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
how to separate ground potential
Started by ●October 16, 2008
Reply by ●October 18, 20082008-10-18
Reply by ●October 19, 20082008-10-19
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>): > >>> 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
