Electronic – Some Power Supply Questions – Multiple Rails or Single Rail w/ multiple Outputs

power supplyvoltage-regulator

I'm interested in making myself a 12V power supply. I need one because I often go out to places with little or no power and need some electricity to power my gear (which is basically a telescope, a camera and some accessories – all run on 12V).

I don't want it to be powered by mains and would instead use a 12V deep cycle battery. For regulation, I'm going to be using 7812. I need about 6 outputs, each capable of 4A. My question is this:

Is it better to regulate each output separately with a 7812 (with a power transistor for increased current capability) or use single 7812 with several power transistors, for a current rating of, say, 25A, and then split this into 6 outputs.

Secondly, since I'm using a 12V battery I understand that regulation is not going to be good as Vout is also 12V. Unfortunately, I can't get a new battery so I was thinking, perhaps, stepping the voltage with a DC-DC Converter to about 14V and then feeding this voltage into the regulator will help with regulation. Is this a good idea?

I require some decent regulation as my telescope is quite sensitive to the power's quality. I apologize if these are boneheaded questions, but searching the web did not return good results.

Best Answer

Forget the 7812. If you're going to use a switcher to create a higher voltage first and then use the 7812 to go to 12V, you might as well use the switcher to go to 12V directly.
If the output voltage is close to the input voltage (sometimes below, sometimes above), you want a buck-boost regulator, like National's LM5118. The Webench Designer creates a design to your parameters.