Jump to content
43oh

Best Way to go from 12V to 3.3V to power an MSP430G2231?


Recommended Posts

Yeah, that's why DC-DC converter should be considered if higher current is required.

 

I'm using around 2A in this particular design. Even just idling though it seems to heat up the LM317 pretty good. I haven't noticed the 12V to USB plugs/chargers getting this hot.

 

Maybe they use a DC-DC converter in those things.

Link to post
Share on other sites

I wonder if it'll work with a heat sink.

 

EDIT: come to think of it, I only have just the MSP430 running on the regulator. All other circuitry I have unregulated since it's operating voltage parameters are much higher than what the V+ supply is. So there is not 1.5A going through the regulator.

 

But it's still getting pretty hot.

Link to post
Share on other sites

You're regulating 12 volts down to 3 volts. Thats 9 volts difference. Let's assume you draw 20mA (I don't know exactly how much power a Launchpad draws, or all the logic you need to power from 3 volts). This means you need to convert 180mW to heat (9V*0.02A). The LM2937 in TO220 case has, according to the datasheet, a thermal resistance of 53K/W (page 8), meaning its temperature will rise about 10 degrees (celsius) above ambient. If you draw 40mA, it will rise 20 degrees. 100mA would mean nearly 50 degrees above ambient, enougt to burn your fingers. (The TO-263 and SOT223 cases have an even higher thermal resistance, meaning the will get even hotter with the same load)

Link to post
Share on other sites

USB chargers convert 12V to 5V and can supply at least 500mA. They must be using switching regulators, otherwise the heat would be excessive. They have the necessary protection circuits. And they cost about $5...

 

I would really recommend getting one and then either try to change the output to 3.3V like cde suggested, or just use your LM317 to go the last step to 3.3V. I would suggest the latter, because it gives you a nice and smooth supply, something a cheap china-made charger might not provide.

Link to post
Share on other sites

If you're going from 12v to 3.3v, even a low amperage quickly adds up to a lot of heat to dissapate. :?

Didn't he say 'vehicle' ? That goes up to 14.4 if the regulator is working, if not it gets much worse. That's 11 Volts to waste. I would go in three stages, down to 9V, 5V and then 3V3. Or simply put 15-20 diodes in series.

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.

Guest
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...