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Why so many words about pass transistor?
Is  MOSFET rated to 800V 10A 240W is not ok for 350V 0.2A linear power supply?
No, no no!  It is called safe operating area.  Most MOSFETS are designed for switching operation, and are intended to be either fully ON, or fully OFF.  If operated in the linear region (between on and off) they do not share current evenly within the transistor's area, and the hot spot burns out.  There ARE MOSFETS designed for linear operation, mostly in audio amplifiers.  But, they are expensive, special parts, and not likely at all to be rated for 350 V.  (You'd expect to find them with 100 - 150 V ratings.)

Check the data sheets for the SOA rating of any FET you plan to use.  If not listed, try another part #.

OK, so I looked up the FCP650N80Z 800 V, 10 A continuous-rated FET.  The safe operating area chart shows that at 350 V, it can handle about 400 mA continuously.  Now, this would only be in the short-circuit condition, but a bench supply will experience that sort of incident on occasion.  So, as long as your current limit circuit will be able to pull the gate bias back fast enough, this one should work.

Definitely have more than one transistor handy while building your supply.

Jon
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Beginners / Re: Ngspice Polarity Question
« Last post by IanB on Today at 04:37:14 AM »
Why don't you verify what your spice simulation is giving you by looking at the resulting voltages at each node? For example, assuming V0 is zero, is V4 equal to +60 V or -60 V? Similarly, is V1 positive or negative?
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Other Equipment & Products / Re: Soldering Stations needs?
« Last post by sn4k3 on Today at 04:36:38 AM »
Yes, and i dont care about colour.

Now, must choose 1 shop xD

The cheaper one with most reviews and with B2 tip, easy  ;D
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Heres a heads up for the UK members especially if you're looking for a inexpensive function generator, then these might fit the bill, there's about 5 of these on offer at the moment from a company in Essex.
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Microcontrollers & FPGAs / Re: help! how to make a nsc800 computer?
« Last post by ali6x944 on Today at 04:32:52 AM »
Hi everybody,
it has been a while now, sorry for the late reply...
I was having problems with my scope as you know and I needed to send it to China.
It is fixed now, and again sorry for the late reply.
the circuit is not working properly the /PS line does not change at all, no matter what I do the /PS line stays at 5v...
I checked the connections and they seem alright, the 555 timer oscillates as expected, everything seems ok... :-//
quick question thou, is Y7/6/5/4/2/1/0 connected to anything?
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Hopefully its just a Tant playing up again, seems a common mode of failures with Tek scopes  ;D
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I got this Iphone PCB from Scotty (the "I built my own iphone guy") at Supercon - does anyone know why some BGA footprints are OSP and not gold ?
By best guess is it's to do with the metallurgy of the solder balls used on some of the devices
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Beginners / Re: Ngspice Polarity Question
« Last post by eev_carl on Today at 04:29:16 AM »
If I have n+ as 1 and n- as 0 for the Is polarity, then should I have n+ as 0 and n- as 4 for the Vs polarity in the schematic?  This is in accordance with the documentation, but I'm not getting the expected results of the current and voltage sources sending opposing currents across R2.
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Repair / Re: Splicing 20KV CRT high voltage cable help
« Last post by OmegaHyperion on Today at 04:28:42 AM »
The tape is 3M #23 high voltage splicing tape, its self bonding.

Sadly sending the device this cable is in to anyone is a no go, seeing as it weighs about 1 metric tone (literaly). I can practice on some RG11 coax cable, i think i have some high voltage cable of similar dimensions around my lab somewhere. Been a while since i worked with high voltage (well, other then testing a RG11 cable on my 50KV AC test stand today (i stopped at 35KV since it held what it needed to do, its to replace another 20KV cable in the same machine))

I didn't take a picture of the finished tape btw, the above image is the high voltage insulation only, not the outer most layer.

The cable is thankfully long enough to remove this crap connection and redo it properly.

The thing i found to be hard, was to keep the tape stretched, and wrap it around this highly flexible cable. I think i will use a jig next time to hold the cable better. Or just have a friend with me.

Just testing and seeing if i can see corona discharge is a no go, the power supply must not be damaged, no matter what.

If anyone is wondering what the voltage applied to this cable is, its 10KV DC. The other cable that will be RG11, is also going to have 10KV on it.


As to the shielding, ill need to figure something out there...
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Many years ago while on a course for LV operations (certification to work, live on 240 AC networks) we were shown a video in which a doctor said " If you are brought to me having suffered a severe electric shock then I will do my utmost to get your family here before the inevitable happens". Boy has that stuck with me. The sight of those cooked meat autopsy pictures sure teach you well. :)
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