how to separate ground potential

[Charlie Springer]

On Sat, 18 Oct 2008 10:42:42 -0700, whit3rd wrote
(in article
<7f356697-56f9-4e2b-9da1-60e1b27044cd@26g2000hsk.googlegroups.com&gt:

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV.

This is the same sort of problem as electron microscopes (and
even microwave ovens) have in driving the filament. The easy
solution is to box up a 6V battery and regulate down to 5V.
The commercial solution is a custom-made, tested, transformer
that safely holds off 4 kV. It's likely to be potted (embedded
in a blob of tar or silicone).

You don't want any of the 4kV parts outside a shielded and
interlocked enclosure, of course...

There are neon signs all over the place, often within reach of drunks
......... ?

-- Charlie Springer

 

[legg]

On Fri, 17 Oct 2008 09:02:50 +0300, Paul Keinanen <keinanen@sci.fi>
wrote:

On Thu, 16 Oct 2008 17:49:25 -0400, legg <legg@nospam.magma.ca> wrote:


You haven't indicated the voltage and power requirement for this
housekeeping supply.

At lower power levels, some simple self-constructed solutions are
possible.

At very low power levels, just send optical power up on an optical
fiber and the data down on an other fiber.

This system is used on some high voltage measurement instruments
hanging on an overhead high voltage line.

If the OP would care to respond with the actual requirements, we'd

know if this was a candidate.

RL

 

[Paul Keinanen]

On Sat, 18 Oct 2008 17:12:48 -0700, Charlie Springer
<RAM@regnirps.com> wrote:

On Sat, 18 Oct 2008 10:42:42 -0700, whit3rd wrote
(in article
7f356697-56f9-4e2b-9da1-60e1b27044cd@26g2000hsk.googlegroups.com&gt:

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV.

This is the same sort of problem as electron microscopes (and
even microwave ovens) have in driving the filament. The easy
solution is to box up a 6V battery and regulate down to 5V.
The commercial solution is a custom-made, tested, transformer
that safely holds off 4 kV. It's likely to be potted (embedded
in a blob of tar or silicone).

You don't want any of the 4kV parts outside a shielded and
interlocked enclosure, of course...

There are neon signs all over the place, often within reach of drunks
........ ?

The output impedance and hence short circuit current of the HV supply
is also on issue. A 4 kV 1 mA should not be that dangerous , unless
of course if there is a large (stray) capacitance at the power supply
output, which could store a significant charge, which could cause a
nasty electric shock flowing through your body. For instance the CRT
25 kV anode connection has quite a significant capacitance.

There are miniature neon signs within windows advertising a product,
in which the leads or connections could be touched. The short circuit
current is so small that it does not do any harm.

Other typical examples would be simple ionizer with about two dozen
rectifiers and capacitors in a voltage multiplier chain, fed directly
from the 230 V mains. You could touch the output of the chain, but of
course it is a good idea to have a 1 megaohm at the output to limit
the current in case of the extremely rare situation that _all_
rectifiers and capacitors would fail and you would have 230 V mains at
the other end of the resistor.

We do not know if the original poster is using such high impedance HV
source, but in that case using a high isolation transformer to feed
the 5 V side, the transformer stray capacitance (perhaps less than 10
pF) may feed 50/60 Hz hum into the HV line.

Paul

 

[John Fields]

On Thu, 16 Oct 2008 15:16:56 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Thu, 16 Oct 2008 08:40:17 +0200, "Saul Bernstein"
jiffylube@freenet.de> wrote:

Hi,

I have to design a printed circuit board for a high-voltage environment.
Hence, the "ground potential" of the board has to be on 4 kV. Du to the fact
that the absolute potential values don't matter, one could say that the 2 kV
are virtually my ground potential. The problem arises by reason of the power
supply. I have to power my board with 5 V and for the mains adapter ground
is really 0 V.

Can someone think of a possibility to supply my board with a mains adapter
(AC/DC 220V/5V) and translate between the two ground reference potentials?

---
If you need your +5V to ride on the high voltage, you could do it like
this: (View in Courier)

+--------------------------------------+
| PCB |
| 7805 |
| +----+ +-----+ |
220AC>-----+-----+ +--|~ +|-----+-----| |--+5V |
| | P||S | | |+ +--+--+ |
| | R||E | | [BFC] | |
| | I||C | | | | |
220AC>---+-|-----+ +--|~ -|-----+--------+-----GND |
| | | +----+ | |
| | | | |
| | +----------------------------|---------+
| | |
| | |
| | |
| | +------+ |
| +------------------|~ +HV|-----+---
| | |
+--------------------|~ -HV|---------
+------+

You'll need a transformer with high isolation, and if your high voltage
is 4kV I'd recommend a dielectric strength of at least 5kV from
secondary to primary and from secondary to core. More would be better.

Be aware that this is a dangerous circuit and you could easily get hurt
or killed, or cause someone else to get hurt or killed

---
Oops...

I'd intended for that to be held in abeyance until the OP replied with
an answer as to whether or not there were only the two mains connections
and the connection to the HV connected galvanically into the PCB, but
somehow it slipped out.

Phil nailed it as well.


JF