The 7815 is an integrated voltage regulator with three terminal fixed positive 12V inputs. The 7815 pin diagram is shown below.
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7815 Main parameters are: output DC voltage U0 = +15V, output current L:0.1A, M:0.5A, voltage adjustment rate 10mV\/V, output resistance R0 = 0.15Ω, input voltage UI range 18 ~ 20V. Because the general UI is 3 to 5V larger than U0, in order to ensure that the integrated regulator works in the linear region.