On Nov 8, 7:55=A0pm, Joerg <inva...@invalid.invalid> wrote:> halong wrote: > > Hi all, > > > I have a 200 MHz clock signal to send across the barrier of 5 KV > > I'm thinking of some RF transformer - perhaps "air core" ... but can't > > find any good candidate > > Medical, defibrillator-proof? That's pretty much my home turf. I often > use ferrite toroids, mostly #43 material and sometimes #61. Then 2-3 > turns, bifilar winding. Bifilar is key here, without that it's not going > to work.A bifilar winding is a twisted pair-transmission line, so what Joerg is recommending is - in fact - a transmission line transformer, which is what you need for 200MHz.> One of the wires needs to be at least MIL-STD 22759 amendment 1 (5kV > tested). Aircraft suppliers have that. Then the usual, strict training, > assembly and storage requirements, all ECO'd, and yada yada. > > If it's done right you can see amazing bandwidths. I did one interface > (defibrillator-proof) where they needed 8nsec pulses and the slopes were > less than 2nsec. Pretty much limited by what the driver circuitry could > provide.But don't make the winding length longer than a quarter-wavelength - 20cm in this context - and terminate the transmission line with its characteriistic impedance, unless you can exploit a reflection from the end of the line.> "Air core" becomes feasible at that frequency. You could possibly have > loops on both sides of the board. But the compliance folks might have a > hissy fit it you can't furnish the required documentation for the > circuit board core material. A serious downside of air coupling is > radiated emissions which can hit you from behind during EMC cert.The core doesn't do much in a 200MHz transmission line transformer, more in broad-band transmission-line transformers that can handle components at 200MHz and above. -- Bill Sloman, Nijmegen
RF galvanic isolator ...
Started by ●November 8, 2011
Reply by ●November 8, 20112011-11-08
Reply by ●November 8, 20112011-11-08
Bill Sloman wrote:> On Nov 8, 7:55 pm, Joerg <inva...@invalid.invalid> wrote:[...]>> "Air core" becomes feasible at that frequency. You could possibly have >> loops on both sides of the board. But the compliance folks might have a >> hissy fit it you can't furnish the required documentation for the >> circuit board core material. A serious downside of air coupling is >> radiated emissions which can hit you from behind during EMC cert. > > The core doesn't do much in a 200MHz transmission line transformer, > more in broad-band transmission-line transformers that can handle > components at 200MHz and above. >The core takes care of the lower spectrum parts. That way you can get by with 3-4 turns on a half-incher. The only reason I usually can't go smaller is because the Teflon wire is so unwieldy and must be babied so it won't get bruised. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 8, 20112011-11-08
Bill Sloman wrote:> On Nov 8, 3:41 pm, halong <cco...@netscape.net> wrote: >> Hi all, >> >> I have a 200 MHz clock signal to send across the barrier of 5 KV >> I'm thinking of some RF transformer - perhaps "air core" ... but can't >> find any good candidate > > You want a transmission line transformer, made with coaxial cable that > can stand 5kV between inner and braid. Many can - Farnell lists an > RG58 cable good for 15kV (5mm diameter) and an RG174A got to 6kV > (2.54mm O.D.). >Careful. Two things: a. A sprawled out coax transformer can radiate like heck. Not good during EMC cert. b. There needs to be something in writing from the manufacturer, about the dielectric strength. Compliance engineers usually want that paperwork or may refuse to sign off. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 9, 20112011-11-09
On 11/8/2011 12:20 PM, halong wrote:> On Nov 8, 10:18 am, Tim Wescott<t...@seemywebsite.com> wrote: >> On Tue, 08 Nov 2011 06:41:54 -0800, halong wrote: >>> Hi all, >> >>> I have a 200 MHz clock signal to send across the barrier of 5 KV I'm >>> thinking of some RF transformer - perhaps "air core" ... but can't find >>> any good candidate >> >> Have you tried widening your search to just specify a 200MHz signal >> frequency and galvanic isolation? I think the 200MHz part isn't a big >> deal, but the galvanic isolation may be. >> >> If EMI is a concern then an air core transformer may not be a good >> choice: it's going to leak RF like a sieve, and the spacing you'll need >> for 5k isolation won't help. >> >> If your production volumes are low, anything that works right off the bat >> is way less expensive than you think -- engineering time costs money, >> after all. So you may want to at least price out your fiber optics >> solution. >> >> --www.wescottdesign.com > > Yup, optics, that would be my last planOf course you might have to _power_ something across that isolation gap, too. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●November 9, 20112011-11-09
Phil Hobbs wrote:> On 11/8/2011 12:20 PM, halong wrote: >> On Nov 8, 10:18 am, Tim Wescott<t...@seemywebsite.com> wrote: >>> On Tue, 08 Nov 2011 06:41:54 -0800, halong wrote: >>>> Hi all, >>> >>>> I have a 200 MHz clock signal to send across the barrier of 5 KV I'm >>>> thinking of some RF transformer - perhaps "air core" ... but can't find >>>> any good candidate >>> >>> Have you tried widening your search to just specify a 200MHz signal >>> frequency and galvanic isolation? I think the 200MHz part isn't a big >>> deal, but the galvanic isolation may be. >>> >>> If EMI is a concern then an air core transformer may not be a good >>> choice: it's going to leak RF like a sieve, and the spacing you'll need >>> for 5k isolation won't help. >>> >>> If your production volumes are low, anything that works right off the >>> bat >>> is way less expensive than you think -- engineering time costs money, >>> after all. So you may want to at least price out your fiber optics >>> solution. >>> >>> --www.wescottdesign.com >> >> Yup, optics, that would be my last plan > > Of course you might have to _power_ something across that isolation gap, > too. >Oh, that's easy. You let off a ton of press releases that you will use the super duper green-tech solar approach, then get some major loan guarantees, smile when the TV crews and the big brass from the hill is visiting. Then let the sun supply it. If it don't shine no more you just file for chapter 11 and start over :-) -- SCNR, Joerg http://www.analogconsultants.com/
Reply by ●November 9, 20112011-11-09
On Wed, 09 Nov 2011 14:26:20 -0800, Joerg <invalid@invalid.invalid> wrote:>> Of course you might have to _power_ something across that isolation gap, >> too. >> > >Oh, that's easy. You let off a ton of press releases that you will use >the super duper green-tech solar approach, then get some major loan >guarantees, smile when the TV crews and the big brass from the hill is >visiting. Then let the sun supply it. If it don't shine no more you just >file for chapter 11 and start over :-)Supply your own "sun" from a laser via an optical fiber to a solar cell. Return the measurement through an other fiber. Such tricks are used e.g. for phase current measurements on 400 kV (and above) HV lines.
Reply by ●November 9, 20112011-11-09
upsidedown@downunder.com wrote:> On Wed, 09 Nov 2011 14:26:20 -0800, Joerg <invalid@invalid.invalid> > wrote: > >>> Of course you might have to _power_ something across that isolation gap, >>> too. >>> >> Oh, that's easy. You let off a ton of press releases that you will use >> the super duper green-tech solar approach, then get some major loan >> guarantees, smile when the TV crews and the big brass from the hill is >> visiting. Then let the sun supply it. If it don't shine no more you just >> file for chapter 11 and start over :-) > > Supply your own "sun" from a laser via an optical fiber to a solar > cell. Return the measurement through an other fiber. Such tricks are > used e.g. for phase current measurements on 400 kV (and above) HV > lines. >But they won't give you a fat loan guarantee for that :-) Anyhow, I always ferry power over magnetically. It is very cheap and you can pump tens of watts to the other side if needed. That's kind of tough to do with lasers and solar cells. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 9, 20112011-11-09
Joerg a �crit :> upsidedown@downunder.com wrote: >> On Wed, 09 Nov 2011 14:26:20 -0800, Joerg <invalid@invalid.invalid> >> wrote: >> >>>> Of course you might have to _power_ something across that isolation gap, >>>> too. >>>> >>> Oh, that's easy. You let off a ton of press releases that you will use >>> the super duper green-tech solar approach, then get some major loan >>> guarantees, smile when the TV crews and the big brass from the hill is >>> visiting. Then let the sun supply it. If it don't shine no more you just >>> file for chapter 11 and start over :-) >> Supply your own "sun" from a laser via an optical fiber to a solar >> cell. Return the measurement through an other fiber. Such tricks are >> used e.g. for phase current measurements on 400 kV (and above) HV >> lines. >> > > But they won't give you a fat loan guarantee for that :-) > > Anyhow, I always ferry power over magnetically. It is very cheap and you > can pump tens of watts to the other side if needed. That's kind of tough > to do with lasers and solar cells. >But obtaining 1MV isolation from a small POE transformer (or even your custom one) is somewhat tricky :-) -- Thanks, Fred.
Reply by ●November 9, 20112011-11-09
Fred Bartoli wrote:> Joerg a �crit : >> upsidedown@downunder.com wrote: >>> On Wed, 09 Nov 2011 14:26:20 -0800, Joerg <invalid@invalid.invalid> >>> wrote: >>> >>>>> Of course you might have to _power_ something across that isolation >>>>> gap, >>>>> too. >>>>> >>>> Oh, that's easy. You let off a ton of press releases that you will use >>>> the super duper green-tech solar approach, then get some major loan >>>> guarantees, smile when the TV crews and the big brass from the hill is >>>> visiting. Then let the sun supply it. If it don't shine no more you >>>> just >>>> file for chapter 11 and start over :-) >>> Supply your own "sun" from a laser via an optical fiber to a solar >>> cell. Return the measurement through an other fiber. Such tricks are >>> used e.g. for phase current measurements on 400 kV (and above) HV >>> lines. >>> >> >> But they won't give you a fat loan guarantee for that :-) >> >> Anyhow, I always ferry power over magnetically. It is very cheap and you >> can pump tens of watts to the other side if needed. That's kind of tough >> to do with lasers and solar cells. >> > > But obtaining 1MV isolation from a small POE transformer (or even your > custom one) is somewhat tricky :-) >With series resonance in combination with some glass or porcelain it is feasible :-) But you have to stick to ISM or the Federales will waltz in. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 9, 20112011-11-09
On Wed, 09 Nov 2011 15:12:55 -0800, Joerg <invalid@invalid.invalid> wrote:>upsidedown@downunder.com wrote: >> On Wed, 09 Nov 2011 14:26:20 -0800, Joerg <invalid@invalid.invalid> >> wrote: >> >>>> Of course you might have to _power_ something across that isolation gap, >>>> too. >>>> >>> Oh, that's easy. You let off a ton of press releases that you will use >>> the super duper green-tech solar approach, then get some major loan >>> guarantees, smile when the TV crews and the big brass from the hill is >>> visiting. Then let the sun supply it. If it don't shine no more you just >>> file for chapter 11 and start over :-) >> >> Supply your own "sun" from a laser via an optical fiber to a solar >> cell. Return the measurement through an other fiber. Such tricks are >> used e.g. for phase current measurements on 400 kV (and above) HV >> lines. >> > >But they won't give you a fat loan guarantee for that :-) > >Anyhow, I always ferry power over magnetically. It is very cheap and you >can pump tens of watts to the other side if needed. That's kind of tough >to do with lasers and solar cells.While a 10-30 cm ferrite rod with a well insulated primary at one end and a secondary at the other end can transfer a lot of power, the distance between the primary and secondary is quite small, if we have to worry about lightning strikes.
