Transformer problem

[schmitt trigger]

"the input needs to be at least 26V."
Actually somewhat higher because of the valley in the ripple voltage.

 

[Hero999]

"the input needs to be at least 26V."
Actually somewhat higher because of the valley in the ripple voltage.

Yes, you're right, I should've said, the minimum ripple valley needs to be 26V.

 

[xXAxHillbillyXx]

Just a little footnote but whatever is built it should be built around existing mains power. A transformer for 220 V mains would not fare to well here in the US. This works better when people include their locations in post. I guess we can assume the poster has 220 Volt mains power?

Ron

Yes I live in the United States

The LM317 will nearly do that.

The maximum current rating is 1.5A but I've had no problems drawing 2A for extended periods of time. the datasheet says the the current limit varies between 1.5A and 3.4A, 2.2A is typical but don't bet on it. The current can also be boosted by adding another transistor or more.

The current limit is fixed between 1.5A and 2.2A but can be made adjustable by adding a couple transistors.

The minimum voltage setting is 1.25V but it can be reduced to zero using a band gap reference or an op-amp.

https://www.electro-tech-online.com/custompdfs/2010/03/LM117-1.pdf

It depends on what you want.

How important is:

Operating down to 0V?
Having an adjustable current limit?
Being able to supply 2A rather than 1.5A?

As previously mentioned, it's possible to do all of the above, with additional components.

Operating down to 0V is not important but I would like it to be close to it like 1.5V
I do want adjustable current limiting
1.5A is fine it does not have to be 2A
And it does not have to go all the way to 20V but I would like at least 12V

 

[Hero999]

Yes I live in the United States

Operating down to 0V is not important but I would like it to be close to it like 1.5V
I do want adjustable current limiting
1.5A is fine it does not have to be 2A
And it does not have to go all the way to 20V but I would like at least 12V

That makes things much easier.

Connect the following two circuits together:

**broken link removed**
Change the following values:

R1 = 120R
R2 = 2k

Mount the LM317 on a large heatshink, such as one from an old pentium 3.

**broken link removed**

C = 4700µF, 50V
D1 to D4 = 1N4001 or a 2A bridge rectifier module.

Replace the load with the previous circuit, + to - and the earth/ground symbol to -.

Replace the sinewave generator (left of the bridge rectifier) with a 50VA (or greater) 120V to 24VAC mains transformer.

EDIT:
You should include a mains fuse in series with the transformer's primary, 500mA slow blow or 1A will do.

If you put the circuit in a metal box you must connect the metal to the earth/ground conductor. All mains connections should be covered with a layer of heatshrink.

 

[xXAxHillbillyXx]

I do not see the earth ground symbol in the second schematic, and i also do not see a pot for adjusting current, am i just missing it?

 

[Hero999]

There isn't one.

My previous post contained a typo which I've corrected.

Connect the earth/ground symbol to to the negative of the second circuit.

Note that the earth/ground symbol does not need to be connected to earth/ground, it's just the 0V reference.

You said you didn't need to adjust the current, so there isn't anything to adjust the current.

I do want adjustable current limiting

 

[xXAxHillbillyXx]

I said "I do want adjustable current limiting"

 

[Hero999]

Sorry, my mistake.

I'm preparing a schematic.

 

[Reloadron]

I said "I do want adjustable current limiting"

I sort of figured you were in the US.

The transformer you want is **broken link removed** You do not want 220 Volt primary you want 115 - 120 Volt primary for US mains power. Look at the Triad F8-36 in the data sheet. Triad is just one example and carried by Allied Electronics as well as others and as well as other manufacturers.

You could as was mentioned go with a single not center tapped transformer and use a full wave bridge. I linked to the transformer you would want in the US but with a US mains primary.

The original circuit you posted will work and give you both adjustable voltage and current. I believe the transformer I linked to will work out for you.

<EDIT> A similar circuit could likely be built around the LM317 using fewer parts and effort so see what Hero has going. Anyway the transformer I linked to is what you want. </EDIT>

Ron

 

[xXAxHillbillyXx]

So is this basically what I need to do before the adjustable current limiting part is added? and i didnt change the companent values yet (I allready made the pic before I saw that you were working on a different schematic)
**broken link removed**

 

[Hero999]

Yes that's what you need to do.

I'll post the current limiter when I get time.

 

[xXAxHillbillyXx]

K, Thanx

 

[Hero999]

Here you go, it's not a perfect solution but it'll work.

 

[xXAxHillbillyXx]

Are d4 and d5 in the current limiting part just regular 1n400x diodes?
I worked on the schematic for a lil bit to clean it up and label all components.. is this correct as the final version?
**broken link removed**

 

[xXAxHillbillyXx]

I must be an IDIOT because I cannot find these dang transformers ANYWHERE! Dunno why but I just cant!

Edit: This is the closest I can find will it work?
https://www.mouser.com/ProductDetail/Hammond/186E28/?qs=sGAEpiMZZMv4oUrzpPKU3Ng7z4D4cZk%252bmePScM68TlU%3d
I looked at the data sheet and it shows it a dual 115/220 primary that I would could just hook up the 115 part, and it has a center tapped secondary which I could just bypass by putting my outs and the top and bottom of it and having nothing attached to the center right?
Here is the data sheet
https://www.hammondmfg.com/pdf/186E_data.pdf and by what I see I should be able to use this by just using pins 1,2,6 and 10

 

[Hero999]

Yes the diodes can be 1N4001 or 1N4148 it's not critical, any silicon diodes will do.

Tr1 can be any low power transistor which can handel at least 40V at 200mA e.g. BC327 or 2N2907.

Tr2 needs to be a power transistor e.g. BD437 or TIP41, and should be on a heat sink.

I found a couple of transformers, one is slightly cheaper than the other which has the advantage of being PCB mount. The datasheet will show you how to connect it up.

P-8617 Stancor Transformers
229D24 Hammond Transformers

 

[Reloadron]

I looked at the data sheet and it shows it a dual 115/220 primary that I would could just hook up the 115 part, and it has a center tapped secondary which I could just bypass by putting my outs and the top and bottom of it and having nothing attached to the center right?

No, in your example of the Hammond Transformer looking at the data sheet you would tie 1&4 together and 2&5 together for 120 Volt operation. You parallel the two 120 Volt primary windings. Yes as to the center tap. If you come off the secondary with a full wave bridge you don't use the CT.

**broken link removed** shows how to configure the transformer you linked to, the Stancore one.

This power supply won't be delivering over 1 amp to any load I assume?

Ron

 

[xXAxHillbillyXx]

oh yeah one last question.. C1 (in my schematic) can that capacitor be aluminum electrolytic? and is it actually supposed to me 4700uF, or 4700pF?

 

[Hero999]

I'm not meaning to be difficult but what do you think?

Try having a go at answering this for yourself and I'll confirm your answer.

 

[xXAxHillbillyXx]

I think it needs to be a 4700pF ceramic capacitor