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Old 30th December 2009, 03:51 PM   #1
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Default 12-14.4v to regulated 12v & 5v

Ok this is going to sound like i'm contradicting my self but i want a low noise power supply to provide 12v and 5v clean output, from my car (so 12v when engine off, 14.4 when on).

I'll need maybe 30watts available (25w max for a DVD drive and the rest is only to power a spdif convertor (maybe ~100ma? ~2watts?)).

I have no idea how much more a dvd drive robs at 5v than 12v or vice versa. I assume it's like 20w-12v(motors) and 5w-5v(guts).

Just for starters give me 25w @12v and 25w @5v.
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Old 30th December 2009, 04:02 PM   #2
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5v is sorted!
http://www.national.com/images/pf/LM2596/01258301.pdf

Just need a regulated 12v now.
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Old 30th December 2009, 08:27 PM   #3
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Look up a topology called sepic.. this will provide you with the ability to both step up and down from the input voltage. You can get 12V from the battery when the car is not running and while the generator is running and providing providing ~14V on the battery you will still have 12V out.

EDIT: National guide here: http://www.national.com/an/AN/AN-1484.pdf

\\\Jens
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Old 30th December 2009, 09:03 PM   #4
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I would be interested in seeing your implentation of the DVD, or even plans to do so. Maybe a post in the car audio forum?
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Old 30th December 2009, 09:31 PM   #5
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Why the 12vdc when the engine is off and 14.4 when on. If it will run off 14.4v
why build a 12v supply? If you must have 12v your fully charged car battery with
the engine off will be about 12.6v are you sure it won't work on 12.6v instead of
12v?
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Old 30th December 2009, 09:41 PM   #6
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Quote:
Originally Posted by tsmith1315 View Post
I would be interested in seeing your implentation of the DVD, or even plans to do so. Maybe a post in the car audio forum?
I will do. Hopefully DVD out via spdif, into a spdif converter, then into (hopefully) a Denon DCT-A100.

Quote:
Originally Posted by woody View Post
Why the 12vdc when the engine is off and 14.4 when on. If it will run off 14.4v
why build a 12v supply? If you must have 12v your fully charged car battery with
the engine off will be about 12.6v are you sure it won't work on 12.6v instead of
12v?
Erm, i doubt it will work of 12.6v tbh, I thought PC components are very sensitive to voltages...
14.4v when engine running as alternator charging voltage?
Yes more like 12.6-12.8v, but the point is still the same ( don't forget on load voltage (the rest of the system runnign will pull this down to closer to 12v too ).

Quote:
Originally Posted by JensRasmussen View Post
Look up a topology called sepic.. this will provide you with the ability to both step up and down from the input voltage. You can get 12V from the battery when the car is not running and while the generator is running and providing providing ~14V on the battery you will still have 12V out.

EDIT: National guide here: http://www.national.com/an/AN/AN-1484.pdf

\\\Jens
I will have a look at that, thanks. It's just the difficulty of sorting out inductors.... Never messed with them before .

........

How about something like this???

12v Regulator Schematic (15A) - MP3Car.com
Post #7 is the updated schematic. But not 1Kohm I think, across the gate and collector, it says something about 220ohm later on.
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Old 30th December 2009, 11:27 PM   #7
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Quote:
Originally Posted by woody View Post
Why the 12vdc when the engine is off and 14.4 when on. If it will run off 14.4v
why build a 12v supply? If you must have 12v your fully charged car battery with
the engine off will be about 12.6v are you sure it won't work on 12.6v instead of
12v?
After re-reading this, it was all a little confusing I need 12v not, 14.4.
So i was just emphasizing the application of it being in car. I need 12v from unregulated 12-14.4v.
Sorry about that
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Old 30th December 2009, 11:59 PM   #8
gootee is offline gootee  United States
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Quote:
Originally Posted by agithegreat View Post
After re-reading this, it was all a little confusing I need 12v not, 14.4.
So i was just emphasizing the application of it being in car. I need 12v from unregulated 12-14.4v.
Sorry about that
Jens is probably always correct. ;-)

Download LT-Spice from Linear Technology - Linear Home Page (free). When it starts, select File then 'Switch Selector Guide' (at least that's what it was called in my rather-old version). You will be allowed to enter your min and max input voltages, your desired output voltage and max current, and you're halfway there. It will probably suggest only SEPIC converters, and will design them for you. National Instruments has an on-line power supply design tool that is pretty cool, too. http://www.national.com .

If you've never done an automotive circuit, before, then, be afraid, be very afraid. Just kidding (somewhat). But you do need to worry about various types of transients. You would probably want to Google something like "automotive electrical OR electronic transient". You could want to think about using devices to absorb or divert large (say 100V) "load dump" voltage spikes that might last 0.5 second (maybe avalanche diodes, or 'transorbs', or something, or even a special IC). And jump-starting and cold-cranking both cause other phenomena.

Cheers,

Tom
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Old 31st December 2009, 02:05 AM   #9
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Quote:
Originally Posted by gootee View Post
Jens is probably always correct. ;-)

Download LT-Spice from Linear Technology - Linear Home Page (free). When it starts, select File then 'Switch Selector Guide' (at least that's what it was called in my rather-old version). You will be allowed to enter your min and max input voltages, your desired output voltage and max current, and you're halfway there. It will probably suggest only SEPIC converters, and will design them for you. National Instruments has an on-line power supply design tool that is pretty cool, too. http://www.national.com .

If you've never done an automotive circuit, before, then, be afraid, be very afraid. Just kidding (somewhat). But you do need to worry about various types of transients. You would probably want to Google something like "automotive electrical OR electronic transient". You could want to think about using devices to absorb or divert large (say 100V) "load dump" voltage spikes that might last 0.5 second (maybe avalanche diodes, or 'transorbs', or something, or even a special IC). And jump-starting and cold-cranking both cause other phenomena.

Cheers,

Tom
Thanks

I forgot to say that all this will be powered off a relay which will only be on when my headunit is on (via remote output). So never on for engine starts, or any funny business, so i'm hoping that would make me immune to voltage spiking etc??
Or should I still take this into account.
The relay will be before the input to the regulator, so basically what I let my amplifiers, on load, see i'll let the regulator see.

It's a steep learning curve, fetching the basics, but it's fun.

Thanks for your help so far.

I'm playing with said software now, but how do I go about winding inductors, or what's the deal with them?
Sepic was mentioned above but I disliked the idea of using inductors, as I have absolute zero experience with them.
Can't find anything allowing me to design a regulator? It's all just pure drawing software...
If you can, could you please send me through your version?
alex_hemming (at) hotmail.com

Last edited by agithegreat; 31st December 2009 at 02:26 AM.
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Old 31st December 2009, 03:32 AM   #10
gootee is offline gootee  United States
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I don't think that I have the archived version of mine, any more.

What are the sub-menu options in the main "File" menu option?

Also try national.com's Webench power designer. It's on line, with nothing to download.

Last edited by gootee; 31st December 2009 at 03:35 AM.
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