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im an student trying to make an home made power suply but im having trouble in the 5v 3A output could someone help me with and schematic using the lm323

Download the datasheet for specs and schema. Note: At 3A, you may need a heatsink to not trigger the internal shutdown from overheating.

you recomend me using an 7805 to provide the 5v to the lm323? if you want i can provide my scheme that i made( i know im asking dumb questions sry )

In page 4 of the datasheet (click on the link supplied in the previous post), near the top of the page, it is stated that you need an input voltage between 7.5V and 15V for an LM323.

If you really need 3A, you are still under the limit of 30W, that is (V_in - V_out) * current_through the LM323, but you may need a heatsink, dependent or the ambiant temperature (if inside an enclosure, it can be higher than the room temperature).

i think that solves the problem i was having 17v at the input il have to figure a way to lower it thanks a lot men :)

by any means does the 323-t differs from 323-a?(stupid question i know, im still learning)

The temperature range (at the junction means the internal temperature of the IC, approximatively) is the major difference (see page 1, right column, last paragraph) but also, the A version is better than the N version, having a narrower range of variations (ex.: output is 4.95 V to 5.05 V for the A instead of 4.8V to 5.2V for the N version, mentioned near the top of page 4, as example).

Generally, the marking follow the result of the internal testing procedures: if they need 1000 type A, let say, then they test for the strict specifications until they have the 1000 components and those which failed the strict specifications or those which are left untested, are declassified as type N. (The testing is costly, so they stop the stricter tests if they have no need for it. The IC must, statistically, meet the more permissive specifications tolerances though, but through less expensive testing procedures.) So, you "may" have quality of type A even with a type N, but you cannot rely on it unless you make the relevant tests yourself. Which is ok if you do one prototype, but not if you intend to automate a process which will make hundreds of the final gadgets.