Circuit Project Electronic

This power supply is not designed to use the prefabricated IC voltage regulators, even though such regulators do exist. The 7812 and 7912 ICs are quite capable of providing regulated +12 volt and -12 volt outputs, respectively. However, we have two problems with doing it this way. First, each regulator provides an output voltage accurate to within 5%. For a 12 volt supply, this allows a ±0.6 volt variation. That’s not bad, but we’d like something a bit more accurate for our purposes. Even more important, however, is the fact that the 7912 and the 7812 are not in any way guaranteed to mirror each other. We could easily have +12.5 volts and -11.5 volts as power supplies, and we want to avoid this disparity if we can. Besides, we’d like to easily switch between ±12 volts and ±15 volts, and still keep the output voltages accurate. That’s a bit more complex with these ICs. (Plus, we’d like to use op amps for the purpose so we can demonstrate a very practical application for op amps.)

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Read More Source:
http://www.play-hookey.com/analog/experiments/
plus_12_volt_ps.html
Thank you.