Question about SMD voltage regulator to use

For an automotive project i am using a custom 328p project running at 5v. For this i use a voltage regulator to convert the 12-15v down. On my breadboard prototype i use a lm7805. Now i'm thinking about going SMD, i've ordered some lm1117-adj. I should be able to solder a sot-223 by hand. I choose a batch of -adj so i can get any voltage i need in future projects.

But now i also saw other types of regulators, eg. Mic5205. I'm now confused whether i ordered the right parts, there are so many regulators available! Can you help me please?

7805 is the best. Very stable. You can use Regulator LM317 cobine with zenner diode to make output stable at 5V.

gmk05: 7805 is the best. Very stable. You can use Regulator LM317 cobine with zenner diode to make output stable at 5V.

Thank you for your quick response, but as i said in my post lm7805 is too big, and LM317 is also too big (both through-hole). I'm looking for the differences between the SMD regulator types.

remember the power dissipated in the 7805 depends on the current and voltage between pins IN and OUT. Even with 12V IN, there is a 7V voltage drop. The power will be at least P(W) = 7 X I(A) You'll likely have to add a heatsink to the 7805 (or LM317)

maybe you could have a look at the switching regulators, a DC/DC buck converter

Again, thanks but please read my question. I'm looking for advise on SMD regulators. Heat sink will not be an issue, my project uses only about 75-100mA.

Rather than a LM7805, I would suggest that you consider a LDO regulator such as the LM2931. In a car application, this will give you some immunity to the variability in the car's DC voltage. The LM2931 is available in a SOT-263 package, or if you are not drawing too much current, a SOIC-8 package.

http://pages.ebay.com/link/?nav=item.view&id=300782205545

Take a look at those...

The most important spec in an automotive application is the input maximum voltage - expect the car's 12V to have big voltage spikes on it, many LDO regulators have a poor Vin(max) spec and are not suitable. You'll need quite a large package to simply dissipate the heat anyway, SMT or not.

An isolated DC-DC converter is a really good choice and worth thinking about - more tolerant of input voltage variations (high and low), and fail-safe (isolated). Or possibly an in-car USB charger which should provide a clean 5V and not take any space on your circuit board.

RobvdVeer: Again, thanks but please read my question. I'm looking for advise on SMD regulators. Heat sink will not be an issue, my project uses only about 75-100mA.

I DID read your question, and wanted to point out the fact that a 7805 would probably need a heatsink, that's why I suggested DC/DC buck converters ;) 7X0,1 = 0,7W ... !!!

edit : typo correction ;)

alnath: I DID read your question, and wanted to point out the fact that a 7805 would probably need a heatsink, that's why I suggested DC/DC buck inverters ;) 7X0,1 = 0,7W ... !!!

Thanks for the warning and I do appreciate all information. 100mA was my peak usage on startup. Is idles at 40mW; 7x0,04 = 0,28W.On my breadboard it doesn't even feel warm to the touch, even when i up the input voltage to 15v.

Part of the problem is the project is a replacement dashboard clock and need to fit inside a certain frame. That's why i need feedback if the lm1117-adj i ordered is good. I wonder if there is a big difference between all the variants, or perhaps it is just marketing/branding.

The old clock is heavily outdated (1980's) and drains the car's main battery. This clock runs on the 12v when on, and uses a cell battery when ignition is off to keep the time (RTC chip).

Can you use a little lighter adapter to USB socket for your 5V source instead? I ran my Duemilanove for several days powered from one of these as a test. Actually got mine from the local hardware store, they had a whole basket of single output 1A adapters for $5, grabbed a couple. Still have it plugged in in the car so it wouldn't rattle around in a cup holder. http://www.amazon.com/s/ref=nb_sb_sabc?url=search-alias%3Daps&pageMinusResults=1&suo=1380637398342#/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=car%20usb%20adapter&sprefix=car+usb+ad%2Caps&rh=i%3Aaps%2Ck%3Acar%20usb%20adapter

CrossRoads: Can you use a little lighter adapter to USB socket for your 5V source instead?

Nope. My client (me) will not agree to such solution. Sorry if i'm stubborn.

You might consider a switching regulator. A lot less heat to worry about.

The MC34063 is what is known as a "jelly bean" part. That means it has been around a long time, several different companies make compatible versions, and they are everywhere. It is almost a certainty that any cigarette lighter adapter/charger you have, has this chip in it. There are several Javascript calculators around the web. The 555 timer is another example of a jelly bean part.

I like this one because you can enter a variation in percent of the input voltage, and it automatically selects buck or boost.

http://dics.voicecontrol.ro/tutorials/mc34063/

You'll still need to protect it from noise and voltage spikes with adequate filtering on the power going into the chip.

CrossRoads, the Dollar Tree here has those cigarette lighter plug to USB charger adapters for... a dollar. Great deal, you get MC34063, schottky diode, and a rewindable inductor.

Anyway, back to the OP's topic.

Ok so power cord, inline fuse, to MC34063 circuitry on the board, with some surge protectors/TVS or similar on the input side to help protect against high voltage transient spikes.