fixed tovariable power suply

[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: