Having just built your new masterpiece, it is usually with great trepidation that one applies power. There are few things quite so disheartening as seeing your creation "go up in smoke" just because of a simple mistake.
http://sound.westhost.com/project44.htm
Using the versatile L200 voltage regulator, this power supply has independent voltage and current limits. The mains transformer has a 12volt, 2 amp rated secondary, the primary winding should equal the electricity supply in your country, which is 240V here in the UK.
http://www.mitedu.freeserve.co.uk/Circuits/Power/l200var.html
The circuits shown are based on the LM339 Quad Voltage Comparator chip or the LM393 Dual Voltage Comparator chip. These devices are functionally identical. The LM311 Voltage Comparator can be used for these applications as well and also has a number of unique features.
http://home.cogeco.ca/~rpaisley4/Comparators.html
This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range.
http://www.discovercircuits.com/DJ-Circuits/pwrboost.htm
AC signals can emanate from many sources, and many of these sources are incompatible with the most popular interface voltages, such as TTL.
http://www.edn.com/article/CA307868.html
This circuit may be used up to 40 volts.
http://www.jensen-transformers.com/as/as079.pdf