9VDC AND 18VDC Together from an adapter???

[Kleber AG]

Thanks!!!  
Looks like the only difference between yors and mine is the caps right after the the 2 bridges? Can I use that caps like mines (both to the 0V gnd)

I may have it running today yet  :lol:

Kleber AG

[niftydog]

er yes... that's one of those boo boos I was talking about!

Treat them as separate supplies and you'll be ok.

[Kleber AG]

   
It works, perfect, thanks for all help!!!

9 "and" 18 VDC, fused, LED for power "on" and selectable for 110V or 220V AC.

It's a """1""" amper 12+12 transformer with 7809/7818 and 1N4007 for rectification.
So my question is what should be a best choice for FUSE value???

Thanks Niftydog and everyone!!!
Kleber AG

[niftydog]

lets say 9VDC and 18VDC, both at 1A; that's 27W.

Assume s*#thouse efficiency, maybe 70% or even worse...

40W input or there abouts

So, assuming you're using 110VAC?

That's less than 0.5A. I'd try a 0.5A.

Best way is to put your DMM in where the fuse should be, load up the circuit to the maximum you intend to use and read off the AC current flow. Then, go to the next highest rating of slow blow fuse that you can find.

Here's a tip; don't ever go to a shop and buy 1 fuse. Stupid.  :shock:  Buy a handful. Consider buying a range over and below what you think you need, so there's some flexibility.

[Kleber AG]

It's clean, stable, very cool...

Some questions yet:

1)Should I heat sink the regulators? Because it's not yet and it's already being used...

2)If I need to heat sink, may I use the enclosure walls for heat sinking it? It's a aluminiun box...

3)What is a diode some power-suplies uses across the regulator, I think reverse biased, what is it for? like this: http://www.generalguitargadgets.com/v2/diagrams/ultra_clean_ps_sc.gif

Thanks
Kleber AG

[RobB]

The aluminium enclosure should be a good place to sink heat.  It would be a good idea to use isolating washers in case contact with the enclosure introduces an earth loop.  The centre pin on the 78XX series of regulators is connected to the metal part of the transistor case.  

The diode from output to input is there to ensure the output voltage never exceeds the input voltage.  This could happen when you turn your supply off.  If the output exceeds the input by too much the regulator could be damaged

I’ve been thinking about making a regulator box running off three DC unregulated plug packs.  It would produce outputs of +15, +9 and â€"9 (including +&-9) for all my stomp boxes.  The only reason I haven’t yet is because I’m worried about earth loops creating hum.  Still thinking about it.

[Kleber AG]

:shock:

The diode from output to input is there to ensure the output voltage never exceeds the input voltage. This could happen when you turn your supply off. If the output exceeds the input by too much the regulator could be damaged

I've used big caps on mine (1000uF) and after I turn it off, it stays "on" for so longgggg...
I believe I do not have more room for anymore components, I can't put that diode there    Would it really happen to damage my 7809/7818

About the heat sink, I may try to sink to box walls, but I have no whashers(will washers reduce the sink ability?) I have my box ground to the third pin of the power wire, altough I always run it to two pins outlets, I'm afraid of ground loops  :?

I've used a too small enclosure... I always do, and later the project finish having no option to mods/updates/improvements...

Thanks
Kleber AG

[Gilles C]

Here is how we would get 2 voltages from 1 XMTR and 1 rectifier bridge in the old days of ham radio...

The whole circuit:

http://www.finitesite.com/gtechblues/My_images/PowerSupply1.gif

What is used (half bridge) in the lower voltage part of the circuit:

http://www.finitesite.com/gtechblues/My_images/PowerSupply2.gif

Please note that the current of both supplies go through the lower diodes.

This kind of circuit is good when the lower voltage won't have to output as much current as the upper (higher voltage) one because it is only a half-wave rectifier.

For you info only. You don't have to use...  

[Kleber AG]

The diode from output to input is there to ensure the output voltage never exceeds the input voltage. This could happen when you turn your supply off. If the output exceeds the input by too much the regulator could be damaged

Why there's nothing (I think) at the datasheet about this diode protection???

And in wich case would the regulator be damaged? Not always that it's turned off?
uhmmmm...

I must learn to left room at my projects for future changes  :x looks like I will "must" insert 2 diodes (one for each regulator)

Does anyone have anymore info about this subject???

Regards
Kleber AG

[zener]

I hope you don't mind if I jump in because I'm doing the same thing.

I have a center tapped 12V transformer and I want to have 24v and 12v. How do I know what's the +12v and the -12v, probab;y with a DMM. There's no label in it?

[Kleber AG]

I'm gonna gig today, without that diode protection :roll:
If someone could advert me if it's really a must have diode...

Thanks
Kleber AG

[puretube]

check this thread, too :
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=23268

[niftydog]

Should I heat sink the regulators?

You should; Especially if you're planning on actually drawing close to 1A as you originally mentioned. Be sure the electrically isolate them from the chassis, as the 78XX tab is GROUND, whereas the 79XX series tab is INPUT! (Nothing to do with ground loops!) And yes, the washers will reduce the heat transfer. The only other option is to have two separate heat sinks.

What is a diode some power-suplies uses across the regulator

Forget the diode, it is certainly not essential. You probably won't have a problem. Besides, the output voltage is dependant on the input voltage. And with such big caps on the input, it's unlikely that the regulator will ever be reverse biased.

I have a center tapped 12V transformer and I want to have 24v and 12v. How do I know what's the +12v and the -12v, probably with a DMM. There's no label in it?

It's AC, there IS no + or - side. They're both the same. The + and - bit comes in when you rectify the AC into DC.

[Paul Perry (Frostwave)]

To really prote4ct a 3 terminal regulator, you need to make sure that first, the input is never the wrong polarity, and second, the output is never connected to a voltage higher than the input.
Which requires TWO diodes, as shown here:
http://www.nzart.org.nz/nzart/examinat/amateur%20radio%20study%20guide/Course%20Files/Power%20Supplies%20-%20Regulated/STUDY%20NOTES%20-%20REGULATED%20POWER%20SUPPLIES.htm

[Kleber AG]

Thanks
I'm back from the gig,

I used the power suply(I had a backup just in case) and it worked during all the gig, I've heat-sinked it to the walls of the aluminiun box.

Be sure the electrically isolate them from the chassis,

Its not isolated, instead it's pretty electrically connected to the chassis.  :roll:

It worked nice, without ground loops, pretty good. But man, all the enclosure get super-hot and it was in a really cold night...(and I had drilled holes all over the enclosure)
Is that normal? ??
Also niftdog do you think I must isolate the regulators from the boxes???

Its a really nice thing to have, your own DIY power suply, the way you need it, THANKS SO MUCH  
Kleber AG

[niftydog]

Is that normal?  ??

Yes, if you're pulling lots of current. Like I said before, 1A is the MAXIMUM you can draw from these regulators, PROVIDING they are adequately heatsinked!

do you think I must isolate the regulators from the boxes???

absolutely yes!

Did you use both the + AND - at the same time during your gig? if so, frankly I'm amazed that it worked!

From memory the 78XX tab is ground, where as the 79XX tab is input. If these are connected together, you effectively ground the input of the negative power supply. Result = no negative supply and a very unhappy rectifier!!

[RobB]

Did you use both the + AND - at the same time during your gig? if so, frankly I'm amazed that it worked!

Niftydog, Kleber was only using positive supplies.  Both regulators are if the 78xx series.  It was me who suggested building a PSU with both +ve and - ve outputs.  

As far as the diode from output to input is concerned, I have in the past used these regulators without it and never had a failure but it is common practice to include this component.  Today, at work I noticed a 78xx regulator on a pcb which was part of a PA system.  The diode was there.  

Kleber, I’m glad your PSU doesn’t cause hum.  Thanks for doing the experiment.  Based on your success, I’ll go ahead and build mine soon.

[Paul Perry (Frostwave)]

One good thing about 3 terminal regulators is that they (often) have a thermal cutout. Which should make them immortal. But..... :oops:
I have found that National and Motorola are more robust than some of the 'off-brand' cheapies, at least in my rough hands.

[Kleber AG]

Thanks guys, you're so cool
I guess I should measure how much current I'm pulling with this "coffee burner"
And then may it be a good idea to still install a real Heat-Sink piece, just fixed at the enclosure oposite side out from the regulators? I mean there's 2 regulators together, but I'd just use one big Heat-Sink for both and outside the enclosure just fixed "at" "the" enclosure.

Niftydog, Kleber was only using positive supplies. Both regulators are if the 78xx series.

Yep Rob is right...

""do you think I must isolate the regulators from the boxes???""
absolutely yes!

Sorry I'd like to understand "why"? Because it had no HUM at "that" gig, may it HUM somewhere else? At different situations?
This Power suply I built with a 3 prong power cable, the one like computers, and the security "third" pin I connected to the enclosure, does it made any difference???

OK, I'm gonna keep it "without" that diode protection.
I want it to be safe and reliable because I'm gonna travel to Europe for "many" gigs there (2 months) and I need my rig working perfect.

Thanks for your precious help mates!!!
Kleber AG
PS: Hey Paul I found that thermal cutout point in home before I heat-sinked it, I tried to run all my pedals and all of them started to "led blink" after a while :lol:  That was funny, glad I was still at home...

[niftydog]

Niftydog, Kleber was only using positive supplies

DOH! Sorry Kleber.... you don't have to isolate the regulators at all!

Thanks Rob!

As for the hum thing; hard to say really. But you get hum when you have a ground loop that involves the signal ground. Having two regulators very close to each other with their grounds connected is probably a low risk for ground loops.

Still, you'll probably find that most of the hum you get in a guitar system is due to the venues lighting system interfering with your pickups!