D-Noizator: a magic active noise canceller to retrofit & upgrade any 317-based V.Reg.

[jan.didden]

Elvee, nice idea! When I read the posts I thought, could you use another '317 to do the de-noise duty instead of the extra NPN? After all, from the outside the 317 is just a transistor with 1.2V Vbe on steroids ;-)

Jan

[Elvee]

Originally Posted by gpapag

Thanks Elvee.
The "Finesse" circuit works OK (and it can be adjusted)

Sure, it works, but not only can you adjust it, you need to, to suit the peculiarities of the target regulator: you cannot use the same setup for 50mA or 1A.

In addition, you improve one parameter at the expense of another.

My proposition is "one size fits all", and it will remain identical for any 317 used in a "regular" manner: it will of course not work with circuits that already have been augmented in a way or another, by including an opamp in the loop for example.
It also improves all the three key parameters at once: you don't need to compromise.
Finally, it is also minimally invasive and purely additive: no need to remove something or cut tracks.

Originally Posted by gerhard

OMG. A LT3042 with an external transistor to carry the dissipation is
> 40 dB better than any LM317, right from the start.
Circuit is in the data sheet.

You probably missed the title and the point of this thread: it is not about developing some kind of new revolutionary superreg, but about upgrading existing equipments using 317/337's, which certainly number in the millions, if not more.

All you have to do is lift the cover, stick a post-stamp-sized PCB somewhere using a double-sided adhesive or a dab of silicone, solder 3 connections and you are done. The worst you might have to do is to lift one side of a capacitor.
No rework or butchering of the existing PCB, and all the DC voltages remain the same to the mV.
As a result, and for a negligible cost, you get a ~30dB improvement on all three key parameters: 90dB of cumulated improvement.
How sweeter could it be?

Originally Posted by jan.didden

Elvee, nice idea! When I read the posts I thought, could you use another '317 to do the de-noise duty instead of the extra NPN? After all, from the outside the 317 is just a transistor with 1.2V Vbe on steroids ;-)

I love the idea, although it may be a bit circular: I need to think about it, for exactly three months + one week. It will then be perfectly ripe...

[esl 63]

Read this if you are interested in regulators. If you use lm317 in a vice way!!
I use this circuit a lot. You add some green LED´s, capacitor and a pre reg lm317.
Super quiet!!
Using 3-pin regulators off-piste: part 1

[Elvee]

Yes it works, it bring the noise gain to 0dB, but my alternative reduces it to -30dB (in AC only though)

[Vovk Z]

Does it need only BC337?
I made this circuit with BC547C and LM338 - and don't have good result. It works as usual, without extra PSRR.
I tried different R4, R5, R6 and different C2, C3, C4 (it is stable with C4 1 nF).
What voltage have to be on the Q1 collector? (I have about 3V). Thank you.

[Elvee]

Originally Posted by Vovk Z

Does it need only BC337?

No, certainly not: I have tested it with various types, including a BC547 (don't remember the selection letter), and all worked, but the 337 gave a marginally lower noise

I made this circuit with BC547C and LM338 - and don't have good result. It works as usual, without extra PSRR.

I would look for dry solders or similar problems. The circuit in itself is very simple and straightforward, and if all the E-caps are OK and correctly connected, it should deliver the goods

I tried different R4, R5, R6 and different C2, C3, C4 (it is stable with C4 1 nF).
What voltage have to be on the Q1 collector? (I have about 3V). Thank you.

3V is OK: it should be around 1/4 of the output voltage, but as long as the transistor remains in it linear domain, it ought to work.
Try disconnecting C3, and observe the waveform at the collector of Q1 at the max sensitivity of the O-scope: you should see a lot of noise.

Note that I only tested it on a 317, but the 338 should work exactly the same.
There has to be some silly material error somewhere.

There is little benefit in making C4 as small as possible: in fact, you can use 10nF or 22nF, it will make the circuit more tolerant (but won't solve the issue of non-functionality)

[Vovk Z]

I haven't done photos (I forget my phone at home, but my lab is at work). It is about 7x20 mm, with three 30-40 mm wires.
I tested it mostly at 12 V output, so 1/4 is 3 V - it is ok. Now, I have about 0.6 mV noise with or without de-noiser.
There is a DC/DC pre-reg (XL4016) before the LM338 - can it be a reason of high noise?
Thank you for help, will look for a silly mistake.
I think, I have to test this cirquit with linear power supply first (because dc/dc radiates hum).

[Elvee]

I think that what you see is noise induced, radiated or common-mode generated by the DC/DC.
A test with a linear supply will remove any doubt

[Elvee]

I have now remeasured the output noise in good conditions: it is <0.3µV in a 10Hz to 10kHz bandwidth;
nothing particularly exceptional, but it all depends on the auxiliary transistor, an ordinary BC337 in this case.
The figure could be improved by using a really high performance, low noise transistor

[Mark Johnson]

Elvee, I sent you sixteen really high performance low noise transistors by international post, in May 2016. Here is a picture: link

The figure could be improved by using a really high performance, low noise transistor