livewire Posted June 4, 2011 Report Posted June 4, 2011 After having no success at all I tried this today with 3 x 160V zeners. It's still not working. The output voltage raises slowly. After 10 min it reaches 285V. Is it normal that the voltage across the zener diodes drops instantly if I want to measure it? Also the voltage across D7-D10 is IMHO too low. I get only 98V and not 580 V as expected. Just some "food for thought". Remember that I am not a master builder or EE, so my probing techniques may not be "textbook perfect" and somewhat brutish and primitive, but they get me to where I want to go. 1)Did you take steps to correctly insulate the heatsinked HV sand to avoid an arc path across the mounting screws? 2) Did you cut all of the traces (or lift/remove all of the associated parts) that I suggested before when you went with the zener string in lieu of the battery circuit? 3) Sounds possibly like some leaky capacitance at work here. ("output voltage raises slowly") If it were me, I would cut some traces and/or remove Q1, Q2 and Q8 and anything else that connects across the rails in order to isolate the filtered input stage and the bias circuit. I would then verify that the filtered DC was correct entering the bias circuit, and recheck the bias output for 580 volts. Divide and conquer. If the bias nows reads correct, test then replace the items you removed previously. (Or reconnect the cut traces) 4) As for the main power rails, how do they compare to one another? (static test and under power) I am assuming that #2 above was completed, because I have no way of knowing what is going on with the batteries. This could shed some light on different faults in the two curcuits.
rille Posted June 4, 2011 Report Posted June 4, 2011 @livewire The insulation is ok now, I used the thick insulators and plastic screws. Also all traces were cut. The problem is really the current source. A friend showed me an alternative current source with the BUZ80, which is easily to get here.
kevin gilmore Posted June 5, 2011 Author Report Posted June 5, 2011 Would like to see how you take an n-channel enhancement mode mosfet and turn it into a high side current source.
jcx Posted June 5, 2011 Report Posted June 5, 2011 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PVI5013RPBF-ND
El_Doug Posted June 10, 2011 Report Posted June 10, 2011 Excellence in engineering the alps or Kevin's design?
Horio Posted June 10, 2011 Report Posted June 10, 2011 Who's Kevin? Doug, you mind me asking where you picked up the RK50 from?
El_Doug Posted June 11, 2011 Report Posted June 11, 2011 (edited) got it from onlinecomponents since their communication is literally non-existent, I was hesitant to buy from them with a listed stock of 0. however, about a month ago i noticed "on order: 1" so I snatched it, figuring I could always have the credit card company cancel the payment (the price almost seemed like a scam - though it was $720 when I bought it, and now it's listed at $570). low and behold, it was real Edited June 11, 2011 by El_Doug
luvdunhill Posted June 11, 2011 Report Posted June 11, 2011 I've bought a lot of stuff from them, they are definitely legit.
luvdunhill Posted June 11, 2011 Report Posted June 11, 2011 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PVI5013RPBF-ND A few questions... Is CTR important? Is it better to let the base of the transistor float, or tie it to the opto? Looks like a good strategy for a 'stat amp...
purk Posted June 11, 2011 Report Posted June 11, 2011 (edited) got it from onlinecomponents since their communication is literally non-existent, I was hesitant to buy from them with a listed stock of 0. however, about a month ago i noticed "on order: 1" so I snatched it, figuring I could always have the credit card company cancel the payment (the price almost seemed like a scam - though it was $720 when I bought it, and now it's listed at $570). low and behold, it was real http://www.onlinecomponents.com/alps-electric_rk50114a0001.html?p=10114282 Is the link above the correct RK50 that I need to order? I want to purchase one for my T2 build? Thanks Edited June 11, 2011 by purk
Currawong Posted June 11, 2011 Report Posted June 11, 2011 I must have missed this when reading, but where are people getting their boards made?
luvdunhill Posted June 12, 2011 Report Posted June 12, 2011 I must have missed this when reading, but where are people getting their boards made? China typically.
jcx Posted June 13, 2011 Report Posted June 13, 2011 (edited) A few questions... Is CTR important? Is it better to let the base of the transistor float, or tie it to the opto? Looks like a good strategy for a 'stat amp... the gate drive opto isolators provide floating V ~8V from a string of photodiodes that you can series with the enhancement fet gate to get "depletion mode" equivalent - but the floating V source can provide very little current, < 10 uA - quite enough for mosfet gate drive though some C in parallel with the photodiodes assures enough charge capacity to soak up Crss slewing current - possibly a "gate stopper" R would assure RF stability http://www.irf.com/product-info/datasheets/data/pvi5013r.pdf noise and V ref stablity over temp, LED life are possible issues - depending on mosfet gate threshold V you should have enough V headroom to put a jfet or LM334 ccs in series with the mosfet source - pretty much eliminating concerns about the gate V quality that you would have if you simply used a source series R to set the current Edited June 13, 2011 by jcx
kevin gilmore Posted June 24, 2011 Author Report Posted June 24, 2011 (edited) Updated power supply board. Can run on less unregulated voltage, and has a multiplier for the bias. Parts reduced a bit, and a easy way to build it as a dual zener supply only. http://gilmore.chem.northwestern.edu/kgsshvps8e.zip Edited June 25, 2011 by kevin gilmore
livewire Posted June 25, 2011 Report Posted June 25, 2011 Mr KG, Are you going to post a schematic & overlay jpeg for your latest creation? When I have more time I'll whip out the gerber viewer to see wazzup.
kevin gilmore Posted June 25, 2011 Author Report Posted June 25, 2011 (edited) many thanks to kerry on this. http://gilmore.chem.northwestern.edu/kgsshvps8e.pdf http://gilmore.chem.northwestern.edu/kgsshvps8e.jpg Edited June 25, 2011 by kevin gilmore
Kerry Posted June 26, 2011 Report Posted June 26, 2011 I had a chance to prototype Kevin's new power supply. Here's a picture of my prototype... I've built the bias as well (on the top of the supply). My supply is set for 425VDC and the AC input is 355VAC. Here's a shot of the scope while I was measuring for noise on the 425V rail. I took several shots and this was the worst of the bunch. The amazining thing is that here is a shot of the scope when the power supply was turned off. I have a bunch of 2MHz noise in my appartment so I filtered that out before I measured. It really is a great supply.
ujamerstand Posted June 26, 2011 Report Posted June 26, 2011 All this progress makes me happy. I wrote a bom parser/generator tonight. There are two C17s in the pdf, one near lt1021, one in the bias supply.
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