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From: John Larkin on 22 Dec 2009 20:50
On Tue, 22 Dec 2009 20:33:54 -0500, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> 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. ;)
>

Oh, I have great respect for the 1B3, especially as a high-voltage
gain element.

John

From: Hammy on 22 Dec 2009 21:06
On Tue, 22 Dec 2009 10:18:04 -0600, "Jon Slaughter"
<Jon_Slaughter(a)Hotmail.com> 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.
>
>
Simplest soloution if you dont need high speed switching is something
like this.

VO1263

http://www.vishay.com/docs/84639/vo1263aa.pdf

http://canada.newark.com/vishay-semiconductor/vo1263ab/solid-state-relay/dp/93K1109
From: Tim Williams on 23 Dec 2009 02:59
"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message
news:gfq2j5dnr8opsgh9mitk2ld7op1502gavs(a)4ax.com...
> 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*

Not quite, it says it's a diode... Vf = 12V or so.

How do they make those, anyway? Are they monolithic? Even with a
wide-assed intrinsic region (PIN structure), I don't know of 10kV being held
off by a single junction. Besides, such a junction would have to be so
thick that diffusion effects within would not be negligible.

I can still imagine them being made monolithically, but laterally, so you
basically make a stack of PN's, shorting every other so it makes an
always-on SCR.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


From: Jon Slaughter on 22 Dec 2009 21:32
Hammy wrote:
> On Tue, 22 Dec 2009 10:18:04 -0600, "Jon Slaughter"
> <Jon_Slaughter(a)Hotmail.com> 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.
>>
>>
> Simplest soloution if you dont need high speed switching is something
> like this.
>
> VO1263
>
> http://www.vishay.com/docs/84639/vo1263aa.pdf
>
> http://canada.newark.com/vishay-semiconductor/vo1263ab/solid-state-relay/dp/93K1109

Thanks, That might do the trick. A bit expensive though for something that
seems relatively simple. The method they use with the fet for discharging
the gate might be all I need with any old optocoupler method.


From: Jon Slaughter on 22 Dec 2009 21:33
Jamie wrote:
> 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 have any recomendations? Only ones I have seen are for low voltage or
for switching only(rather than linear).

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