + and - have equal and opposite full wave rectified voltages. Now consider output 0V (bridge -) as ground and you'll see that the +12V regulator gets the full wave rectified whole winding voltage and the CT provides the 5V regulator with half of that so neither should run excessively hot. |
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