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-   -   LM317 experiments and measurements (http://www.diyaudio.com/forums/power-supplies/188975-lm317-experiments-measurements.html)

wintermute 9th May 2011 11:07 PM

Quote:

Originally Posted by wintermute (Post 2560745)
I tried to verify this on my breadboarded circuit, but my scope resolution was not good enough. I'm going to try a trick I saw another diy audio member do http://www.diyaudio.com/forums/power...filtering.html which is to record the rails of the PS and use an fft to view the harmonics, that may verify/debunk the results of my sims.
.

Well I've had some success using the above method, though I haven't got any plots to show just yet. The noise was actually quite good (after I realised I hadn't put in a jumper that grounded my adjust pin cap. I'd redone the circuit on the breadboard and missed it DOH).

Last night I completed the second reg on the breadboard (haven't tied the two together yet) and wondered why I was getting a -75db peak at 100Hz (whereas it was at -103db on the other reg circuit. Note that this is after being fed via a 10X gain preamp to the pc soundcard)..

After going over the circuit, I realized I'd placed the last 4700uF cap 1 pin off in the breadboard so it wasn't in circuit at all. I put it in the right spot, and the measurement was the same as for the other circuit. So from this I conclude that the extra filtering really does make a difference to the post output ripple.

I'm also going to make one reg with the standard resistive divider and compare to my circuit to see how much difference the bc560c makes. Hopefully should have all the results by the end of the week :)

Tony.

wintermute 11th May 2011 02:14 PM

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OK I thought I post a few results as I thought they were interesting :)

I haven't yet done any comparison between standard reg circuit and mine but thought that these comparisons of the difference that bigger caps pre-reg vs smaller and also with and without adjust pin bypass cap were worth posting!

Tests were done using my on board sound card as my Audigy seems to be playing up and I couldn't get anything resembling reality (everything was -117db regardless of configuration).

scope probe was connected to output and the ground pin on the last cap pre reg. I'm using a soundcard preamp set to 10X gain.

The pre reg filtration consists of 3 caps with 3.3r resistors between, ie CRCRC

The first pic compares 3 X elna silmic II 1000uf caps VS 1 X 10000uF Nichicon KG followed by 2 X 4700uF nichicon FW's.

left channel (white trace) is the 3 X 1000uF

The second pic compares the 1000uF 4700uF 4700uF with and without adjust pin bypass cap. I don't think I need to say which is which!!! adjust pin bypass cap is a 4.7uF polyester cap.

The third pic is a comparison between the preamp with scope probe shorted, and the output of the reg for the 10000uF 4700uF 4700uF config, just to give an idea of what contribution the reg is giving to the noise levels.

Fourth pic is the schematic of the reg circuit under test. I have only built half of the dual supply at this stage.

Tony.

agdr 11th May 2011 07:59 PM

wintermute: very interesting! I'm a fan of CLC and CRC pre-filters.

I see that you are using Fred Dieckmann's active adjust pin circuit.

http://www.diyaudio.com/forums/power...tml#post356154

I haven't tried it, but sounds like it works pretty well from the various posts I've read

wintermute 11th May 2011 10:20 PM

yes that's the one :) I've got the day off tomorrow so I'm going to reconfigure for standard operation and do the measurements again so I can get some objective measurements of what the effect is.

Note that at the moment the circuit is still on the breadboard so there is likely to be extra noise as a result. :) as you can see from the pic below, less than ideal ;)

http://static.diyaudio.com/forums/ga...m/DSC_7234.jpg

Tony.

gpapag 12th May 2011 10:19 PM

In terms of noise, these are excellent results.

When you will end up building these psus, it would be nice to do some more dynamic measurements with the intended load (amplifier) connected.

But this for later.

Thank you for sharing.

Regards
George

wintermute 13th May 2011 02:24 AM

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Thanks George! I just found another thing. Perhaps the first set of measurements should be taken with a grain of salt... The earth point I used for the scope probe in the first measurements was the lead of the last cap. If I take the measurement instead off the earth side of the load resistor the result is quite different, I guess this is a good indicator of how important layout is! There is probably a few cm's of wire between the leg of the last cap and the rest of the earth points on the bread board.

I took out the second cap to see what difference it made (after changing my probe earth point) and to my surprise it made no difference! put the earth probe back on the leg of the last cap and big difference!

1st pic is the exact same circuit, just the earth point moved for the two measurements. left channel is with earth point on the earth side of the 56R load resistor, right is with the earth point on the leg of the last cap. This is without the second cap in place.

Second pic is the comparison between with and without second cap except the scope earth was placed on the earth leg of the load resistor for both measurements! right channel is without second 4700uF cap. left has the second 4700uF cap. As you can see there is very little difference, the biggest difference is the spike at 62Khz which is actually worse with the second cap...

Third pic is comparison between 10000uF_4700uF_4700uF vi 3X 1000uF as per original post but with the different scope earth point... virtually no difference, and any difference could probably be put down to random noise...

So Whilst at first I thought that my Overkill was making a difference, it certainly seems now that it is not! I will now try with just a single 1000uF cap and no resistors to see what the result is, I have a suspicion it's going to be similar! I may have some spare caps for another project and a much simpler PS board as a result of these tests!

edit: I've just realised why it makes such a difference. Because I had the earth pickup on the actual leg of the cap, it would have been picking up the pulses that were going back through the resistors to the diode bridge, picking a point elsewhere in the circuit will not have this pollution. and one more pic ;)
fourth pic is comparison between 3 X 1000uF (with the 3r3's between) and a single 1000uF no resistors measurement point was across the load resistor. So this at least shows that the CRCRC does make a difference, even if my cap values were WAY overkill ;)

Tony.

gpapag 13th May 2011 02:33 PM

Hi Tony

Quote:

edit: I've just realised why it makes such a difference. Because I had the earth pickup on the actual leg of the cap, it would have been picking up the pulses that were going back through the resistors to the diode bridge, picking a point elsewhere in the circuit will not have this pollution. and one more pic
This is for to remind you, when you’ll do your final lay-out to have a look again at your posting :) http://www.diyaudio.com/forums/power...ml#post2487825 that is, do not forget to connect Q1 collector and ground sides of C8, U2 as close to your load as possible.

Quote:

Third pic is comparison between 10000uF_4700uF_4700uF vi 3X 1000uF as per original post but with the different scope earth point... virtually no difference, and any difference could probably be put down to random noise...

So Whilst at first I thought that my Overkill was making a difference, it certainly seems now that it is not! I will now try with just a single 1000uF cap and no resistors to see what the result is, I have a suspicion it's going to be similar! I may have some spare caps for another project and a much simpler PS board as a result of these tests!
That the 10000uF_4700uF_4700uF gives the same noise results at the regulators output (you may have a look at the difference on the input side) with the 3X 1000uF, is an indication that the LM317 is doing a good job.

Remember though that these results are valid for a fixed value load.

When the PSU will be connected to a variable load (Class AB/B amplifier), things may not be that easy for the LM317. *PS

So, please test this before you start removing caps from your final lay-out.

Regards
George

*PS: Unless you plan to use this PSU to feed a pure class A amplifier (which has constant current draw = acts as a fixed value load)

>Edit: Also make sure that the measuring signal coming into your audio card is of adequate amplitude (not very low), or else the spectrum measurements will not spell the real situation (I've done this mistake myself)

wintermute 14th May 2011 12:33 AM

Since I've pretty much Hijacked Uncle Pauls thread, I'm going to ask one of the mods to split this off into another thread :)

I think I'll call it "LM317 experiments and measurements"

I'll reply then George and post some more measurements as well :)

Tony.

wintermute 14th May 2011 01:17 AM

LM317 experiments and measurements
 
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I've decided to open this thread as I had Hijacked Uncle Paul's thread where he had questions about the LM317. http://www.diyaudio.com/forums/power...questions.html

I've built (at this stage on breadboard) a Dual rail +- 10V supply using only LM317's. The reg circuit is based on Fred Dieckmann's 1 transistor addition idea which he posted here http://www.diyaudio.com/forums/power...tml#post356154

The original design can be seen on my blog page here http://www.diyaudio.com/forums/blogs...011-02-10.html

Some follow up measurements are in this blog post, mainly showing the effectiveness of the CRCRC on the pre reg ripple. http://www.diyaudio.com/forums/blogs...-progress.html

I came up with this design using LT spice, It wasn't until I finally built it that I realised how much overkill the caps were ;) yeah in spice they made a difference but in the real world, those differences were so small as to be buried in the noise floor. Though as George (who\'s methods I\'m using to do these tests http://www.diyaudio.com/forums/power...filtering.html) has pointed out until I test with a real load I shouldn't discount the bigger caps outright.

Anyway I connected the two reg circuits together last night, and can happily say that I get + and - 10V and the noise performance remains as it did when measuring one or the other channels. There is a slight difference in the noise performance above 30Khz which I'm still trying to get to the bottom of, but this could be related to the implementation on the breadboard.

Attached are a couple of pics of the test set-up. first doing some measurements, and 2nd a close-up of the board, in this instance comparing the 10000uF R 4700uF R 4700uF set-up with 1000uF R 1000uF R 1000uF

I'll wait till I have got a mod to split of the other posts before I add anything to this thread :)

Tony.

wintermute 16th May 2011 12:35 PM

The best laid plans of mice and men often go awry
 
4 Attachment(s)
Well Post #9 was supposed to be the first post in this thread but due to the forums mechanics and the fact that my introductory post was more recent than any of the others it ended up last. Oh well :rolleyes:

So I did do quite a few more measurements, I'll post some more now.

1st pic is a comparison of the original 10,000uF_4700uF_4700uF vs 3 X 100uF caps. right channel is quite obviously the 100uF caps. As can be seen there is a point where the ripple pre-reg is just too much for it to be able to filter out.

2nd pic is a comparison between the bc560c version of the circuit and a bog standard LM317 implementation. Basically I took out the bc560c and the 1K resistor, and substituted in a 235 (actually 2 470 ohms in parallel as that is what I had on hand) ohm resistor for the 10K and a 10K pot for the 50K pot, and adjusted for 10V

From this it seems that the main difference the BC560 makes is at low frequencies. This makes sense as the RC filter formed between the 10K resistor and the 4.7uF cap has a much lower corner frequency (around 3Hz) compared to the 235 ohm resistor and 4.7uF cap (around 144Hz).

I wouldn't take the differences at higher frequencies too seriously, as the measurements were done on the two reg circuits as and a later measurement will show there are some differences between the two even when running identical setup.

The third pic shows the difference between an 11uF cap and a 4.7uF cap on the adjust pin with the BC560c Circuit. left channel is the 11uF cap, as you can see not a lot of difference. 4.7uF is polyester, 11uF is polypropylene.

The fourth pic shows the difference between an 11uF cap and a 4.7uF cap on the adj pin with the standard LM317 implementation. In this instance increasing to 11uF clearly does make a difference.

Well that's it for this post.

Tony.


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