Question about Vehicle Electrical system and electronics

Hi, I'm working on a prototype controller for vehicles, mainly a retrofit system for hot rods and custom vehicles. it will have many features, some of which I have already designed and am working the bugs out on. My main focus right now is power source. as many people know, vehicle electrical systems (especially in older systems) are very harsh. Voltage spikes can go as high as 40 volts for about 4 milliseconds, drops in voltages during starting and low battery, EMI from the ignition system, A bad regulator could also be an issue. I need to provide protection from these issue. I know from experience that a simple system of capacitors, diodes, and Coils can help to almost eliminate any noise and ripples. A good voltage regulator circuit will help to keep the voltages level. the issue is with the voltage spikes. Even when they only happen for short periods of time it is enough to damage components. I need a way to suppress transient voltages, I have found TVS diodes at mouser and such but I have no idea what I'm looking for. I have been over this article a few times,http://www.industrologic.com/autotransients.pdf but understanding it is another problem. I'd like to see what opinions others here have. a few things to keep in mind. A) Needs to be able to provide 5 volts 500ma, and 12 volts 2 amps. B) Needs to be able to be built on-board, I do not Want an external device or a pre-built board. C) Components that are through hole and not surface mounted are preferred for the prototyping stage, as most of my stuff is bread boarded before being soldered.

Whatever opinions would be great.

My other question is about LEDs and automotive power. I have a lot of retrofit LED lamps for the truck. most of them have warnings about over voltage and life expectancy. All i really see in them is a diode and a resistor. Should I create a power supply to regulate the power for these as well or is it really not much of a concern?

Because of your current demands, a switching regulator would be best, but if you need a clean supply it might be worth passing the switched output to a power transistor and a couple of caps, or a 78xx regulator...

Easier to ask what you have in mind.

cjdelphi: Easier to ask what you have in mind.

Agreed, I was thinking about a circuit that look like this

Voltage in + ----Diode---Zener Diode--Coil--Capacitor-----to voltage regulators | | | TVS diode Capacitor Capacitor | | | Voltage in - ----Diode---Zener Diode--Coil--Capacitor-----Ground in circuits

if that makes any sense, I wish I had a better way to draw it out but i don't have a good program to illustrate with.

The voltage regulator circuits would consist of standard 7805 and 7812 regulators, 2 of each. I also have some larger variations of these that are rated at 2 amps instead of just 1 amp. heat sinking will be used, the case i have is one giant heat sink. I'm wanting a lot of head room for expansion.

I'm guessing something a little more advanced might be needed though?

The 12V output doesn't leave much room for regulation : charging batteries should be about 13.6...13.8V. (Does your 12V application need to be accurate? If not, a simple inductor and cap should suffice to reduce noise; you could add a 12V zener.) For the 5V part I would go 78L05 with sufficient caps (electrolytic, perhaps 100uF and 0.1uF in parallel, to help stop noise spikes) on both in- and output, and even a series inductor at the front (with some caps on both sides). You would only need one of each circuit per 12V & 5V in the +ve leg/s only, not 2 as I think you meant in your description.

TVS's are excellent protection against spikes. You want to choose ones that are set to breakdown (see the data sheet, this is not a failure) at just above your regulated voltage, so if you have a 12V supply, you want it to be designed for 14-15 V (Or lower if your equipment is sensitive to overvoltage). People use these for ESD protection as well, which can be severe overvoltage, so its not too bad. Zeners are good for crude regulation/voltage setting. Additionally adding both a large (Depending on your application 5-1000uF) and small (1-10nF) bypass caps across both the inputs and outputs of your regulator will help immensely. The big one keeps the voltage stable and the little one will help absorb fast spikes.

Another really big issue will be radiated noise getting into your circuit. If possible design your PCB board with a ground plane, use shielded cable (And ground the shield to the chassis, or other similar point), and follow good grounding rules. This should minimize the issue.

The Atmel site has a ton of documentation on automotive circuits, but one that you might find helpful is this one:

http://www.atmel.com/images/doc1619.pdf

"AVR040: EMC Design Considerations"

It will at least give you enough information so that you can make a robust power supply for an automotive environment; I should also note that Atmel makes automotive-grade versions of the microcontrollers used by the Arduino platform - these might be worth looking into as well.

cr0sh:
Atmel makes automotive-grade versions of the microcontrollers used by the Arduino platform - these might be worth looking into as well.

This is something I did not know. Thank you, I will look into it for sure. for now though I have a stock pile or standard atmel chips, several ATtiny of different kinds, and several 328Ps. I’ve been looking for a more robust version of the Tiny and 328.