Continuing discussion here......
One open question in my mind is the tubes current regulation. It has been suggested that these supplies regulate the tubes current.
Its clear that the feedback circuit measures the current in the flyback primary and that adjusts the PWM. However I don't think that it really measures the actual current in the tube, unless there is some reflected effect from secondary to primary that I do not understand.
It seems to me that the current in the primary is a proxy for the current in the tube but not the real current, especially since the tube starts out as a high impedance and then goes negative resistance.
Also I do not know if you have seen this post regarding my attempts to see what is in the flyback.
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- I was going to encourage you to continue your tear apart. Now that you've seen photos of what's inside my similar transformer, you know where to dig and what to expect with yours. At this stage I was using a handheld Dremel with a router bit (sort of) and was removing encapsulation material to follow each component wire lead. Slow process and dusty (wear a mask!).
If you choose to cross-section the transformer windings, initially I used a bandsaw, and then a hacksaw, before milling the face flat and sanding and polishing it (to count the wires).
You know the capacitor and rectifier component count for mine. The number of diodes and capacitors you mention in your post don't match mine, so perhaps there's a different topology involved? Especially the 2 capacitors.
I hope you do better than I did regarding component part numbers. I'd love to know the HV rectifier number.
Your HV transformer may use only 2 rectifiers in parallel, while mine uses 3, because of the difference HVPS rating. My 80W claims 27mA (with 3 rectifiers in parallel). A typical 40W is good for 20mA (which might correspond to 2 rectifiers in parallel). That could be one explanation.
BTW, what is the manufacturer's part number on the transformers you have?
Do you have more photos? In the past I saw many more photos of your power supplies (beyond those used in your blog posting) in your photo stream, but I don't have a working link to your photos now. (Private Message me if you want.)
We await the results of the autopsy!2w
- That's my current theory: laser tube current out of the the transformer, tracks the regulated drive current into the transformer. I suspect they put on a test load, and then tweek the calibration pot (labeled "PL" for Power Level?). That makes up for all the component tolerances. The goal is to provide a transfer function such that a *IN *("intensity") input at 5V would produce a 20mA tube current output. Note that there are a lot of other nonlinearities involved here, but they may not be important, as the laser user visually adjusts the machine pot to achieve the desired result. So it's probably more important that the operation is stable rather than linear.2w
- Don KleinschnitzModerator+1funny how much on the same page we are. Yesterday I changed my mind and decided to do a second transformer.
Guess what I found out? Paint stripper seems to dissolve the potting ..... our resident genius chemist gave me that idea and at least on one sample it seemed to work. Needs to soak for quite a while, use gloves and leave outdoors. Multiple rinses and re-soaks are necessary. Will post pictures later today.
Now that I am on the same page on the current control I need to noodle how this drivers regulation acts when the tube enters ionization and the effect on the laser's power and in turn cutting and engraving.
What still makes we wonder is that when the tube ionizes the secondary must see a low impedance and very high current that is not really controlled by the primary drive. To me this is like suddenly putting a short on the output of a HV power supply.
Then again, perhaps the bridge and filter cap would reduce the effect on the secondary.
This starts to close the chapter on my hunt for proof around the response of the K40 laser control system. I suspect it is much longer than what the Smoothie-like controllers can dish out. Running PWM control signals shorter than about 400us significantly reduces the effective resolution when engraving. However increased PWM control freq. indirectly increases effective cutting power by repeatedly dumping high power pulses.
Here is the link to my LPS album:
photos.google.com - K40 LPS2w
- Don KleinschnitzModerator+1This is what I used.2w
- Don KleinschnitzModeratorDisolving......2w