> << My problem is that these resistors are not very common and
>  rather expensive (I need 2 because each unit will have
>  both a positive and a negative high voltage). >>
>
> Ruben,
> I assume you are going to pot this circuit as surface leakage will be a very
> large parasitic when you are using 500-1000M resistors. In either case, you
> could cut your cost in half by using a single resistor (2x the resistance)
> between the plus and minus voltage. I am interested to know how you make
> out...good-luck.
>
> Mark A. Corio

Yes it will be poted. The problem with one resistor is that it has to
withstand the double voltage. Also I think there will be a relatively
low ohm resistor in series with the 'bleeder resistor' to ground so I
can do some measuring of the output voltage.

>Paul Britton wrote

>You should really use 4 resistors ie 2 in each place for redundancy
>in case one goes open circuit, wouldn't want to kill anyone would
>we? What's the PSU for? Photmultiplier tubes, laser? or something
>else? Sounds interesting
>anyway.....later.........................Paul>

Im thinking of supervising the outputvoltage with a voltage divider,
which also means that I can check if the bleeder resistor is open
circuit.

The PSU is going to be used for discharging static electricity by
ionizing the air. It will be designed so it can't supply more than
3 mA which is considered safe for this kind of equipment.

>Lee McLaren wrote

>Normally in high voltage circuits you need physical seperation as
>well and electrical, what they do in tv high voltage circuits is use
>a large number of say 10 Meg ohms resistors in series and in a Z
>physical pattern so you get the physical seperation as well. Most
>resistors have a voltage rating as well as a power rating so you may
>have to use a larger number of resistors so that the individual
>ratings are not exceded. This will also give you some fail safe
>ability.
>
>regards
>
>Lee McLaren

>The Jacky's wrote

>Ruben  I've seen this solved by using a lot of cheap, comparetively
>low ohm, resistors in series.  This is also how we make test loads
>for HV power supplies...gj

Most 'normal' resistors have a voltage rating of a 250-500 Volts.
This would require 100 resistors to get a voltage rating of 50 Kv,
which is far too many for this design.

I asume that the stated voltage rating for a resistor is for open
air mounting. Since I am going to pot the bleeder resistor together
with the voltage trippler the voltage rating for each resistor
could be increased so that instead of 100 resistors I could perhaps
use 20 22Mohm resistors. Is this assumption correct?

Another idea I have is to put bleeder resistors across every
capacitor in the voltage trippler, which decreases the voltage over
the resistors. I havn't tried this yet though.







------------------------------------
Ruben Jonsson
AB Liros Elektronik
Box 9124
200 39 Malmo
Sweden
Tel +46 40 14 20 80
Mail: ruben@sbbs.se
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