24/48 power supply? will this work?

[imloggedin]

Will this power supply work? I just threw it together..

 

[owel]

Just use an 18-0-18VAC transformer (or higher), a couple of 317 regulators and you're done. Download the 317 datasheet for schematics.

 

[imloggedin]

I dont see how that would give me a 24/48 output? How do adjustable voltage regulators not change with the intput? If the output voltage of the transformer changes slightly.


And i do want the least amount of components

 

[imloggedin]

So does anyone see a reason this wouldnt wok?

 

[owel]

[quote author="imloggedin"]I dont see how that would give me a 24/48 output? [/quote]

Please don't tell this to my PSU kit customers. :roll:

How do adjustable voltage regulators not change with the intput? If the output voltage of the transformer changes slightly.

That's why they're called voltage regulators. They dissipate the extra input power as heat, and give you a constant output voltage.

And i do want the least amount of components

(2) regulators. One for the +24 and one for the +48.

As opposed to your (4) 12V regulators in your diagram. And you're using a 30-0-30 transformer too or is that a dual 0-30 transformer?

 

[imloggedin]

I didnt see a schematic for that power supply in the datasheet. What i was saying is.. isnt the adjust for the voltage regulator based on the output? so wont it vary with the input voltage? i dont know exactly how regulators work but thats just my random thought. By no means am i trying to dispute you, you know more about electronics than i do. just trying to understand.

 

[owel]

As I said, download the 317 datasheet.
Here's the link: http://www.national.com/ds.cgi/LM/LM117.pdf

You'll see there how it works and how to compute the resistor values for the output voltage you want.

 

[imloggedin]

ok i will do that. can you or anyone else comment on if the circuit i posted will work? thanks.

 

[Tekay]

http://www.vintagedesign.se/diy/Uni%20PSU.pdf
working fine with a single 24V AC transformer.

 

[jdbakker]

[quote author="imloggedin"]And i do want the least amount of components[/quote]
Why? It would help to know if you're motivated by space, cost or a strong aversion to soldering.

[quote author="imloggedin"]So does anyone see a reason this wouldnt wok?[/quote]
I see several, but it's hard to say which will dominate without having more context (most importantly the load connected to this supply).

What voltages do you really need? What currents? Any particular reason why you can't use a variation on one of the many PSU designs here or elsewhere (most notably SSLTech/Keith's)?

JDB.

 

[jdbakker]

[quote author="Tekay"] http://www.vintagedesign.se/diy/Uni%20PSU.pdf
working fine with a single 24V AC transformer.[/quote]
Be aware that that design needs a transformer with dual 24VAC windings, or one 24-0-24 winding, to get both positive and negative outputs.

JDB.

 

[imloggedin]

if you see several why dont u name some. it obviously has dual windings on the output.. look, 2 wires coming out of the middle. whats it take to get some answers here? im looking for simplicity, i dont want an adjustable regulator, so sue me. this circuit would be very easy to put on a board.

 

[PRR]

> Will this power supply work?

No, of course not.

Your "0V"s are tied together, so you would only have 24V.

BUT your 0Vs are tied together and two opposite polarity outputs are tied together... infinite current.

> I dont see how that would give me a 24/48 output?

Don't make owel personally draw you a picture... power supply plans are easy to find.

18VAC each side of the CT would make 25VDC each side. You may be able to use that directly. Or take owel's "or higher", like 24VAC each side to get 35VDC each side, and then regulate. (His commercial product probably under-loads an "18V" part, so it gives 20V-22VAC.)

You don't need 8 diodes and 4 main-caps to make 2 outputs.

> How do adjustable voltage regulators not change with the intput? If the output voltage of the transformer changes slightly.

The idea of a regulator is its output "doesn't" change with input. (Or "not much", "within limits".)

Maybe I am not understanding your angst.

 

[imloggedin]

My angst is because this could have been answered in your 1 post. Instead people must skirt around the subject offering their different solution instead of trying to teach someone.

Though i dont understand how my 0v's being tied together effects anything. Isnt the regulator just using it for a 0v reference? Like making 2 12v batteries and putting them in series? (Im trying to learn here)

 

[Tekay]

If you need +24v / +48v just skip the negative part then a single 24V AC will work just fine. We're using an almost identical PSU in all of our units.

 

[imloggedin]

how do i series them without the negative?

 

[imloggedin]

So i made this circuit in LTSpice.. heres the results...

So whats the problem? Is it wrong?

 

[imloggedin]

or put a resistor between the bottom leg and ground and you have 0-30-60.. or 0-24-48 if you regulate it, right?

 

[jdbakker]

[quote author="imloggedin"]So whats the problem?[/quote]
Spice doesn't mind simulating circuits that have ... issues when you try to implement them in the real world.

[quote author="imloggedin"]Is it wrong?[/quote]
What is the current flowing through the diodes? PRR already answered this, BTW.

JDB.

 

[imloggedin]

I didnt understand PRR's answer, and neither does LTSpice.

I dunno how much current is going through there.. maybe 200ma?