gary o

Has the pinout changed on a LM317T {TO 220} I have a little circuit on a piece of paper for years....I just knocked one up & having problems 1st it burnt th adjustment pot , not sure if lm317 blown yet...found a data sheet it seems the pin out is different to on my piece of paper .....tried it the other way, doesnt work but as I said chip maybe fried now....

Sadly Im not good with equations so I dont really understand the science of electronics.

I have a transformer mains in 2X14 volts out..... says on transformer .......I have 45 V AC comig out...I know theres no load , but is that right ?

When I connect my full wave bridge rectifier across the 45VAC I the have 40 V Dc.....Is that right ?

If I connect a 470uf capacitor across my 40 V DC i get 55Volts DC if I put a .1 UF across I get 62 volts...& is that right ?
I dont understand capacitors in PSU circuits...

Will the output voltage come down when I connect in this case my mic pre ?

 AS that too high for LM317 .....Is it ?

Im just trying to get to 24V regulated


gswan

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #1 on: February 05, 2009, 02:54:41 PM »
Sounds like you have a problem with your measuring technique. Go back to the start and verify the output of your transformer. It's labeled as having 2x14V secondaries? How are you connecting these secondaries? I don't know of a transformer that would have a load regulation of 60%. I would expect, for a small toroid, that you get around 30V across the 28V series connected secondary.

Connect 28V to a full wave bridge and you get around 40V. Add the filtering cap with no load and it will increase a little, maybe to 44V. Adding a 0.1uF cap will make no difference.

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #2 on: February 05, 2009, 03:13:12 PM »
Thanks for reply yeah I did connect in series Im afraid I dont quite understand how to work out the voltages tho.

I found the correct LM317 pinout & corrected the circuit.

Basically the 2x14V didnt put out 28V with the load & regulation added...fell well short , I found an old RS 2X15V tran connected in series put thru LM317 circuit and got nice clean 24Volts for my pre.

I may still have issues the tran got very hot ..... it says on the secondary Max load  per winding is 3 VA....my little pre is meant to draw around 80 mA.....It should be ok ...shouldnt it ?

Thanks for help.

gswan

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #3 on: February 05, 2009, 03:32:20 PM »
If it's a 3VA transformer with a 30VAC secondary then you can get 100mA from it.
If your mic pre is drawing 80mA then you are fairly close to the limit. Bear in mind that these small transformers will run hot, mostly core losses, with temperature rises of 40 degrees C quite common.

If you can find a 15VA transformer instead it will run much cooler and last much longer.

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #4 on: February 15, 2009, 07:21:50 PM »
Goin outa of my F***ing mind here just built a lm317t circuit for my fetboy copied a little vero board design I already had made and had working.....it doesnt work I put 30 V in out comes 50 V adjust the trimmer fries the trimmer...Im using same board same transformer and rectifier I rebuilt it .....same ....changed LM317....same redesigned board .....same....I made loads of these things..

Pin 1 Adjust
Pin 2 Output
Pin 3 Input

looking at the front of a LM317T so you can read the writing 1 is on left 2 is in the middle & 3 on the right

Can anyone confirm this please ....thanks

gswan

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #5 on: February 15, 2009, 07:41:07 PM »
Sounds correct. Double checked the NatSemi datasheet which shows ADJ - VOUT - VIN as you described.
Double check that there isn't a stray connection on one of your veroboard rows. If you are frying the trimmer then there's too much voltage across it (maybe full rail).

MartyMart

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #6 on: February 15, 2009, 07:42:28 PM »
National semiconductor LM317AT or LM317T pdf that I have is as you describe  1-adjust 2- V out 3- V in

Could vary on a different brand though, got the data sheet ??

MM.
"Success is the ability to go from one failure to another with no loss of enthusiasm"

owel

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #7 on: February 15, 2009, 08:34:01 PM »
Quote
I have a transformer mains in 2X14 volts out..... says on transformer .......I have 45 V AC comig out...I know theres no load , but is that right ?

When I connect my full wave bridge rectifier across the 45VAC I the have 40 V Dc.....Is that right ?

If I connect a 470uf capacitor across my 40 V DC i get 55Volts DC if I put a .1 UF across I get 62 volts...& is that right ?
I dont understand capacitors in PSU circuits...

Your readings sound out of whack. Are you switching the multimeters between AC and DC readings?

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #8 on: February 15, 2009, 10:42:17 PM »
Hey thanks guys thanks for help Im gonna put this a side tonght have a calm look at it tomorow.. Owel those voltages were my first transformer it didnt seem to work ....

Here what I have on this one ...on tran its says O 15V 0 15V so I connect in series but I end up with 38 V AC on AC setting on my DMM

Other side of my bridge rectifier with 470 UF 63V cap across it I get 51 V DC as measured on DC settin on my DMM

At this point can I just say I dont understand where all these extra volts are coming from and would like to learn.....I thought I wouldnt find anymore than 30V as my transformer says 15 V & 15 v ?
& if this is ok how does my LM317T cope i thought it only went up to 37V ? or is this my problem ? then again with my one out of three good boards it does work I can happily set my 10K trimmer to give me 24V DC for my pre amp, works great..

il have to find the link to the Lm317 circuit Im using & post here I will add this soon...

I also in the past made my phantom power supplier with a LM317 its been working since the 90s I dont understand how it gives me my 52 volts but it does and I want to make another one, I drew what I did back then for such a time as now as I did with the other Lm circuit so I fear it may not work too....Im running out of 317s

Anyway thanks for help il post circuit tomorow cheers

owel

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #9 on: February 15, 2009, 10:57:08 PM »
Okay...I see what you mean.

The 15-0-15VAC is most probably at full rated load. Unloaded, you get higher than 15VAC. In your case, it's 19VAC.

Wire them in series, you get 38VAC.

Rectify them, you get approx. 38V x 1.4 = 53 Volts DC.

Quote
how does my LM317T cope i thought it only went up to 37V ?

You can use 317s for higher voltages. What most people confuse is that it's rated only at 37VDC max.
No it's not... what the datasheet says is the  Input voltage - Output Voltage differential must not exceed 37Volts.

(If you do exceed this 37-38V differential, you'd find that the regulator wouldn't function correctly and will output a much higher voltage than your "computed" output voltage.)




Steve Hogan

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #10 on: February 16, 2009, 12:15:56 AM »
If you do exceed this 37 Volt differential you will destroy the LM317T.

It is good practice to always use the high voltage version of the LM317 -- LM317HV when building phantom supplies with 317 regulators..  ST makes it and it is cheap.  Use a 56Volt Zener diode clamp between input and output and don't forget the standard protection diodes.The input/output differential will be immediately and destructively exceeded if you accidentally short the output of a 48 Volt supply made with a regular LM 317.

For a good discussion of transformer ratings, rectifier types, etc. see the design pages in the downloadable transformer full catalog at www.signaltransformers.com.

Steve Hogan
The Sound Steward
www.soundsteward.com

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #11 on: February 16, 2009, 07:24:58 AM »
http://www.geocities.com/tomzi.geo/lm317/lm317.htm

http://www.tkk.fi/Misc/Electronics/circuits/lm317.html

http://www.elecfree.com/circuit/power-supply/supply-regulator-125-30v-1a-by-lm317/

my circuit is most like the third circuit I dont have D2 or th 12K resistor cant find my exact ciruit at the mo..

I think I understand the differential thing cheers....& next time I order LM317 might as well get HV version  as long as pinout is different....Gotta go an sing for some old folks now but will tinker with dam simple circuit later thanks for reading.
« Last Edit: February 16, 2009, 07:32:19 AM by gary o »

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #12 on: February 16, 2009, 08:08:30 AM »
One final question if my Lm317s are getting cooked when solder them in any idea what will happen ? all I get from this circuit is 48 volts if I adjust the trimmer when it gets to near either end it burns literally....Im tryin to find some sockets so I dont have to solder in LMs ...I was scareful tho but I just dont understand whats goin on..

Cheers

peterc

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #13 on: February 16, 2009, 08:22:42 AM »
Gary

Make sure you have a cap on the output of the 317when powering up. I have blown them when building a PSU stage by stage without having anything on the output. Preferably a resistor as well to draw few mA of current.

This is a feature NOT in the datasheet......  ::)

Peter
If opportunity doesn't knock, build a door.

Steve Hogan

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #14 on: February 16, 2009, 09:11:26 AM »
The first 2 circuits are totally unsuitable for audio (or anything else for that matter) and leave out many parts you should leave in.
The circuit in the third link is much better, but a couple of points must be made.  PCB layout and or perfboard wiring is critical to get any Voltage regulator circuit to work correctly.

1. Do not use the PCB layout in the third reference. The layout allows probably 10 times (20dB) more ripple than necessary because of the way the ground trace is arranged. For low-ripple operation, the layout MUST have direct, FAT TRACE connections as follows:  Transformer to Bridge Rectifier Diodes.  Rectifier Diodes to Positive and Negative terminals of main Filter Cap (1000 uF in link #3). The Input terminal of the 317 should connect to the Positive terminal of the main filter cap thru a separate trace, and the Regulator Output ground connects to the Negative terminal of the filter cap with a separate trace.  The transformer/rectifiers charge up the main filter cap in short VERY high current pulses that will cause voltage drops in the PCB traces no matter how fat they are, so you give this pulsing circuit its own path from transformer thru the rectifiers thru the CAP and then back to the transformer.  The regulator circuit ground STARTS at the negative terminal of the main filter cap and goes to the output terminal of the regulator.  All the regulator grounded references (The lower voltage set resistor and the reference filter cap must be attached to the output terminal, or even better the negative pin of the output filter cap (470uF in ref 3) by a separate trace so that the ripple flowing in the high current filter cap charging loop doesn't infect the regulator output with ripple.

2. All these regulators show a 220 Ohm or 240 Ohm reference resistor. This resistor loads the regulator output with 5 mA.  The LM317 requires 10 mA minimum load. To make sure the regulator operates with no external load applied or very light loads, use 121 Ohms here and approximately 2.2K total resistance between the output common and the LM317 adjustment terminal for 24 Volt output.  The bottom (2.2K) resistor should connect directly to the negative terminal of the 470uF output cap thru its own trace -- not a big fat ground trace. The 121 Ohm resistor should be wired between the output and adjustment terminal of the 317 by the shortest, most direct connection possible.  All the protection diodes must be there but their connection locations are not critical since they only work in case of "emergency". There is no bleeder resistors shown in any of the schematics to discharge the supply caps when unloaded.  A 4.7k 1.2 watt resistor across the output terminal will draw 5 mA and discharge the supply caps when the supply turns off and is not connected to the audio circuitry.  With the resistor in place, one can then use the 220/240 Ohm reference resistor because the 4.7k bleeder resistor provides the other 5 mA of required load.

3. Use 100 uF instead of 10 uF for the adjustment filter.  Its negaive terminal should also attach to the output cap ground by its own trace (or it can be wired in parallel with the low side of the 2.2K adjustment resistance.

4. When applying the zener clamp for a 48V supply, connect a 5 Watt, 56V zener with the cathode (banded) end pointing towards the regulator input and the anode end connected to the regulator output.  Do not leave out D2.  The zener is wired in parallel with it. The protection diodes should be 1N400x types.

5.  All the circuits referenced show the lower resistor as a wide ranging pot (1.2Volts to 30 Volts).  If you know you want 24 volts then you need about 2.2K total.  So use a 2K resistor in series with a 500 Ohm pot wired as a rheostat -- connect 1 end to the wiper.  This gives you a much smaller adjustment range that will allow you to easily dial in the exact 24 volts.  The total resistance is 2.0k with the pot rotated to minimum so the wiper shorts out the pot and 2.5k with the pot rotated to max voltage with all 500 Ohms of the pot in series with the fixed resistor. Never use the wiper of the pot as a direct output, as shown in ref 1.  Always connect it to one end, to limit the maximum resistance due to an open wiper or even a scratchy pot.  The connection in the first reference is dangerous as an open on the wiper will allow the regulator to go all the way up to the unregulated voltage.

6. PCB, perfboard layout or even point to point wiring of the power supply is critical to good performance of any 3-terminal regulator.  A bad layout can cause the regulator to output volts of ripple.  I have reworked Power supply PCB's on commercially built supplies that had layout errors that caused excessive ripple.  KT DN780 and SW Series 20 original supply are two that come immediately to mind. A simple 3-terminal regulator circuit may not seem hard, but there is more to it than meets the eye.  Just connecting up everything according to a schematic will seldom give the performance you want.  Unless you really want this as a learning experience, consider purchasing a linear supply made by International Power  or Condor or Power-One.  Their PCB layouts are correct, their transformers are properly sized, and they are relatively cheap.
Steve Hogan
The Sound Steward
www.soundsteward.com

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #15 on: February 17, 2009, 08:12:51 AM »
Thanks guys thanks Steve for such detailed post, lots of good tips there......Ive just breadboarded my original circuit for now minus protection diodes & its working just to proof Im not insane, I must have been frying the LM317s when soldering....gonna add protection diodes & steves 4K7 bleeder resitor plus swap the 10 u for 100 U cap..a 2K2 fixed res in place of trimmer gave me 29 V....put trimmer there for now measures 3K8 when set at 24 V ruff, gonna do Steve suggestion of fixed res & small trimmer.

I wasnt gonna get that PCB from one of my links & had no idea it would be no good....As I say Iv been using a circuit similar to my 3rd link for a few years had no idea PSUs were this critical I have this circuit for a C28A valve mics 6.3 V heater supply and a DIY elam mics heater also for a DIY La2As heaters 12.6 V also for a DIy BA6A octal heaters and about 8 valve pre too I dont have any hum from this circuit as Iv built my bits and bobs I test well listen as I go disconnecting the various supplies while listening......Are tube heaters less likely to pick up ripple ? my little circuit is on tiny 4 track vero board.

Anyway il do the same for this feyboy il power it with battery and then see if the vero PSU adds anything bad thanks for help.
« Last Edit: February 17, 2009, 09:49:42 AM by gary o »

gary o

Re: LM317T confusion Pinout question ? & Power Supply questions ???
« Reply #16 on: February 17, 2009, 06:14:25 PM »
Ok all is working now just gotta add bleeder resistors I now have 2X 24 V supplies each has its own winding from transformer and its own rectifier and smoothing cap, I wanna connect in series so I have 48V for Phantom power & 24V for pre amp....anyone see a prob in doing this..? thanks


 

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