1) Yes, I think so, but 10uA makes me much
more comfortable. At 1uA I would expect it is low in the knee.
At 10uA I would suspect it is high in the knee. That is all I
know about that: suspicions based on simulations.
2) No spec I have ever seen. You would prefer
the smallest (1/8 or 1/4Watt) Zener wattage? in order to be the
smallest junction area so that current density is as high as
possible.
3) yes, and that is why I was excited by that
2uA OpAmp. Essentially to duplicate the internal LM431
configuration but with very low current demand. But every
attempt I have made to use it in simulation has oscillated. Too
much phase lag thru the feedback? loop. I tried to frequency
compensate to no avail. I also tried a similar higher
gain-bandwith and 20uA version. No dice. If I kept going up in
current consumption I assume I would find a sufficient phase
margin for the loop, but that idea is on indefinite hold.
I like the Good Enough circuit just fine. What
Peter showed this morning......
I also think I would like to pursue that same
regulation idea, but in the LV primary, as you have suggested.
Have you ever seen a spec on the windings
ratio(s) of the HV transformer for Vic/Lionel/Eni? (OR the
inductances, from which the ratios can be calculated?) I tried
(over 2yr ago) to measure the inductances.... worked fine on the
primary's but my instrument was not stable on the secondary....)
rogerw
On 4/7/2022 1:29 PM, Geo Dowell wrote:
Let's? skip that for now.?
Will a single series Zener, say 100V, operate if the supply
is limited to 1 uA by the load resistance?
Is there a spec for that?
We were talking about the LM431 the other day and you both
correctly pointed out it needs 1 mA to operate, but what does
a Zener need to operate, current wise, assuming there is more
than adequate V present to break it over?
From: "Roger Whatley"
<rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 12:02:38 PM
Subject: Re: [CDV700CLUB] Question and an interesting
site for those that modify CDV700s and more.
Geo,
With UnRegHV = 1300V and dropping
resistor = 1.8Meg,
No load, 910.00V
Rload = 1G, 909.99V
Rload = 100Meg, 909.86V,
Rload = 10Meg, 909.01V.
If one were to measure on the other
side of the 3.3Meg resistor going up the cable to the GM
tube, a very different result would ensue. 1G would be
very handy! But, if ne knows the numbers, one can
calculate from the loaded measurement what the infinite
input impedance
scope would have
seen
rogerw
On 4/7/2022 11:41 AM, Roger
Whatley via groups.io wrote:
good question. I will hazard a
MindSim answer, then will do the simulation.
As long? as the loading of the Zener
String regulated node does not approach to close to
the current flowing into the Zener, it will not drop
the voltage too much.
(900+V/1G) << (1300V-
900+V)/1.8Meg? , or,
0.9uA << 222uA
So, the Zener String sees a very
negligible change in current with a 1G loading at the
anode of the string, since 222uA-0.9uA ~ 221uA is
hardly any change. Even if you loaded it down to only
10uA in the Zener string you would not see a lot of
change, as it depends on the regulation curve.
(By gosh! you just told me how I can
measure the regulation curve over voltage with a fixed
HV supply! Wallah!)
So, continuing Stream of
Thought..... the more interesting case is not UnRegHV
= 1300V but what if only 1000v? Then,
0.9uA << (1000V-900V)/1.8Meg?
,or,
0.9uA << 55.5uA
Still lots of room to load it and
leave 10uA or more for the Zener String.
I actually think (I think, I am not
sure) that the typical HV Generator is going to be
current limited by the time it gets to maybe 20uA at
some UnRegHV voltage well below the OpenCircuit
voltage....... in that case:
0.9uA << 20uA (or whatever the
current-limited number is. When I designed the Lionel
and Vic HV Generators for lower power consumption, I
shot for a 10uA output current.)
rogerw
On 4/7/2022 11:05 AM, Geo
Dowell wrote:
I don't know, never saw that listed either.
Meantime do this simple sim for me.
+1300V DC to cathode of a Zener ( can be via?
1.8M Ohm res. or direct in this case only). Any
Zener. On the other side of the Zener, a 1000 M Ohm
load to ground(-).
What V does the infinite impedance scope probe
show at the junction of anode and 1G load?
I am not good with simulators, but physically do
this on the workbench every day.
Geo
From: "Roger Whatley" <rogwhat53@...>
To: "CDV700CLUB" <[email protected]>
Sent: Thursday, April 7, 2022 10:46:43 AM
Subject: Re: [CDV700CLUB] Question and an
interesting site for those that modify CDV700s and
more.
Geo,
Ok, I got a bit
curious...... If a Zener String of 900+V can
change +/-40V over -25degC to +75degC, what
did the original Corotrons do?
IE, a Victoreen GV3A
Corotron?
It turns out that this Vic
catalog does not give a spec on the basic GV3A
used, but does give temp info on the "High
Temperature" version:
?
page 15
So, you can see an original
900V High Temp Corotron only varied 16V from
-65degC to 150degC...... pretty impressive I
think.
We are replacing these
things with Zener Strings with relatively high
positive tempco......
I think the ultimate
economic answer is to regulate in the primary
circuit, just as you suggested, and as ENi
did, and depend on the fixed transformer
secondary ratio to get the regulated HV, and
to temperature compensate the primary along
with an adjustable trim capability.
rogerw
On 4/7/2022 9:58 AM,
Roger Whatley via groups.io wrote:
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.
--
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.
|
