how to build a 5v 1.5 A power supply?

hi all..am in need of building a 5v 1.5 A power supply for powering my board..previously i built a power supply but the current output is not good enough to power the board..can u tell me which series of 7805 is reqd to get 1.5A??also tell me the design eqns of computing the capacitor values..and is it possible to get 5v 1.5 A output from a transformer of 12v 500mA?

pls suggest me a solution..thank you..

Hi,
12v 500mA is 12*0.5 = 6W. 5v*1.5A = 7.5W. So it's not possible.
If you use 7805, you can't draw more than 400-500mA from your transformer. If you used switching, you could draw about an amp or so.
For 1.5A, you can't use 7805. You can use LM317 or LM350. If you use switching, take a look at L4971.

Generally, we can use 1000uF per amp of current. So 1500uF would do. You could use higher for lower ripple, eg, 2200uF.
The voltage rating has to be atleast 2xAC voltage. So if you have 12v AC coming in, the capacitor must be rated at more than 2x12 = 24v. So a 25-50V would do nicely.

Example regulator circuit:


Hope this helps.
Tahmid.

---------- Post added at 18:52 ---------- Previous post was at 18:51 ----------

For R2, you could have a pot so that you can adjust the output to perfect 5v to compensate for resistance tolerance.

78S05CV from ST will supply up to 2 Amps if adequately heatsinked.

place two 7805 in parallel

Drawing more than 200mA will generate heat in 7805. You should have a good heat sink

The use of single 7805K (TO3 Package) may be considered in place of TO220 for upto 3 A regulated output.
Cheers

U should use lm317 in place of 7805