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Old 12th September 2013, 07:51 PM   #1
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Default Bipolar ps from single ended transformer

This may be a bit of a unique problem (I searched and couldn't find anything similar), but I am trying to recycle parts of an old Dynaco 120. The power transformer has ~72 V secondary (no center tap). I would like to create a +/- 38V PS (or thereabouts). This obviously includes the creation of a floating ground. I have seen examples of this being done, but not at the volts or amps I envision. Can anyone help with a diagram or suggestions?
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Old 12th September 2013, 08:19 PM   #2
FoMoCo is offline FoMoCo  United States
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The virtual ground can be done, but it'd be terribly inefficient and cost more than a new transformer. Another choice could be a half-wave rectifier with small caps, and a metric buttload of ripple, feeding regulators. Again, the same disadvantages apply.

Bottom Line: If you need more than milliamps, use a different transformer.
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Old 13th September 2013, 08:32 AM   #3
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by dmtparker View Post
I would like to create a +/- 38V PS (or thereabouts). This obviously includes the creation of a floating ground.
It depends very much on the ground current you intend to draw.
If the loads are mostly balanced, as in an amplifier, you could use a Quad style solution:
Virtual ground in power amp applications
If you need more current, you can use a solution like this one: Dual polarity power supply with a single secondary transformer? (or use it to supplement and help the Quad virtual ground).

For really high currents, it is still possible to get a good efficiency, at the cost of some complexity: Hex Buffer, MOSFETs Build A High-Power, Lossless, Virtual Ground | Power content from Electronic Design
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Old 13th September 2013, 09:06 AM   #4
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Virtual ground in power amp applications as in the Quad 606 is perfect for balanced amplifiers and has been in use for years and years. The current is only a problem if the low frequency output of the amplifier is not handled by the smoothing capacitors. There are no other disadvantages that come to mind except the virtual ground should be established before the speakers get any load either through soft start or a basic relay on a resistor/capacitor 1/2 second or so timer. This will stop any instability at power on.
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Old 13th September 2013, 01:16 PM   #5
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Smile Solutions found!

Quote:
Originally Posted by Elvee View Post
It depends very much on the ground current you intend to draw.
If the loads are mostly balanced, as in an amplifier, you could use a Quad style solution:
Virtual ground in power amp applications
If you need more current, you can use a solution like this one: Dual polarity power supply with a single secondary transformer? (or use it to supplement and help the Quad virtual ground).

For really high currents, it is still possible to get a good efficiency, at the cost of some complexity: Hex Buffer, MOSFETs Build A High-Power, Lossless, Virtual Ground | Power content from Electronic Design
THANKS! This is exactly what I was looking for - I never thought to search on "virtual ground" - duh.
As I digest these solutions, I may have more questions, but this looks like a great start.
Thanks again
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