This simple circuit provides a symmetrical power supply derived from the AC output of a transformer's secondary winding without center tap. It is very useful in applications
where both positive and negative lines are needed but a center tapped transformer is not available.
The circuit is basically made of a bridge rectifier with additional components that function as the negative line. Take note however that this negative line can deliver less current than the positive line.
The resistors R1 and R2 are initial loads. They are added to make sure that the negative line is active even if the circuit has no load attached to its output lines. This trick is applied here because, otherwise,
no negative output will be produced when the positive line has no load. In case you need the negative line to deliver more current than the positive line, just reverse the circuit.
To do this, just reverse the polarities of all diodes and electrolytic capacitors. It means all diodes and electrolytic caps, no exemption.
The bridge rectifier will deliver more power in the negative line in such case.
The actual circuit can handle AC inputs up to a maximum of 18 volts AC. If you need a higher voltage level, change the voltage ratings of the diodes and capacitors to
at least the double of the maximum AC input voltage.
To select the correct diodes, see the appropriate table at the end pages of this book.
Parts Placement Layout
External Wiring Layout
Electronic Circuits volume 1.0 - Circuit Nr. 59
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
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