12 volt supply help

[moneypit]

hi guys, i got recruited helping one of my friends out with a pedal board for guitar effects (5 or 6 stompboxes) all 9 volt. i know any of the non regulated supplies range from 9.5 to 14 volts so i figured i'd go with 12 volt. anybody see a problem with that? question number 2) originally i was going to do a 9 volt supply so i bought a 12.6 volt transformer (6.3-0-6.3) am i going to run across a problem with the 12volt regulator (lm7812) not having enough of a voltage differance (i'm using a 3300uf cap) so there's a little extra voltage from the cap unloaded. any suggestions, thanks.................frank

 

[Kamel]

seems to be too just, check the math but with ten percent of loaded loss plus the two diode voltage drop of the rectifier, you will be under the 3v volt between input and output of the regulator, try to put a nine volt reg (don't know if it exist) or a 6 volt reg with a 3 or 4 volt zener on the ground leg of the reg

 

[pstamler]

I'd think about using an adjustable regulator such as an LM317.

What current will you be drawing from the supply, and what's the current rating of the transformer?

Peace,
PAul

 

[mad.ax]

Question 1: Some pedals demands a regulated 9VDC psu. Perfs, sound, and reliability are only guaranted at 9V, not at 12!

Question 2: Stick with your original plan. Use an LM317 as Paul adviced, or if you wanna keep it ultra simple, change your LM7812 for a 7809...

I.E. you can get this one (1A, TO220) for 0.44$ at mouser:
http://www.mouser.com/Search/ProductDetail.aspx?qs=iPumNTI%2f3jWvVyiHbYXbVg%3d%3d

Axel

 

[Sleeper]

One thing though I'd have to disagree with Kamel. if you've got 12volot transformer and you hang a bridge rectifier on it you should have no problem meeting the input output differential for the vRegs. The voltage on the other side of the bridge is usually a few volts higher than what is stated on the transformer. every time- in my expereince. and that just confirms in practice the theory that I'd already read a bunch of times from the likes of PRR SSLtech New York Dave and BCarso and I've missed a few names, but if these guys say something will work it does.
Kelly

 

[moneypit]

hey guys, it looks like it'll be drawing about350 ma. full wave bridge so i'm seeing about 17 volts at the cap (3300uf) and then i got another 10uf from output to ground so far, it looks pretty stable (11 volts out)with load

 

[moneypit]

hey guys, it looks like it'll be drawing about350 ma. full wave bridge so i'm seeing about 17 volts at the cap (3300uf) and then i got another 10uf from output to ground so far, it looks pretty stable (11 volts out)with load

 

[moneypit]

hey guys, it looks like it'll be drawing about350 ma. full wave bridge so i'm seeing about 17 volts at the cap (3300uf) and then i got another 10uf from output to ground so far, it looks pretty stable (11 volts out)with load

 

[mad.ax]

Usually, TO220 78XX are speced 1A, so a 350mA load should not be a problem...
But 11 Volts at the output of a 7812 looks wrong! You should get 12V.
So you have a problem with either your meter or with your ckt...

Axel

 

[pstamler]

You don't say what the transformer's current rating is. If I assume it's 0.5A (500mA), then you can do a 2-stage filter (with 3,300µF caps and a 3.9 ohm 2W resistor) and an LM317 regulator (Rout-adj 200 ohms, Radj-ground 1240 ohms bypassed with 100µF cap), and you should be fine for 9V out. Maximum regulator dissipation will be about 2.5W, so heatsink accordingly.

Peace,
Paul