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From: Michael A. Terrell on 23 Dec 2009 11:08

Phil Hobbs wrote:
>
> On 12/22/2009 8:01 PM, John Larkin wrote:
> > On Tue, 22 Dec 2009 12:25:11 -0500, Phil Hobbs
> > <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
> >
> >> On 12/22/2009 11:49 AM, John Larkin wrote:
> >> <snip>
> >>> [1] and I just saw an ad for a 10,000 volt photodiode.
> >>>
> >>>
> >>
> >> Probably a gassy 1B3. ;)
> >>
> >> Cheers
> >>
> >> Phil Hobbs
> >
> > http://www.voltagemultipliers.com/pdf/Opto-Diode%2001_12_09.pdf
> >
> > http://www.voltagemultipliers.com/pdf/OC100HG_11_05_09.pdf
> >
> > It looks like a surface-conduction silicon tube thing maybe, which can
> > be a little leaky. This looks like fun for, well, *something*
> >
> > With a CTR of 0.5, power gain is several thousand.
>
> Hmm, I've been doing a few things along that line myself lately...but
> not at 10 kV!
>
> >
> > I once worked with some guys who made a cone-shaped bulk silicon thing
> > that could be blasted from above with a high-power laser. It would
> > switch megawatts in nanoseconds.
>
> I vaguely remember seeing those. It was sort of a giant APD iirc.
> >
> > JT is starting to snort again. He should see a doctor.
>
> C'mon, you used to build stuff out of dead TVs and stuff too. ;)


Dead TVs? No, I'm pretty sure that was Dr. Frankenstein, when he was
exploring his feminine side...


--
Offworld checks no longer accepted!
From: Jamie on 22 Dec 2009 19:56
Jon Slaughter wrote:

> Is it possible to drive the gate of a high side n-ch mosfet using an
> optocoupler to isolate and float the gate w.r.t to the source and still
> be effective?
>
> I want to continuously control the gate of a high side n-ch mosfet to
> prove a variable resistance for a high voltage load.
>
>
> G = Gate, S = Source, D = Drain
> OE = Opto Emitter, OC = Opto Collector
>
> Vcc--D
>
>
> OC--R2--D
> OE--G
>
> G--R1--S
> |
> Load
> |
> Gnd
>
>
> The idea is simple, a resistor(R1) connects the gate to the source. When
> no current is flowing the gate is then held at the same voltage as the
> source and the mosfet is turned off.
>
> An optocoupler is added to control current through that gate/source
> resistor which will "bias" the gate relative to the source and allow
> turning on the mosfet. A simple simulation shows this works but I'm not
> use how useful it is. Some protection mechanism for the opto would be
> needed as well as driving the gate too high.
>
> The isolation is necessary because of the high voltage used. I'm not
> worried about the "speed" as this isn't used for switching.
>
>
>
It will work as long as you have some head room to bias the gate.

Also, you should use a limiting zener diode from the Source to the
gate to prevent over voltage for Vgs..

For example, if your fet has a full turn on of 10v's above the source,
you need to have at least that much head room from the supply that is on
the DRAIN side.

In all, it means your drain supply must have 10 or more volts then
you'll ever expect on the source. You also need to factor in loss via
other circuits like the opto-isolator. etc..

You really should look at a charged pumped isolated high side
driver.. It would save you a lot of work..

You could also consider a P channel on the high side :)

From: John Larkin on 22 Dec 2009 20:01
On Tue, 22 Dec 2009 12:25:11 -0500, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> wrote:

>On 12/22/2009 11:49 AM, John Larkin wrote:
><snip>
>> [1] and I just saw an ad for a 10,000 volt photodiode.
>>
>>
>
>Probably a gassy 1B3. ;)
>
>Cheers
>
>Phil Hobbs

http://www.voltagemultipliers.com/pdf/Opto-Diode%2001_12_09.pdf

http://www.voltagemultipliers.com/pdf/OC100HG_11_05_09.pdf

It looks like a surface-conduction silicon tube thing maybe, which can
be a little leaky. This looks like fun for, well, *something*

With a CTR of 0.5, power gain is several thousand.

I once worked with some guys who made a cone-shaped bulk silicon thing
that could be blasted from above with a high-power laser. It would
switch megawatts in nanoseconds.

JT is starting to snort again. He should see a doctor.

John



From: Phil Hobbs on 22 Dec 2009 20:33
On 12/22/2009 8:01 PM, John Larkin wrote:
> On Tue, 22 Dec 2009 12:25:11 -0500, Phil Hobbs
> <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>
>> On 12/22/2009 11:49 AM, John Larkin wrote:
>> <snip>
>>> [1] and I just saw an ad for a 10,000 volt photodiode.
>>>
>>>
>>
>> Probably a gassy 1B3. ;)
>>
>> Cheers
>>
>> Phil Hobbs
>
> http://www.voltagemultipliers.com/pdf/Opto-Diode%2001_12_09.pdf
>
> http://www.voltagemultipliers.com/pdf/OC100HG_11_05_09.pdf
>
> It looks like a surface-conduction silicon tube thing maybe, which can
> be a little leaky. This looks like fun for, well, *something*
>
> With a CTR of 0.5, power gain is several thousand.

Hmm, I've been doing a few things along that line myself lately...but
not at 10 kV!

>
> I once worked with some guys who made a cone-shaped bulk silicon thing
> that could be blasted from above with a high-power laser. It would
> switch megawatts in nanoseconds.

I vaguely remember seeing those. It was sort of a giant APD iirc.
>
> JT is starting to snort again. He should see a doctor.

C'mon, you used to build stuff out of dead TVs and stuff too. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs at electrooptical dot net
http://electrooptical.net
From: Jim Thompson on 22 Dec 2009 20:42
On Tue, 22 Dec 2009 17:01:37 -0800, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>On Tue, 22 Dec 2009 12:25:11 -0500, Phil Hobbs
><pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>
>>On 12/22/2009 11:49 AM, John Larkin wrote:
>><snip>
>>> [1] and I just saw an ad for a 10,000 volt photodiode.
>>>
>>>
>>
>>Probably a gassy 1B3. ;)
>>
>>Cheers
>>
>>Phil Hobbs
>
>http://www.voltagemultipliers.com/pdf/Opto-Diode%2001_12_09.pdf
>
>http://www.voltagemultipliers.com/pdf/OC100HG_11_05_09.pdf
>
>It looks like a surface-conduction silicon tube thing maybe, which can
>be a little leaky. This looks like fun for, well, *something*
>
>With a CTR of 0.5, power gain is several thousand.
>
>I once worked with some guys who made a cone-shaped bulk silicon thing
>that could be blasted from above with a high-power laser. It would
>switch megawatts in nanoseconds.
>
>JT is starting to snort again. He should see a doctor.
>
>John
>
>

I was _laughing_ at Hobb's suggestion of a 1B3 as a photo device.
Might actually work.

But, in matters photo-multiplication, I'm engaged in designing around
a Hamamatsu R8900... discrete circuitry, not integrated.

As for health, I've been two days running up and down a 12' ladder
trimming the Christmas tree, then this morning, unfortunately, working
16' up on a skylight in the kitchen that jammed open, madly working to
disassemble control arms before the thunderstorm hit... just minutes
after I got it closed :-(

And I'm just 2 months from the big 7-0. So I'm probably healthier
than you... or Slowman ;-)

(Though, I will admit, all that "laddering" left me with that gnawing
ache indicating that the right hip joint will soon need replacement.
I'd better hurry and get it done, on the leftist's dime, before Obama
declares me "surplus" :-)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

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