I was thinking of putting a power on led across the caps to bleed them off, but im not sure if it will be necessary when the regulator circuit is built.

That's a good idea, if only for safety. You can also just put about 10K in resistance across each set to slowly bleed off the voltage. If you accidentally short the terminals of a 10000uF cap to something (including your hand) it will arc and blow a crater in it. I have tempered steel tools with permanent divots in them from this happening.

 

That's a good idea, if only for safety. You can also just put about 10K in resistance across each set to slowly bleed off the voltage. If you accidentally short the terminals of a 10000uF cap to something (including your hand) it will arc and blow a crater in it. I have tempered steel tools with permanent divots in them from this happening.

ive seen what 1 farad caps can do if charged wrong... my main thought about the led was for a soft turn off feature.. if nothing else it just looks cool... I understand your point about the safety of it though.. never occurred to me that a quick short could do real damage to a lot of thought and work.... Thanks

 

Another thing is I realize at some point im going to have to etch some pcb's, However I really want a retro look but with some modern to it. So would you advise for or against using the proper gauge wire in some aspects instead of putting the entire circuit on a single board? What I mean is I want to put the filter caps on a single board, and the actual regulator circuit on a different board and connect the 2 using a good 12ga. wire to connect the 2. And ive never used a power transistor like the 2n3055's before. it has only 2 legs and the collector is the case of it. So how am I to mount this to a heatsink without shorting the collector to the actual psu case?

 

It'll probably be fine, just remember to include the small bypass caps for the regulator...otherwise, they're sensitive enough that the induction of the wire can cause oscillations.

Re: the 2N3055, TO3 transistors are mounted with heatsink compound and a thin shield (traditionally mica, but you can get other materials, these days) that insulates the collector electrically while allowing thermal dissipation.

Looks like this.

 

so how would I make the connection to the collector?.. and ill have to remember to make sure to add the bypass caps when I draw the schematic..

 

also do I use the lm317 and 2n3055 to make the adjustable -v circuit also or would I need a different transistor for -v? and furthermore would I ever need a -24vdc 4a source for anything? Im not really sure what -v is even needed for except for some ic's and microcontrollers.. I just want to add it in the psu because im able to and I am trying to build a very versatile power supply for whatever projects I find myself doing in the future.. And the fact that I notice that the 2050 ic im using needs it.

 

the 2n3055 is an npn transistor right? so would I need a pnp for the -v side of the regulator circuit? and will the lm317 still work for it? I just had a new thought, Will I need to have a separate pot to adjust the + and - separately or will just 1 do both? I plan on using 2 of them anyways. 1 to get me close to my voltage and the other to fine tune it. This is the point where I start to get confused.

 

You usually use a screw and a nut to make the collector connection...and you'll need a PNP transistor and a negative regulator for the negative side. There's ways to dance around having a separate regulator, but I'm not sure they'd work at 4A of current...either way, you gotta have the PNP!

 

You usually use a screw and a nut to make the collector connection...and you'll need a PNP transistor and a negative regulator for the negative side. There's ways to dance around having a separate regulator, but I'm not sure they'd work at 4A of current...either way, you gotta have the PNP!

check out page 3 of this link.. would that be a better way to achieve what I want with less parts? at least for the +v side.. I have an extra sec. coil on my transformer that's 38.4vac/54vdc that I could use. I wasn't sure what I was going to do with it anyways.

http://www.ee.teihal.gr/labs/electronics/web/downloads/LM317T_Variable_Voltage_Regulator.pdf

 

That's a pretty cool circuit, but I'm not sure it achieves the goal of less parts...you're now using TWO banks of filter capacitors per side (one for the regulator and one for the pass transistors.) Those big filter caps are way more expensive than the tiny little parts a standard LM317 circuit uses!

Also, I don't think you should denigrate your negative rail...many op amps and most power IC's run better with two rails. So do AB transistor outputs. DC-coupling in general is hard to do without a +/- supply.

 

That's a pretty cool circuit, but I'm not sure it achieves the goal of less parts...you're now using TWO banks of filter capacitors per side (one for the regulator and one for the pass transistors.) Those big filter caps are way more expensive than the tiny little parts a standard LM317 circuit uses!

Also, I don't think you should denigrate your negative rail...many op amps and most power IC's run better with two rails. So do AB transistor outputs. DC-coupling in general is hard to do without a +/- supply.

point taken.. page 2 of that same link is the basis for my psu, just dual supply.. it claims 4a adjustable with just the 3 lm317's without the pass transistors.. so do I even need the pass transistors? and for the dual supply would I just use 3 lm317's on the -v side of things or will that change to because of the pnp-npn +/- thing?

 

I'm confused about the 3 LM317's...the document you posted shows a single-LM317 with a PNP pass-transistor inside the feedback loop on page 2.

Also, the document notes that getting 4A out of that circuit is dependent on ENORMOUS filter caps...a total of 36000uF per side!

The LM337 is a negative regulator that works exactly like the LM317 except for the other rail...see the attachment for an example (low-current, but the idea is generally the same.)

P.S...spending a little time with the datasheet for the LM317 and LM337 is a good idea...they have really helpful example circuits!

You can regulate both rails using 1 or more LM317's, but it involves creating a "false ground" using a resistor divider, an op amp, and a pair of transistors in class AB...it's imperfect and if you want this to be your definitive bench supply, it's worth the extra buck for the negative regulator!

 

Since the OP has multiple secondaries a more flexible approach may be to make a couple of independent positive supplies. They could then be used in series or parallel to provide higher voltage/ higher current/pos&neg supplies.....

Just a thought!

HTH Steve.

 

I'm confused about the 3 LM317's...the document you posted shows a single-LM317 with a PNP pass-transistor inside the feedback loop on page 2.

Also, the document notes that getting 4A out of that circuit is dependent on ENORMOUS filter caps...a total of 36000uF per side!

The LM337 is a negative regulator that works exactly like the LM317 except for the other rail...see the attachment for an example (low-current, but the idea is generally the same.)

P.S...spending a little time with the datasheet for the LM317 and LM337 is a good idea...they have really helpful example circuits!

You can regulate both rails using 1 or more LM317's, but it involves creating a "false ground" using a resistor divider, an op amp, and a pair of transistors in class AB...it's imperfect and if you want this to be your definitive bench supply, it's worth the extra buck for the negative regulator!

thank you thee 337 is what I was looking for.. the datasheet I have covers the lm117 and lm317.. no 337 on it. and the link your referring to is my example for a pass transistor. the other link I posted in post #1 page 25 example 55 shows the 3 lm317s.. and im willing to spend the extra money on whatever parts I need.. just figuring out what I need seems to be the challenging part.. ill download the 337 data sheet now..

 

Since the OP has multiple secondaries a more flexible approach may be to make a couple of independent positive supplies. They could then be used in series or parallel to provide higher voltage/ higher current/pos&neg supplies.....

Just a thought!

HTH Steve.

I have 3 secondary coils on my transformer. im using the sec. hv coil that has the center tap so I can have a dual supply. this coil after the rectifier and 10kuf 50v filter caps is 30vdc, the other 2 coils measure 8vac/11.3vdc and 38.5vac/54vdc.. the link I posted a couple posts back in page 2 shows a pass transistor. page 3 shows a high current supply using the hv coil to run the lm317 and another coil to power 2 2n3055's.

 

the schematic t03metalcan posted answers one of my questions. so ill use the lm317 on the +v side and the lm337 for the -v side.. I don't think im going to need as much current needs for the -v side as I will the +v side of the supply. I just need to figure out what I want to do on the +v side for my current needs.. As I understand from the datasheets a single lm317/337 I will only get 2a of current max.. Which I think will be fime on the -v side, but I really want at least 4a on the+v side.. Im starting to lean towards the page 3 example of using another coil from my transformer to power the 2 2n3055's..

 

The secondary with the center tap is fine for a +/- dual supply.

Use to 8VAC secondary to give you a 5VDC regulated supply.

 

The secondary with the center tap is fine for a +/- dual supply.

Use to 8VAC secondary to give you a 5VDC regulated supply.

that works for me.. now check out page 3 of this link. this is what Im thinking of using the 3rd sec coil of my transformer for..

http://www.ee.teihal.gr/labs/electronics/web/downloads/LM317T_Variable_Voltage_Regulator.pdf

 

sorry about asking so many questions,, I confuse easily and I only want to build this one time.. and I plan on using it as my main PSU. the one I have now works fine but it only gives me 700ma of current.. I routinely bench test car audio amplifiers (Im an automotive electric tech.) and my bench supply wont even turn on an amplifier. so I end up using the shops 10a supply, but find myself standing in line to use it to often.. anyways,, thanks for all the help.. I really appreciate it..

 

So the new parts on the shopping list include (3) lm337's and (3) 2n2955's right? If I use the 8vac coil to make a 5vdc regulated supply I have some DF01m 100prv, 1a (4-pin DIP) FW bridge rectifiers I could use for it. What size filter caps should I use on it? And could I use another lm317 to regulate it?