Fusor Forums

yes I was talking about reputable supplies not aliexpress or banggood both of the later sell knockoffs that generally take their specs from the original but the product is nowhere near the original
this also appies to components like gate driver ics mosfets, IGBTs, RF transistors, ZVS driver boards, just see what the tesla coiling people are saying ---STAY AWAY from the chinese junk you get exactly what you pay for --high priced rubbish

John,

Any chance you could find and share a link (Mouser or etc.) to the kind of supply you are talking about?

Or details of the manufacturer/model.

Rex
I'll try
I'm in lockdown still but there are people at work who know what we bought i'll see

After the final exams and some unexpected health issues, I'm finally able to continue working. I just got the inverters for a power supply like that demonstrated by Nathan Marshall, but before that I'm (again) revising the HV supply.

More specifically, I've found a way to use the blocking oscillator effectively: by connecting an appropiate sized capacitor across the primary (the winding between Vcc and the collector) the charging and discharging happens in a resonant way, thus the output waveform is really similar to a sinewave and the noise (using the same filter as before: another thing I have to optimize) is way down: I cant distinguish it from background (which is around 100mV). This is promising, because it's a stellar performance (with a relatively stiff output too) for very few components and a very low cost.

I'm also using this cheap chinese flyback transformer (https://www.ebay.es/itm/15KV-High-Volta ... Sw-89ZRPh7) (I say flyback because despite not having any specifications, it has two small pieces of paper separating the yoke). The turns-ratio is also really high so I can operate at really low primary voltages.
The only thing I have to figure out is how to regulate the output without including excessive noise. In the internet I've seen a transistor stealing current from the base of the original oscillator, but without lineal control that seems noisy. Any ideas?

As soon as I have everything figured out, I will post en extensive explanation (LTSpice simulations, schematics, etc)

After becoming tired of feedback compensation shanaenigans, poor regulation and spurious oscillations, i'm now looking to linear high voltage, maida style regulators.
I've even found the fascinating LR8, a one-package, 400V, cheap, linear regulator! Wow! Is there any problems or quirks (aside from power regulation) I should be aware of?

This linear regulator are toys, with terrible regulation under load and tremendously easy to pop. I have finished the supply now, using a classic series regulator with a HV transistor from a CRT TV.
If anyone is interested in pursuing low noise power supplies, GET A DIFFERENTIAL PROBE! I can not tell you how many times I've being fooled by common mode noise and how many hours wasted tracking inexistent noise supplies. If you don't have it, you are handicapped (like me). Short ground clips (use the tiny ground springs) and always triggering the scope on the input waveform are a must. If the "noise" also does not trigger, or/and changes amplitude changing the lenght or shape of the ground clip, then you should most likely ignore it.
And do some serious indepth reading about noise before going down the rabbit hole.

Sounds like you have a good grip on the effort related to noise. I bought a Tektronix differential probe system at a hamfest at a "silent key" sale of $10.00 (the sellers did not know what it was. It was listed at over a thousand dollars by Tek!!). It is a high voltage differential probe and can handle 1kv. Sweet! I have only needed it a couple of times since I bought it. You are right about triggering and grounding issues went poking about for noise. Did I mention, I hate noise!! I hate chasing it down.... Fortunately, noise is not an issue in most of my current work.

Richard Hull

Why not filter with a 2-stage RC filter, like what every preamp uses? Since the bias current is low the resistor values can be MOhms.

http://sim.okawa-denshi.jp/en/CRCRtool.php

Joe:

If you use a fluorescent lamp inverter and this filter (just like Jim Williams used) the noise will be indistinguishable from background. However I wanted to add feedback as to make the supply regulated, and it always seemed to introduce noise. As of right now, and trying to learn as much as possible about feedback compensation and such, and are experimenting with a simple circuit that seems to work, more or less.
One of my main learning points have been that you can not say simply "add feedback to make it regulated" to a noiseless supply and expect it to stay that way without additional care.

Feedback will cause instability if the gain loop crosses 0dB at more than -20db/decade

The problem is that I dont know the characteristic function of the CCFL-Inverter and bridge-filter themselves, so planning for compensation is, well, impossible.
The best I'm doing is inserting various capacitance values between the feedback and the output pin of the TL072 until the noise (which very clearly is caused by oscillations since by killing the bandwidht by putting 0.1uF at the output of the opamp eliminates it) goes down to acceptable levels and no oscillation is present.

Not impossible. It can be measured.

How can this be done?

This should get you started:

https://www.ti.com/lit/an/snva364a/snva ... 8718652691

If I understood correctly, my main objective using this technique is to observe the phase shift at 0db and make sure it is high enough (between 45 or 50 degrees).
If I make my function generator float, then the transformer is unnecessary, right?

Basically, yes.

I would use a cheap 120V to 12V 60Hz transformer.

Thank you very much!

Well, no mater what I do, I am not able to observe a sinewave on the scope. All I see is 50hz hum and the noise of the supply. I will have to try something else
EDIT: I also appear to have destroyed my last TL072, so until Monday, I'm not going to be able to do anything else
EDIT EDIT: Searching in my drawer, I found another TL072! Tomorrow will do more tests

Those FET front-end op amps....Great in working circuitry.....Need a pile to really experiment with. Thank goodness they are cheaper by the dozen or thousands. I just bought a pack of 100, 2N7000's....Great little TO-92, low end sub-microamp input mosfet for turning on stuff in the .1 amp range using the joule energy from a mouse fart. When the turn-on energy just isn't there, the 2N7000 is.

I have used the OPA128 op amp to make single IC electrometers. It takes only 75 fempto amps to tickle the input. On a scope trace, on a winter's night, in DC follower mode with a 4-inch diameter aluminum ball on the input, my cat padding across the rug 5 feet away drove the trace off screen. I had to stay real still to not move the horizontal trace more than .5 volts one way or the other. Even manual shorting out was tough as moving away after grounding sent the trace off screen. I see why my vibrating reed Kiethley gold electrometer head has a small needle grounding solenoid to facilitate a remote grounding arrangement from the instrument box and a 6 foot cable going to the remote head.

Richard Hull