Use 7812 to make a positive 12V DC power supply
Is 220V AC voltage correction 12V
If the transformer secondary symmetrical center tap, with full-wave rectification, then the secondary voltage can also be set lower, 11.5V ~ 12V can be.
The secondary voltage of the transformer is preferably set to about 12.5V. Because 12.5V sine wave AC voltage peak is 17.6V, after the bridge rectification after 15.2V ~ 15.4V, and 7812 instability voltage is 2V, generally leave about 1V margin is about 3V more appropriate. If the transformer secondary voltage is set to 16V, the peak is 22.6V, after the bridge rectifier over 20V, 7812 to dissipate the power of 8V × output current, when the current reaches the rated 1A, 7812 own power consumption More than 8W, will be very hot, and may even be damaged due to overheating.
1st floor ny_peter circuit diagram is basically correct, but the transformer secondary voltage setting is too high, which will make the power efficiency is low, in the larger output current regulator serious heat.
