Buck Regulator Supply From Multiple Sources

Question

Hey Electrical Engineerers!

I am currently working on making an LED tail light for an older car.

Overview of the Taillight

Each tail light has 4 inputs connected to it: Park, Brake, Turn, and Reverse.
The 4 inputs are switched 12V. For example, if you engage your turn signal, the turn input will switch 12V on and off each time the blinker or hazard lights are activated. The most current this circuit could draw is ~2.5A.

When I initially created this circuit, I had a regulator on each of the inputs. Soon after, I realized that four regulators was much too expensive. So with that, I created this circuit which aggregates all the power to one buck regulator (LM2596) and uses MOSFET transistors to determine which light should be on.

NOTE: The LEDs for each light are actually an array of LEDs, but I simplified it to just one for this schematic.

Circuit

Questions

1. Is this an effective circuit, specifically the one regulator being supplied from multiple sources and the MOSFETs being used to switch on the lights? Is something like this available in an IC?
2. I would like to add over-voltage and current protection to this circuit, how could I effectively do that?

Thanks in advance, I really appreciate any feedback.

Answer 1

As Dave Tweed pointed out, the logic will be wrong the way you drew it. Suggest adding a TVS and fuse on the input to protect the regulator and wiring. Use 200V or higher ordinary diodes (eg. 1N4004) for your input 'or' gate. Consider adding a small series fusible resistor before the TVS to help it clamp. This is 'low side' switching so you need to provide a return wire for the lights rather than the chassis. To make high side switches requires another transistor for each LED bank.

You do need to protect the MOSFET gates and probably to provide some kind of pull-down. Something like this:

^{simulate this circuit – Schematic created using CircuitLab}

Resistors can be 1/4-W 5%.

If the lights are also connected to a computer or something to indicate bulb failure you may have strange things happening (this stuff started in the 1980s so the car could still be plenty old).

Answer 2

Your mosfets should be N channel and logic level so when the drive signal is active 12V logic high the relevant lamp is on .Gate protection like Spehro stated is essential.R2 can be 10K if R1 is kept at 1K .Remember that the incoming logic is active high not active low .Your off the shelf IC circuit makes a fixed output voltage which has to be greater than the LED drop .Say if one of your lamps in the LED cluster is White and has a terminal voltage of say 3V and you set up your chip to 4V DC then your overall efficiency is only 75% of what the IC is .Now lets say that one of the LEDs is red and drops 2V then your overall efficiency wont get to 50% .If you set up a switchmode buck current source then the power would not be wasted in the resistors.The current setting can be steered to different values for different coloured lamps with the mosfets.