| Author |
Message |
Tom Hubin
Guest
|
 Posted:
Sun Nov 13, 2005 1:35 am Post subject:
10kv, 10ma, 1ms, switch |
|
|
Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
|
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 |
ehsjr
Guest
|
| Posted:
Sun Nov 13, 2005 1:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
Tom Hubin wrote:
| Quote: | Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
|
You can't do it. RC = 2 mS
You'll need to change your values.
Check here for the switching:
http://www.mmjp.or.jp/peec/ehvtsnew01.htm |
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Fred Bloggs
Guest
|
| Posted:
Sun Nov 13, 2005 1:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
Tom Hubin wrote:
| Quote: | Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
|
The cheapest approach would be to stack say 15x 1000V 1A Teccor SCRs,
these are cheap, and use say 10K gate-cathode pulldowns. Then you would
have to wind a 15 secondary pulse transformer to fire them- your current
is so small it won't make any difference how the stack collapses. The
tricky part here is that you don't have enough "holding" current to
maintain SCR conduction, and the way around that is to inject a
continuous current into the gate which makes the SCR act like a high
beta transistor or artificially boost the conduction current. There are
several ways to do that- one is make the transformer with large enough
VT product to sustain a 1ms pulsewidth, and a second is catch the top
stack SCR anode with current injection from a low voltage supply through
an HV diode that supplies the required holding current when the stack
has collapsed. Remove the pulse or remove the LV supply current and the
SCRs recover provided the voltage recovery on the 0.002u is not too
fast. But if that's the case, other things can be done to get around
that. It is basically a Radio Shack grade project.
|
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Martin Riddle
Guest
|
| Posted:
Sun Nov 13, 2005 8:46 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
I've seen a similar approach using stacked MOSFETS. But I believe it was fairly slow, in that each gate was turned on in a cascaded
fashion.
Cheers
"Fred Bloggs" <nospam@nospam.com> wrote in message news:43767FF9.7020803@nospam.com...
| Quote: |
Tom Hubin wrote:
Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
The cheapest approach would be to stack say 15x 1000V 1A Teccor SCRs,
these are cheap, and use say 10K gate-cathode pulldowns. Then you would
have to wind a 15 secondary pulse transformer to fire them- your current
is so small it won't make any difference how the stack collapses. The
tricky part here is that you don't have enough "holding" current to
maintain SCR conduction, and the way around that is to inject a
continuous current into the gate which makes the SCR act like a high
beta transistor or artificially boost the conduction current. There are
several ways to do that- one is make the transformer with large enough
VT product to sustain a 1ms pulsewidth, and a second is catch the top
stack SCR anode with current injection from a low voltage supply through
an HV diode that supplies the required holding current when the stack
has collapsed. Remove the pulse or remove the LV supply current and the
SCRs recover provided the voltage recovery on the 0.002u is not too
fast. But if that's the case, other things can be done to get around
that. It is basically a Radio Shack grade project.
|
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Tim Williams
Guest
|
| Posted:
Sun Nov 13, 2005 9:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
"Tom Hubin" <thubin@earthlink.net> wrote in message
news:43764968.6F1B@earthlink.net...
| Quote: | The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
|
I'm sure you can find a thyratron rated for 10kV or more without needing an
absurd current level (most thyratrons that size are going to be in the
kiloampere range...). If nothing else you can build an ignitron, though
that kinda seems overkill.
More common thermionic devices, hum a sweep tube might do that (possibly
with an external high voltage seal, most are rated for only 7.5kV peak,
dunno if that's when the inside or outside arcs over). Sweep tubes are
cheap and plentiful and most can sink several amps peak. Of course, you
need to apply control grid voltage for the duration of the pulse, and keep
it negatively biased the rest of the time.
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms |
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Winfield Hill
Guest
|
| Posted:
Sun Nov 13, 2005 5:35 pm Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
Martin Riddle wrote...
| Quote: | Fred Bloggs wrote ...
Tom Hubin wrote:
Values in this example are nominal just to explore component choices.
I have a 0.002uF capacitor charged to +10kV and would like to dump
most of that 100mJ into a 1Megohm load in 1ms. Max current would
then be 10mA. Constant current or decaying current are both options.
Rep rate would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open
for the rest of the period but I doubt that I will find a relay that
is accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10kV and 10mA.
Any suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
The cheapest approach would be to stack say 15x 1000V 1A Teccor
SCRs, these are cheap, and use say 10K gate-cathode pulldowns. ...
I've seen a similar approach using stacked MOSFETS. But I believe
it was fairly slow, in that each gate was turned on in a cascaded
fashion.
|
I don't think SCRs or thyratrons would be well suited for dealing
with such small currents. As for MOSFETs, they can certainly be
made to work quickly. For convenience, consider a series stack of
optically-coupled SSRs made from MOSFETs. Aromat NAiS makes the
AQY214EH, a 400V part with the H-type 5kV insulation. This has
0.5ms switch-on time and 0.08ms off time. And there's a slower
AQV254H with 1.8ms on time. DigiKey has both of them in stock.
[ NAiS also offers 1kV and 1.5kV relays (the AQV259 and AQV258),
but sadly they're limited to modest 1.5kV insulation ratings.
Ditto for all their 600V parts. Maybe another manufacturer? ]
One healthy property of FETs, and a serious advantage in this
case, is their tolerance of avalanche breakdown, provided only
that the die power dissipation is kept below the specified limits.
This is important, because the switch-on and off times won't be
exactly the same for all of the series-connected MOSFET switches,
exposing some to an overvoltage for a fraction of a millisecond.
Back to the SSR's official 5000V input-output insulation rating.
One solution would be to modify the 10kV setup to +5kV and -5kV.
--
Thanks,
- Win |
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Fred Bloggs
Guest
|
| Posted:
Sun Nov 13, 2005 5:35 pm Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
The photovoltaic stuff is much too slow and too expensive. Something
like this would be cheap and provide pull-enty of isolation:
View in a fixed-width font such as Courier.
..
..
..
.. 15 x 1N4007
.. 50mA
.. HV>---+-------[1M]-----------+------|<|-|<|- - - -|<|--<-----LV
.. | | CS
.. | | 30V
.. | | compliance
.. === 15X |
.. |2N --- 300mA
.. | TYN1006 \ /---[150]-+||+--+--<--
.. --- (STM) --- |||| | 5V
.. /// | )||( - ___
.. | )||( ^1n4001 | |
.. | )||( | - -
.. | |||| | 10us
.. +----------+||+--+-------
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. | ||
.. | ||
.. --- ||
.. TYN1006 \ /---[150]-+||
.. --- |||
.. | )||
.. | )||
.. | )||
.. | |||
.. +----------+||
.. |
.. |
.. |
.. ---
.. ///
..
.. |
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Spehro Pefhany
Guest
|
| Posted:
Mon Nov 14, 2005 1:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
On Sun, 13 Nov 2005 23:19:31 GMT, the renowned Robert Baer
<robertbaer@earthlink.net> wrote:
| Quote: | Tom Hubin wrote:
Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
First a little math:
Time constant T=R*C or T=(10^6 ohms)*(2*10^-9 farads) = 2*10^-3
seconds. That means it would take *two* milliseconds to discharge about
63 percent of the energy. Therefore, it will be impossible to "dump most
of that 100mj into a 1Megohm load in 1ms".
There are a number of relays that can act in the millisecond region
(but those cannot stand off even 500V), and ways to impliment a
mechanical switch (which could withstand the 10KV) for closure that is
controllable to give 1mSec closure within a few percent on timing.
An SCR might work, but how do you propose to shut it off? It would
stay on until the current drops below its internal threshold in the tens
of microamp region.
One could do that by forcing the gate negative (but no more than 5V
negative so that the junction does not zener), but one must extract all
of the anoe current until the SCR itself goes off (all of the stored
charges inside are removed).
BTW, a relay *is* solid state (metal) !
|
Except for the mercury kind.
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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| Back to top |
|
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Robert Baer
Guest
|
| Posted:
Mon Nov 14, 2005 1:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
Tom Hubin wrote:
| Quote: | Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
First a little math: |
Time constant T=R*C or T=(10^6 ohms)*(2*10^-9 farads) = 2*10^-3
seconds. That means it would take *two* milliseconds to discharge about
63 percent of the energy. Therefore, it will be impossible to "dump most
of that 100mj into a 1Megohm load in 1ms".
There are a number of relays that can act in the millisecond region
(but those cannot stand off even 500V), and ways to impliment a
mechanical switch (which could withstand the 10KV) for closure that is
controllable to give 1mSec closure within a few percent on timing.
An SCR might work, but how do you propose to shut it off? It would
stay on until the current drops below its internal threshold in the tens
of microamp region.
One could do that by forcing the gate negative (but no more than 5V
negative so that the junction does not zener), but one must extract all
of the anoe current until the SCR itself goes off (all of the stored
charges inside are removed).
BTW, a relay *is* solid state (metal) ! |
|
| Back to top |
|
|
Robert Baer
Guest
|
| Posted:
Mon Nov 14, 2005 7:44 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
Spehro Pefhany wrote:
| Quote: | On Sun, 13 Nov 2005 23:19:31 GMT, the renowned Robert Baer
robertbaer@earthlink.net> wrote:
Tom Hubin wrote:
Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
First a little math:
Time constant T=R*C or T=(10^6 ohms)*(2*10^-9 farads) = 2*10^-3
seconds. That means it would take *two* milliseconds to discharge about
63 percent of the energy. Therefore, it will be impossible to "dump most
of that 100mj into a 1Megohm load in 1ms".
There are a number of relays that can act in the millisecond region
(but those cannot stand off even 500V), and ways to impliment a
mechanical switch (which could withstand the 10KV) for closure that is
controllable to give 1mSec closure within a few percent on timing.
An SCR might work, but how do you propose to shut it off? It would
stay on until the current drops below its internal threshold in the tens
of microamp region.
One could do that by forcing the gate negative (but no more than 5V
negative so that the junction does not zener), but one must extract all
of the anoe current until the SCR itself goes off (all of the stored
charges inside are removed).
BTW, a relay *is* solid state (metal) !
Except for the mercury kind.
Best regards,
Spehro Pefhany
I forgot; Mercury is a *planet*. |
|
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Spehro Pefhany
Guest
|
| Posted:
Mon Nov 14, 2005 8:34 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
On Mon, 14 Nov 2005 01:44:14 GMT, the renowned Robert Baer
<robertbaer@earthlink.net> wrote:
| Quote: | Spehro Pefhany wrote:
On Sun, 13 Nov 2005 23:19:31 GMT, the renowned Robert Baer
robertbaer@earthlink.net> wrote:
Tom Hubin wrote:
Hello,
Values in this example are nominal just to explore component choices.
I have a 0.002ufd capacitor charged to +10kv and would like to dump most
of that 100mj into a 1Megohm load in 1ms. Max current would then be
10ma. Constant current or decaying current are both options. Rep rate
would be single shot to 500 Hertz.
The ideal would be relay contacts closed for a millisecond then open for
the rest of the period but I doubt that I will find a relay that is
accurate and fast enough. Any suggestions?
An SCR would work if I can find one that will handle 10KV and 10ma. Any
suggestions?
Suggestions for any other solid state devices or vacuum tubes or
anything else that might handle the switching for this?
Tom Hubin
thubin@earthlink.net
First a little math:
Time constant T=R*C or T=(10^6 ohms)*(2*10^-9 farads) = 2*10^-3
seconds. That means it would take *two* milliseconds to discharge about
63 percent of the energy. Therefore, it will be impossible to "dump most
of that 100mj into a 1Megohm load in 1ms".
There are a number of relays that can act in the millisecond region
(but those cannot stand off even 500V), and ways to impliment a
mechanical switch (which could withstand the 10KV) for closure that is
controllable to give 1mSec closure within a few percent on timing.
An SCR might work, but how do you propose to shut it off? It would
stay on until the current drops below its internal threshold in the tens
of microamp region.
One could do that by forcing the gate negative (but no more than 5V
negative so that the junction does not zener), but one must extract all
of the anoe current until the SCR itself goes off (all of the stored
charges inside are removed).
BTW, a relay *is* solid state (metal) !
Except for the mercury kind.
Best regards,
Spehro Pefhany
I forgot; Mercury is a *planet*.
|
Wanna see one of its moons?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
|
| Back to top |
|
|
Rich Grise
Guest
|
| Posted:
Wed Nov 16, 2005 1:35 am Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
On Sun, 13 Nov 2005 23:19:31 +0000, Robert Baer wrote:
| Quote: | BTW, a relay *is* solid state (metal) !
|
No, it's not. The part that does the actual switching is the
air (or vacuum) gap. ;-)
Cheers!
Rich |
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lawlopez
Guest
|
| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
1. Relays generally eplloy air or vacuum so they can hardly be called
solid state.
2. If you use a discharge device you will need to commutate it or turn
it off.
This is often done by using a second device and a capacitor in power
control circuits.
Anther way which is often used in pulse radar sets is to use resonate
the output
capacitor.
Personally I'd use a trigered spark gap, but that's just me.
Another realistic possibility is to take a lower voltage pulse (say 500
volts) and just step it up to 10KV. This makes the parts on the
primary at a more tractable voltage level.
with a transformer. |
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lawlopez
Guest
|
| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
There are some high voltage shunt regulators but I'm not sure if they
are available.
6HZ5 is rated at 6KV
7235 is rated at 10KV
PD500 is rated at 25KV.
These are all from a parametric search on using the TDSL program from
http://www.duncanamps.com
There are probably much more modern devices available. |
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Mike Harrison
Guest
|
| Posted:
Thu Nov 17, 2005 5:35 pm Post subject:
Re: 10kv, 10ma, 1ms, switch |
|
|
On 17 Nov 2005 04:44:30 -0800, "lawlopez" <lopez@mv.mv.com> wrote:
| Quote: | 1. Relays generally eplloy air or vacuum so they can hardly be called
solid state.
2. If you use a discharge device you will need to commutate it or turn
it off.
This is often done by using a second device and a capacitor in power
control circuits.
Anther way which is often used in pulse radar sets is to use resonate
the output
capacitor.
Personally I'd use a trigered spark gap, but that's just me.
Another realistic possibility is to take a lower voltage pulse (say 500
volts) and just step it up to 10KV. This makes the parts on the
primary at a more tractable voltage level.
with a transformer.
|
You could maybe used a marx-generator type topology, using mosfets instead of sparkgaps for the
switches. |
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