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fixed tovariable power suply - Click HERE for Original Thread
salil_kamat2
I am a first year ELECTRONICS postgraduate student from Mumbai,INDIA. I want to know whether we can convert--dual power supply i.e. the one built using LM7805(positive voltage regulator) and LM7905(negative voltage regulator) to make a variable supply which uses LM317 (adjustable voltage regulator) ????

Basically, can we find such a circuit which establishes a relation between the two?

Hope that you will definitely help me out at your very earliest!

PLEASE HELP ME !!!!!!!!!!!!!!!!!!!
richie00boy
You can use the transformer and rectifier, caps etc. The max output from the unit will probably be about the same as with the fixed regulators though. Also a new board will need to be made as the pinouts are different.
paulb
The 7905 would be replaced by an LM337 (adjustable negative regulator).
jackinnj
if you want to establish the relationship between the two, go onto National Semi's website and search under "tracking regulator" -- it's a bit more complicated than just plugging in an LM337 for an LM3905 -- but you can control the output voltage with only one potentiometer thusly:

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