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I have a centre tap transformer 240V – 24V @ 250mA. I know I will get 12V between the centre tap and either of the other connections (I think one will be -12V), but will I have two 12V supplies at 250mA or 125mA? And will the 24V supply be 250mA?

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Each half can still supply 250mA. So you 2 12V outputs @250mA.

A common way to use a center tap transformer is to provide postive and negative supplies with 4 diodes.

Be careful about using a bridge rectifier from each half as I see in some circuits, that won't work as some of the diodes short out others.

The total power output depends upon how the transformer was rated but it probably is good for 250mA DC output from each of the positive and negative supplies.

Dual output supply

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  • \$\begingroup\$ If I ignore the centre tap and just use the two other connections will I get 24V and will it be 250mA? \$\endgroup\$ – David Morse Aug 24 '15 at 10:12
  • \$\begingroup\$ You would get 24V between the +12 and -12 outputs in Kevin's answer, but with the regulators, that circuit still needs the centertap common internally. What you cannot do is draw 250ma from say the 12V output in Kevin White's circuit, and simultaneously draw 24mA from the overall 24V. \$\endgroup\$ – R Drast Aug 24 '15 at 13:21
  • \$\begingroup\$ You should be able to draw close to 250mA from each supply. It is the same as drawing 250mA from 24v using a bridge rectifier. You only use each winding half of the time for each polarity output. \$\endgroup\$ – Kevin White Aug 24 '15 at 13:56
  • \$\begingroup\$ thanks for the help kevin, are all the capacitors in the above circuit electrolytic? \$\endgroup\$ – David Morse Aug 24 '15 at 15:10
  • \$\begingroup\$ The big values marked with polarity could be aluminum electrolytics. The small values (0.01uF) should be ceramic. \$\endgroup\$ – Kevin White Aug 24 '15 at 16:07

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