I guess it is safe?
wow!
rogerw
On 4/7/2022 10:34 AM, Geo Dowell wrote:
The photograph is of a model 07-451 X-Ray waveform
detector. Every X-Ray Service Tech in Scotland carries on in
his service case. You attach it via coax cable to an
oscilloscope and turn on the X-Ray machine. The detector sends
a waveform to the 'scope so its shape can be measured and
examined.
If the machine happens to have an?(green screen)?X-Ray
image intensifier, he can take a picture with a camera of
what's inside the detector . A bunch of diodes. The gaps are
where the junctions are, and you can see a faint outline of
the epoxy packaging on each diode.
From: "Roger Whatley"
<rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:58:24 AM
Subject: Re: [CDV700CLUB] Question and an interesting
site for those that modify CDV700s and more.
1) yes, could be
multiple junctions.
2) You have an
exray machine?
3) We used to
"de-pot" plastic packaged IC chips with acid to expose
the die in the package, to examine under a microscope,
photograph, etc. trace circuits that way....... might be
hard to do with an axial lead diode.... I don't know.
rogerw
On 4/7/2022 9:49 AM, Geo Dowell
wrote:
I've always assumed the multiple junction idea,
because in practice the higher voltage rectifier
diodes get longer and longer. Ones for a 100kV stack
are a good 6 inches long each. Don't know, just
guessing. Will have to X-Ray one, but when it's out of
the X-Ray machine how to do that?
Geo
From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:43:53 AM
Subject: Re: [CDV700CLUB] Question and an
interesting site for those that modify CDV700s and
more.
Well, the
answer to your first question is: I am not sure,
but I think it is probably just very lightly
doped silicon pn junction. The light doping (and
perhaps playing around with the doping profile -
Its just fizzicks, ya' know!) gives higher
reverse breakdown voltage. And the lighter
doping also gives a higher bulk resistivity such
that the extrinsic series resistance is higher
than a LV diode, so higher forward drop at least
is due to higher series resistance.
This is a
"no-cost" contract. It is going to take an
infinity of diodes!
rogerw
On 4/7/2022 9:32 AM,
Geo Dowell wrote:
Question Roger, are HV (like 8kV) low
current diodes a stack of normal PN junctions
inside? or are they a single special PN
junction? What I do measure is higher and
higher Fwd V drop as the V (sub) max rating
increases.
By the way, if you only need that many PN
junctions to achieve thermal cancelling, try
switching to Schottkey diodes. That will
double or tripple the parts count. This is a
"cost-plus-contract", right?
Geo
From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 9:06:12
AM
Subject: Re: [CDV700CLUB] Question and
an interesting site for those that modify
CDV700s and more.
Geo,
Sure,
enclosed, but I have already modified
the Zener String with a temperature
compensation scheme that will be
somewhat familiar to the discerning eye.
I am NOT suggesting this circuit for a
build, merely playing around with ideas!
So,
if I measure the voltage of the top of
that Zener String alone, it is a nominal
788V at 25degC, and 821V at 75degC, and
754V at-25degC. That is a +67V change
over 100degC or about +0.67V/degC
tempco. (parenthetically, the original
full Zener String was about +/-40V.)? If
I compensate that with the negative
tempco of a Vbe which is about
-2.2mv/degC,
I
need 0.67V/2.2mV = 304 Vbes...... whew!
That's a lot of diodes!
Instead
the BJT circuit is multiplying the sum
of Q1&Q3 Vbe by 129 = 258Vbe's. All
I can say about the difference from
calculated is that the actual tempco of
the bjt's is in the model somewhere and
differs from my Mindsim approximation.
And btw, the pnp BJT Q2 is a local
feedback trick that is "fortifying"
Q1...... without Q2 you get weak knee,
with Q2 you get a sharp knee. Q2 and R3
can be removed and the circuit still
functions but regulation suffers.
Anyway,
the second enclosure shows the
regulation performance over temperature.
When I expand the scale I can see the
regulated voltage at 906V nominal
25degC, 908V at 75degC, and 905V at
-25degC.
?
So,
for one thing, this whole exercise begs
a question: Who lets their GM Counter
get THAT hot or cold? I think that is a
philosophical question.... If a GM
Counter fell in the forest, in the
winter up north, and there was not a
woman there to turn it on, does it
really matter? Does it even exist???
?
rogerw
On 4/7/2022
3:36 AM, Geo Dowell wrote:
Roger, show schematic of sim?
Geo
From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Wednesday, April 6, 2022 9:28:41
PM
Subject: Re: [CDV700CLUB] Question and
an interesting site for those that
modify CDV700s and more.
Well I just simulated something I
had not yet thought to do...... I
simulated a Zener string.
Yeah, it worked...... ha!
Largest Zener I could find in the
model library was 36V so I strung
enough of those to make about 890V
nominal with a 3.3Meg dropper
resistor. Its regulation is very
flat only rose about 3V from 1000V
to 1200V input. That as good as my
Penultimate Way-Good Cascode Shunt
Regulator can do, and far less
complex.
But guess what? over temperature
it sucks big wind! +/-40V from -25
to 25 to 75degC! The Penultimate
only varies about +/-3V over that
temp range (overkill).
But the Good Enough Cascode Shunt
Regulator, with its temperature
compensation scheme, only varies
less tha +/-5V. Regulation varies
less than 10V from the knee to 950
to 1200V
On 4/6/2022 10:53 AM, Roger
Whatley via groups.io wrote:
Peter,
Minor change, I noticed after I
posted the note below that I had
not specified the second BJT in
the Darlington. The enclosed
schematic is corrected and now
the simulation predicts about
dead-nuts on for the tempco of
the output. Other than that,
same comments as below. I think
this is the best "good enough"
cascoded shunt regulator.
rogerw
On 4/6/2022 10:40 AM, Roger
Whatley via groups.io wrote:
Peter,Enclosed is a schematic
of my suggestion below. That
is an 8.2V Rohm Zener chosen
for tempco to cancel the
negative tempco of two Vbe's.
It is slightly too positive in
the result but quite "good
enough." You willr just get
much flatter regulation with
the Darlington pair and that
can be had in a single
package.
Of course, depending on the
Vcemax spec of your cascode
MOSFET, you might have only
one cascode instead of
two..... That will not make a
noticeable difference except
to breakdown.
rogerw
On 4/6/2022 8:32 AM, Roger
Whatley via groups.io wrote:
Peter,
I realize that circuit
described below might be
"good enough," but realize
that making that one BJT a
Darlington pair is a
significant improvement to
the regulation. You can even
get the Darlington in one
transistor package, of
course, cheap.
As UnRegHV increases, the
current in the BJT
necessarily increases in
order to regulate the loop.
For every extra 0.1uA of
extra base current required,
the voltage drop in the
feedback resistors (66M +
66M + 1M) goes up
0.1uA*(66M+66M+1M) = 13.3V
and thus regulation suffers.
The BJT current easliy goes
from less than 10uA to over
200uA, thus the base current
might go up by a worst-case
of as much as 1uA, giving a
133V change in the output.
So that is the motivation
for the Darlington.
(In case anyone wonders,
why not an FET instead of a
BJT, that WAS the original
circuit and it suffers worse
circuit errors.....)
The next big error is that
as the BJT current increases
with UnRegHV increases, so
does Vbe and Vz increase.
Those are the motivations
for subsequent circuit
complications and resulting
in the Penultimate
Way-Improved version..... it
is overkill, I know, to the
requirement, but by
simulating those
improvements I gain insights
as to just what the
remaining errors were. And
it was fun!
My take is that your
present circuit, but with a
Darlington Pair, will be
"good enough" and if it were
a purpose-built Darlington
in one three-lead package,
no more expensive or even
board-space than a single
BJT.
Of course, a single Zener
voltage may be chosen to
match the negative tempco of
two Vbe's. Again, no extra
expense or board space. (Off
the top of my head, I am
thinking about 8V Zener for
+4mV/degC?)
rogerw
On 4/4/2022 10:33 PM,
peter via groups.io wrote:
Roger:
?back to the circuit you
posted in message #300
Simple cascode, with only 1
npn tr + 2 mosfets.
Since I found the 2SK3265, I
removed the 2nd mosfet so
its very basic circuit.
66Meg, two 1 Meg, 100k+ 2.2M
trimmer , 5.1V zener,
2SK3265, 2SC3311
Set trimmer for 900V, Vary
input from 950~ 1150, output
only varied 5V or less.
Heated the circuit with a
hair dryer, got it up from
25C to about 60C, voltage
rose may be 5 or 6 volts.
Good enough for me!
Time to make it small enough
to stuff inside my CDV-700 !
It on the LHS of the
attached jpg, circuit in
message #300 is on the RHS
P
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
--
rogerw
On the Catclaw
收旬托次早 托式弛戎
The PanDemic is over, but the DemPanic goes on.
MisDisMal is a dictator's tool of repression.
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