Simple 12V power supply build

[.Mike]

I'm not sure if the circuit is going to require any real current.. it'll be be a bunch of stuff thrown together. What would be a real current? The only thing the 5v will be feeding is 4 pt2399 chips and I can't find a current draw for them in the datasheet.. I may be missing it though

PT2399: http://www.datasheetcatalog.org/datasheet/PrincetonTechnologyCorporation/mXyzsyzt.pdf

There are several PT2399 datasheets floating around. The 16 page version (1.4) is the most thorough: http://www.tubes.it/PT2399.pdf

The supply current is 30-40mA. So let's say 40mA each, or 160mA total. If I've got this right, you take the 12v output from your 7812 minus 5v after your 7805 = 7v to burn off. 7v multiplied by 0.16 amps = 1.12 watts of heat dissipation minimum from the 7805.

I don't know if that requires a heatsink, though, sorry...

Mike

[mth5044]

You want 100n caps to ground on either side of all the regulators to help quieten them down and you can also use an opamp for the 6V supply to get a low impedance output or use a 5V regulator with resistors to lift it to 6V. Maybe even make your first 220uf 2 x 100uf with a 100 ohm resitor between them as a low pass to get rid of a little ripple.

Alright, I added a 100n cap between the 220uF and pin 1 of the 12v regulator and one right after it before the 100uF cap. I thought that one would be considered as both before the 5v and after the 12v  Then there is one after the 5v regulator already. I'm not too sure what you mean about the 100ohm resistor though? Do you think it is something really necessary, or just extra caution?

There are several PT2399 datasheets floating around. The 16 page version (1.4) is the most thorough: http://www.tubes.it/PT2399.pdf

The supply current is 30-40mA. So let's say 40mA each, or 160mA total. If I've got this right, you take the 12v output from your 7812 minus 5v after your 7805 = 7v to burn off. 7v multiplied by 0.16 amps = 1.12 watts of heat dissipation minimum from the 7805.

I don't know if that requires a heatsink, though, sorry...

Mike

Whaaat I didn't know that there was an extended data sheet! That is awesome. I don't know if that means I need a heat sink either, but thanks for doing the math!

And a fuse on the mains couldnt hurt anything...

I don't know the first thing about picking out the right fuse, so any idea what ratings I should look for? I think it goes between the AC cord and pin 1 of the transformer, right?


Thanks everyone 

[petemoore]

  current tends to vary and can be controlled, volume control, bass control etc.
  Starting with more Ma than you need or with low volume, testing chip temperature as volume/current is increased [quick touch, fairly quick touch [sometimes that second one'll getcha, leave a burn mark..].

[G. Hoffman]

Personally, I'd put a heat sink on AT LEAST the 5 volt, and as you are using a bridge rectifier, I'd want one on the 12V rectifier as well (you get more voltage out of a bridge than a full wave).  But I am far from being an expert in this, I just like to over engineer whenever possible.


Gabriel