The advantage of the universal transformer circuit is that it allows switching to either 120v or 220v primary operation. The dual secondaries can be configured to use separately, in series or in parallel. In this case the secondaries are setup in parallel to provide an RMS output value of 12.6 volts AC.
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The Bridge Rectifier circuit, comprised of diodes D1 thru D4, provides a means for converting the incoming AC to pulsating DC.
The Pulsating DC from a rectifier circuit generally requires a means of smoothing out the voltage. One of the most common ways to filter/regulate voltage is to use one
of the 7800 (positive) or 7900 (negative) series three terminal regulator integrated circuits. These circuits only require a couple of capacitors, one to filter out the low frequency component and one to eliminate any high frequencies. The IC maintains a constant DC output voltage regardless of any variations in input level.
To operate properly the input needs to be two or three volts higher than the desired regulated output.
Part# | 7805 | 7806 | 7808 | 7809 | 7810 | 7812 | 7815 | 7818 | 7824 |
V out | 5 | 6 | 8 | 9 | 10 | 12 | 15 | 18 | 24 |
