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I have an old honda scooter which has bulbs in all lights. Also, they are driven by AC voltage. I made sequential led indicator circuits(four of them) using 74HC595. The working voltage of the circuit is 5V. The total current draw is less than what the bulbs take. Just that I will have to wire them to get DC from the 12V battery on the scooter. The voltage coming to the terminals of the battery will climb up to ~14V depending upon the RPM of the engine. I already have 7805 regulator and capacitors attached to the circuit. My question is: Is this voltage regulator all I need for the circuit to work without any problem? Or should I add anything additional for the safety of the circuit and the scooter other than fuses?

Vinodvnmy
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    Stepping down 12v to 5v is a lot to ask of from a linear regulator. You need to think about cooling because it probably gets pretty hot during use. – Ron Beyer Mar 01 '20 at 17:03
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    Some regulators are specifically designed for automotive environments. LM283x I think is one such. || Adding 2 series resistors in the 7805 input with a say 9v zener to ground after the first and a cap and a zener of say 7V and cap after 2nd at 7805 input with resistors sized accordingly will (1) Clip most peaks and surges at 1st zener and better again at 2nd before 7805 gets to deal with what is left. (2) reduce dissipation in 7805. || Size resistors to drop max required voltage at Imax. eg say Imax draw is 0.5A. | 1st zener is say 9V. Vmin in is 12V . R = V/I = (12-9)/0.5 = 6 Ohms OR LESS. . – Russell McMahon Mar 03 '20 at 12:50
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    If 2nd zener is 7V then R2 = V/I = (9-7) / 0.5 = 4 Ohms OR LESS. – Russell McMahon Mar 03 '20 at 12:51

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In general that's not enough, and there's too many different "right" ways to do it to go into depth here. Search on "automotive electronics protection circuit" for a start at your reading material. Then come back and ask about specific issues you have.

You need to protect against voltage spikes up to 60V or so (search on "load dump") and reverse voltage (because at some point you will forget and hook something up backward, not to mention that wiring faults can cause reverse-voltage conditions).

Michael Karas
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TimWescott
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  • That is the reason why some standards require the use of keyed connectors and/or different number of contacts whenever the bunch of them meet at the same place, making it impossible to connect backwards or to wrong circuit. The voltage spikes and high voltage drop are real concerns though – Maple Mar 02 '20 at 10:14