Jump to content

Voltage regulator 12vdc to 3.3vdc

Recommended Posts

What are y'all using for a voltage regulator from 12vdc to 3.3vdc. It is going to be an automotive feed so I'm looking for something with a 25 volt ceiling at least to handle the noise from the alternator. Through hole for now...




Something like this has crossed my mind but am wondering how much heat I'm dumping off of it.



Link to post
Share on other sites

I typically use these for such applications-




Switching type regulator, so much less heat.  Rated up to 36V, designed for nominal 12V or 24V applications (Vin(MIN) = 7V fyi)


Fwiw- I have one of the 5V versions of this in my wife's car running an arduino-based project that has been running continuously for some 2.5 years now... it works great.

I did end up putting a filter cap and fuse in-line before the regulator after doing some research into alternator load dumps and the high voltages possible with alternators & noise and such.  Can't recall the exact values for all of them, but one piece involved a 1uF high voltage rated film cap.  Should be high voltage rated anyhow (150-250V or so to cover the worst case scenario).  Then a TVS diode and fuse to blow in case you get such a massive dump.

Link to post
Share on other sites

Well, a lot of options, depending on application...


What current? Is it relatively constant? Do you need 1/2amp?


If the draw is below 25mA to 50mA average (over a time <1sec), the basic linear reg is a good choice here, as it is cheap and regulates well. At 50mA, you will be dumping about 500 to 600mW, which is into the range where you need to worry about rejecting the heat with a heatsink. Greater than 50mA, definitely a heatsink and other choices are likely better.


Constant current (or fairly constant) up to the limit for the unit allows for the use of a series ballast power resistor to drop voltage and dissipate heat


My choice would be a switching regulator rated for automotive conditions (buck configuration) to 3v3, OR a switching reg to 4.5V, followed by a 3v3 low drop out regulator, if I need silky clean output. I might even just modify a $5 phone charger to deliver the 3v3, if I had one around, as even the cheapies use a buck configuration switcher (caveat: there are some that go beyond cheap to the level of trash.... they are often scary)

Link to post
Share on other sites

At those currents, if you have the linear reg in hand, and can mount the heatsink, it will do the job. I have done such many times (back in the 70's and 80's, linear regs like the 7805 or LM317 were all we had off the shelf), and it works.


But, as Spiralis said and I followed, the switcher reg is the better choice. The OKI-78SR he referred to is about as good as they get for off the shelf price/properties balance for this type of application. Never used that one myself, as I have a collection of switching drivers and inductors from an assortment of past projects, most of which were paid for by others, and just roll my own when I need to.


Another option I didn't mention is, for low duty cycle applications, like 100uA 99% of the time, 100mA or an amp 1%, is use rechargeable cells and a low current maintenance charger. I have used NiMH (previously NiCd's) and AGM's a number of times this way. 1A 2% of the time and microamps the rest requires about 25 or 30mA from the charger to maintain the battery. Drawback is battery life issues, but, especially for things that need to stay alive for a bit with no power at all, this works well.


In an auto application, I would also suggest a good filter at the input. There are commercially available filters for noisy sound systems which are usually just an L-C. (See second in attachment)


If using a filter, I would suggest a zener or other protection device at the output side to clamp any major spikes to 20V or so.


edit: put linear rather than switcher... need sleep


Link to post
Share on other sites

You can get LM2596 (or high voltage version LM2596HV) based DC-DC converters from eBay for as little as $1.


I've seen those regulator modules on eBay as well.


I cannot understand how they can offer those fully assembled units so cheaply. The parts alone are more expensive than the final cost!

Link to post
Share on other sites

Imports from China (assuming this is where they are from) are known to use "knock-off" components. These typically don't meet the spec sheet of the original. This reduces cost but the old adage, "you get what you pay for" applies.

If I were to install one of these I would likely fuse the daylights out of it. :)

Link to post
Share on other sites

A recent article at hackaday on the nRF24L01+ modules coming from China shed a lot of light on that topic. Different silicon node size, likely reduced sensitivity/etc are behind those, in fact the true name of those chips (SI24R1) is revealed which is well known... and has an extra +7dBm TX mode not present in the genuine Nordic silicon, likely to help overcome the sensitivity shortcomings of the knockoff. You do get what you pay for.


Sent from my Galaxy Note II with Tapatalk 4

Link to post
Share on other sites

I did get a few of them, but there going to just be temporary only.  I am waiting for the new Cree CXB3590 to show up at Mouser then I will order regulator parts along with all the other odds and ends on the list. 


Biggest think I am worried about getting power off the vehicles is the crap noise and voltage spikes.  I am going to build mine with all 50v components.  I would have thought modern vehicles would not have this problem. 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...