LM2940 what capacitors?

Hello guys, I'm sort of lost. I read the data sheet for the LM2940 and understand I need two capacitors one on the input and one on the output. They need to be rated above my voltages also.

Now my confusion starts with ESR and capacitor type...

Would something like this work? https://www.sparkfun.com/products/8571

I have them around already. If not then what am I looking for exactly. Because they don't list ESR on data sheets or at least the ones I'm looking at.

Thanks for your time.

The datasheet for the LM2940 says that the output capacitor should be a minimum of 22µF to avoid instability.

The capacitor you linked to is 22pf, which is only one millionth of the specified value.

Sorry, that was my mistake. I was reading it on my break and was in a hurry.

You're a hobbyist so the ESR rating is not important and the voltage rating only needs to be 15% above the circuit voltage. Anything with that rating or higher is fine. As a general rule, the higher the voltage rating the larger the size so a 0.1 uF cap rated for 1000V is going to be much larger than one rated for 25V.

Thanks for the help, I'm trying to replace this in my circuit. http://www.mouser.com/Search/m_ProductDetail.aspx?Murata-Power-Solutions%2FOKI-78SR-5-15-W36-C%2F&qs=uJpRT2lXVNXJP%252bo08dQqJQ%3D%3D

Since it costs two times as much as a LM2940 and 2 capacitors. I was using the above to supply 5v to my Atmega328p-pu project in my automotive environment for controlling the signal that turns on some lights via Mosfet.

I just thought the OKI-78sr might be a little overkill in terms of cost for other similar stuff down the road.

So sounds like the LM2940 with proper caps would work just fine and save me over 2$ I'll probably add a diode to help with load dumping just for extra safety although I read a lot of people just use the basic circuit with great success.

I hope you know that the 2 are not properly the same parts, both are 5V regulators but the OKI is switching power supply, while the LM2940 is linear one, the main difference for your use is heat dissipated. Is your automotive environment 12V or 24V ? In second case the OKI is highly suggested.

Ciao, Ale.

ilguargua:
I hope you know that the 2 are not properly the same parts, both are 5V regulators but the OKI is switching power supply, while the LM2940 is linear one, the main difference for your use is heat dissipated. Is your automotive environment 12V or 24V ? In second case the OKI is highly suggested.

Ciao, Ale.

The environment is normal automotive so 12v but more likely over 12v I planned around 12 to 30v to be safe. Yeah I learned that the OKI was a switching regulator after the fact. At the time I bought them I needed a good regulator and was suggested the OKI.

Now that I have built it and it works I got rid of the arduino for a straight atmega328p-pu and wanted to see what else I can do to clean up the circuit to make it cheaper and better understand what I’m building.

The current requirement is super low as I am only powering the 328p at 8mhz internal clock and 2 mosfet that are used to ground the 12v source to turn on the LED’S.

I appreciate any input. I’m just trying to learn I want to use the most adequate parts not looking to over build just because, but I want to make the right choices since I might end up building stuff for other people later on and don’t want them to have stuff die because of crappie power regulations…

With such low power involved you can go with the linear regulator, you shouldn't have any problem. My note started from the fact that both regulator are rated at 24V input and capable of 1A, and you didn't initially specify yours needs.

Ciao, Ale.

ilguargua:
With such low power involved you can go with the linear regulator, you shouldn’t have any problem. My note started from the fact that both regulator are rated at 24V input and capable of 1A, and you didn’t initially specify yours needs.

Ciao, Ale.

Appreciate the help, yeah I don’t know the exact current draw I’ll try to look into that tonight but it has to be less than 100min I would think. That should be good for a lm2490 with no heat sink