HI EVERYONE
Great site and this is my first post.
I have a DC power supply 12 volts dc capable of giving of 2.5 A.
I like to convert this unit into variable voltage p.s. If I connect a pot at the output then is it acceptable. Thanks for the help.
Hi, Welcome to the forum..
No! not really.. If you use a pot then you will not achieve a constant voltage, what would work on one application would not work on another.
You need a vary the output via a power transistor.. If you don't need much current ie < 1 amp use can use a linear reg LM317 this can be used as a variable output.
If you look at the data sheet for the LM317 you will see how to hook it up. It also shows how to add a power transistor to increase the current output. But you will have to heatsink the LM317 and the transistor since, at worst-case, they will be dissipating 25W.
The disadvantage of the LM317 is that it requires about a 3V drop to operate so your maximum output voltage will be about 9V. If you want more voltage than that you can use a low dropout type regulator such as an LT1084 which can provide 5A with a dropout voltage of about a volt, giving a maximum output of about 11V.
Also note that the minimum output voltage of these devices is 1.2V, but that is not a problem for most applications.
Sorry about that I should have linked in the datasheet....As far as the LM317 is concerned, I have a similar setup but I have a switch the will give 12v straight out the supply in one position then the variable voltage in the other... I hardly ever require more than an amp for my circuits... The LT1084 will be a better choice as Carl suggested.
HI JimB
yes it is 2 the power supply is a fixed voltage regulated PSU with output of 12.5V, 2.5A. Really what I want to do is to have variable voltage from 0 to 12v.
So I am not sure yet if I can utilize LM317 at the output of mentioned power supply since the output voltage is regulated. Thanks a lot and still waiting for responses.
What's the general application? Replace adapters of radios or a true general purpose power supply. I have a really nice PS for that purpose. The secondary voltage is selected at the same time as the output voltage, so the dissipation is reduced. This **broken link removed** is a real nice supply for battery substitutiion.
HI JimB
yes it is 2 the power supply is a fixed voltage regulated PSU with output of 12.5V, 2.5A. Really what I want to do is to have variable voltage from 0 to 12v.
So I am not sure yet if I can utilize LM317 at the output of mentioned power supply since the output voltage is regulated. Thanks a lot and still waiting for responses.