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In Reply to: RE: Dual B+ froma a CT tranny? posted by jorisdallaire on October 17, 2014 at 14:21:52
Easier to make a bipolar supply with one bridge and two capacitors; it has a half-voltage tap automatically.
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That would give him a positive and negative supply but he's looking for two B+ supplies. It looks like one for the output and one for the driver stage.
So ground the negative output instead of the center tap. :^) It's what you would do anyhow with a single fullwave bridge. By splitting the usual capacitor into two in series, connected to the transformer CT, you get an independent source of half the voltage. If you don't want exactly half the voltage, make one of them a choke-input stage. It's really very flexible.
Hi Paul.
I've never tried this mainly because it never occurred to me that you could get two positive voltages off a bridge by inverting the negative connection with a center tapped transformer.
Is it really that easy? Is the grounding correct for the circuit?
Nothing is "really that easy"!
The circuit does not care what terminal you call ground.
However, if you have a transformer designed specifically for the traditional FWCT circuit, and use it with a FW bridge, the transformer terminals will see twice the voltage they were designed for. If the voltages are high then you may exceed the specs of the transformer and get arcing, corona, and other HV issues. I have no knowledge of whether some or all or none of the manufacturers take this into account, it's just a theoretical issue for me.
And probably will give it a try. I'll set series resistors to balance the caps' voltages vs the current draw of each stage. The regulators will provide the fine adjustment.
Paul, let me take this moment to thank you for all the help you gave to me on this forum and i am sure i speak in the name of others. You could as well concentrate your efforts exclusively to the Bottlehead forums, yet you find time to spend with us inmates :-) I salute your dedication to the hobby.
Of course this doesn't devaluate the contribution of the numerous kind people who helped me over the years - there are so many resourceful people here!
Regards,
Joris.
"he's looking for two B+ supplies. It looks like one for the output and one for the driver stage."
Exactly. I'll have regulators for each stage, so i could drop the input stage's B+ from the output's. But the goal here is to try to reduce wasted power, as the voltages are quite far apart (500v vs 200v).
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