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12 volt atx power supply circuit

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letherby

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hiya all

would like to run a computer mother mother board in my car.. been down the root of using a inverter but takes a lot current evern in when the computer is not on would like to make a 12 atx power supply.. so any help .. know little bit of eletronics,, been into it for years now but not gone into switch mode power supply yet any help?

thanks all
 
to build an ATX supply you would need to make +12v, +5v, +3.3v, -5v, and -12v power rails, not to mention add more circuitry for the ATX-specific I/O (power good, power on, etc) the 12v rail essentially needs to be a buck-boost stage, which makes it more difficult... and on top of all, the 12v and 5v lines in particular need to be able to handle a lot of power. Plus, switching DC-DC converters are not exactly trivial design.

That's not to say it's not doable, you can search the mp3car forums for a design for a homemade supply (search for mastero/sproggy). It's composed almost entirely of MAXIM brand switching controllers that have built in switching transistors, which are quite expensive (power transistors are large but normally cheap because making them requires only a few layers during manufacture, but by putting control circuitry on the same device they have to use a lot more layers, so it is both large and complex, ie - $$$), unless of course you get them all as free samples.

However, by the time you get done building one I would expect you would have spent more money than simply buying one of the application-specific DC-DC ATX supplies such as those sold at the MP3car.com store... they have a 160W supply for $90.

However, there is a MUCH MUCH simpler solution for you if you don't want to spend the money building or buying a power supply... you need to do what most people running carPC's on inverters do, which is to simply TURN OFF the inverter when the computer is not running, by either cutting power to it with a large relay, or disconnecting the power switch with a smaller relay. All it takes is a simple microcontroller (or even a sequential logic circuit if you prefer that sort of thing) and you can have a circuit that turns on the inverter and boots up the computer when the car is turned on, and then powers off the computer and turns off the inverter when the car is turned off. This sort of device is commonly referred to as a shutdown controller, plenty of info on the mp3car forums, you can go from something as simple as relay logic to as complex as a microcontroller board with advanced timers, temperature monitoring, etc. I have designed and built one that is mid-range as far as complexity, you can find it on my website in my signature.

Not that I don't think that a DC-DC is a good idea (much more efficient and much less electrically noisy), but I think that trying to build one just to fix your power draw when the computer is off is like buying a new car just because you have a leaky tire, when you could instead fix the problem simply and cheaply.
 
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