Cleaning a 12v Supply

Hi everyone, I'm going to use an Arduino Uno 3 in my car and have decided to use a buck converter to regulate the cars power for my arduino. I understand that this will give me the output I need from 12v to 7v, but what are my options in cleaning the power? I'm just worried if I have a dirty/noisy supply that it will affect the arduino and the sensors attached to it (MAP boost sensor and a thermocouple) so I was thinking I need some sort of in-line filter coming from the cars battery to the buck converter. Or would it be better to use it in between the buck converter and the Arduino?

A filter I have found: http://www.jaycar.com.au/productView.asp?ID=AA3074

Or if anyone has any suggestions I would appreciate them.

Cheers Mitch

the battery 12v does ok as a filter for the alternator, a couple of caps an inductor coil, a linear regulator...

i've had all my circuits run fine from a car without much issue (but they were not sensitive to emi unlike logic ic's) ....

The buck converter will have a small capacitor in front of it. But you may want to "clean" the output of the buck converter if the ripple/noise is too high to your taste. I don't know which buck converter you're using. Some buck converters have built-in linear regulators at their output. Others don't have.

Of course, you can add your own linear regulator to your DC/DC converter's output. By using a post-linear regulator at the outputs of your DC/DC converter, you can bring down ripple/noise to 10mV peak to peak.

vasquo:
The buck converter will have a small capacitor in front of it. But you may want to "clean" the output of the buck converter if the ripple/noise is too high to your taste. I don't know which buck converter you're using. Some buck converters have built-in linear regulators at their output. Others don't have.

Of course, you can add your own linear regulator to your DC/DC converter's output. By using a post-linear regulator at the outputs of your DC/DC converter, you can bring down ripple/noise to 10mV peak to peak.

Hi Vasquo, thanks for the reply,

the buck converter I was thinking of using is this item here: http://www.ebay.com.au/itm/DC-DC-Buck-Converter-Module-LM2596-Breadboard-Power-Module-1-23V-35V-/221204735159?pt=LH_DefaultDomain_0&hash=item3380d464b7&_uhb=1

It says 30mV MAX output ripple, would this affect the arduino? Do you think this buck converter would be any good? Or do you know a better item I could use?

Thanks for the help. Mitch.

My "beef" with Chinese PSUs is they say one thing, but actually do another. So I'd say test and verify that it's true.
They may say 30mV, but does it really measure 30mV on your scope?

If it's really 30mV, then it's probably going to be fine.

UPDATE: I did a quick check on the 2596 datasheet, and typical performance graphs show ripple is 50mV-100mV. How can they claim 30mV, better than the datasheet? As I said... test and verify. Don't trust those lying chinese. Maybe that 30mV is for a no-load condition.

Hi, The other thing to consider is high transient voltages that occur when the car is started and the starter motor is switched OFF. Often called "Load Dump" transients.

There's a lot of energy stored in the magnetic field of the starter motor windings. It WILL go somewhere. It can damage electronics.

See: Load dump - Wikipedia

Also some info here: spike protection in automotive applications??? - Circuit design - Eng-Tips

Thanks for the replys, Vasquo I have found another unit with even lower output ripple - 7mV http://www.ebay.com.au/itm/DC-DC-Adjustable-Buck-Converter-Step-down-Voltage-Switch-power-supply-module-/171019449097?pt=AU_B_I_Electrical_Test_Equipment&hash=item27d18db309&_uhb=1.

But like you say they might be quoting it with no load. I will test it when I get one to make sure.

Terryking, thats another thing to worry about. There is a fair bit of talk about using a tranzorb... Everything ive read about how to protect my circuits says to use tranzorbs, diodes, resistors etc but I can never find information on how to correctly incorporate it all.