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Powering the 7805 from the 7815 will distribute the thermal loss of the 5V output between the two regulators but the total thermal loss will be the same, not less.One simple idea would be to create the above circuit (corrected) twice.
One with a 7805 for 5V output and one with a 7815 for 15V output.
Depending on your current needs, you may even get away powering the 7805 from the 7815, for less thermal losses.
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You might want to add de-coupling caps to both outputs as well as a small load, say, 1K for the 7805 and 3.3K for the 7815 (≈5ma).This circuit will be right to power PIc and LM1893??
View attachment 72744
Powering the 7805 from the 7815 will distribute the thermal loss of the 5V output between the two regulators but the total thermal loss will be the same, not less.
National Semi produced most LMxxxx ICs for many years.i have found LM1893 and it stays existing and products by Texas instrument
i have buy it
one problem i have with the pin 5 ??
how to have 1 logic for Tx and 0 logic for Rx. i link it with pic ??