Interesting Power Supply (fwd)

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Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Sat, 26 Mar 2005 17:42:29 +1030
From: Matthew Smith <matt@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Interesting Power Supply

Greetings

I acquired a "90kV" power supply from eBay some time ago; the supply 
consists of a PCB and a voltage multiplier unit.

The PCB has a pin-stip connector at one end and connections to the 
multipler.  An SG3524 drives a power transistor of some description that 
drives a "flyback" style transformer, perhaps quarter the size of a TV 
LOPT.  The transformer has a turns ratio (calculated by impedance 
ratio)* of 1:258.

The multiplier has three connections - A (I think ground), U~ (from the 
flyback) and M.  M (or it may be A - I forgot to note which connected to 
which) goes to a potential divider on the PCB which drives an op-amp - I 
assume that this is a feedback loop to the SG3524.  Multiplier is 
identified BG1971-000-6060.  Both multiplier and board are stamped with 
an "ERO" logo.  Writing is in German, but I can't get a response from 
www.ero.de...

One distintive feature of the multiplier (potted green lump) is the 8 
inch long fibreglass tube protruding from it; this shrouds the output 
terminal which is right at the bottom of the tube - makes me wonder 
whether if this thing really is supposed to put out 90kV.

Powering the board with 24V (pins identified by supply pins of SG3524) 
did nothing - there were probably enable pins and goodness knows what. 
I scrapped the board and decided to make up my own, simple controller.

Assuming oodles of losses, I'm guessing that the transformer will be 
putting out 4.8kV at a fairly miniscule current due to the tiny core size.

I have powered the multiplier with about 3kV from another flyback setup, 
with a metal rod in the multiplier tube, poking out just over the top. 
It made my hair stand on end (and there's a lot of it) and bits of dust 
and rubbish fly all over my desk.

QUESTIONS:

1) Has anyone come across anything like this or could hazard a guess as 
to its origins?

2) I don't know what sort of diodes they use in these multipliers; I've 
got some little integrated switchers I could use to drive it, but they 
work at 100kHz.  Would this be excessive?  (If so, I'll just run it at 
40kHz, using the original SG3524.)

I think I'll case it, with the tube coming out on top, with a drawer 
pull as an electrode.

Cheers

M


-- 
Matthew Smith
Kadina Business Consultancy
South Australia
http://www.kbc.net.au