which diode for 55 Khz switching supply??

[albert]

Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

Al

 

[John Larkin]

On Fri, 12 Dec 2003 10:10:21 -0500, albert <> wrote:

Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

Al

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John

 

[Mark Jones]

In news:73qjtvg2gi6374lcngid4i6m8aukmfi59p@4ax.com (John Larkin):

On Fri, 12 Dec 2003 10:10:21 -0500, albert <> wrote:

Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

Al

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John

Also you'll probably find that there will be other losses like diode drop,
ESR, parasitic inductance, etc. Plan on over-driving the input to some
degree to get the required output. If you need a form of regulation, you
could create a low-current resistor divider on the output, fed to an op-amp,
which adjusts the input voltage... that said, it would probably be more
effecient if you could reduce the number of multiplier stages as much as
possible. Even in HV flyback supplies, typically only one or two multipliers
are used; the input voltage is typically ~9000v.

Mark

 

[albert]

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John


Also you'll probably find that there will be other losses like diode drop,
ESR, parasitic inductance, etc. Plan on over-driving the input to some
degree to get the required output. If you need a form of regulation, you
could create a low-current resistor divider on the output, fed to an op-amp,
which adjusts the input voltage... that said, it would probably be more
effecient if you could reduce the number of multiplier stages as much as
possible. Even in HV flyback supplies, typically only one or two multipliers
are used; the input voltage is typically ~9000v.

John and Mark, Thanks!

It's for a photomultiplier supply, so it needs to have 10 stages. Each
stage connects to a dynode element, so there is no way around the
necessity of having many stages. The good news is that the upper
stages draw pico amps (or less) and the lower voltage stages supply
the brunt of the current.

I recently discovered that many have problems with the concept of
drawing power from each stage-they generally think of a a voltage
multiplier as a means to achieve a single (but very high) output
voltage.

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.

Thanks again,

Al

 

[John Stewart]

albert wrote:

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John


Also you'll probably find that there will be other losses like diode drop,
ESR, parasitic inductance, etc. Plan on over-driving the input to some
degree to get the required output. If you need a form of regulation, you
could create a low-current resistor divider on the output, fed to an op-amp,
which adjusts the input voltage... that said, it would probably be more
effecient if you could reduce the number of multiplier stages as much as
possible. Even in HV flyback supplies, typically only one or two multipliers
are used; the input voltage is typically ~9000v.


John and Mark, Thanks!

It's for a photomultiplier supply, so it needs to have 10 stages. Each
stage connects to a dynode element, so there is no way around the
necessity of having many stages. The good news is that the upper
stages draw pico amps (or less) and the lower voltage stages supply
the brunt of the current.

I recently discovered that many have problems with the concept of
drawing power from each stage-they generally think of a a voltage
multiplier as a means to achieve a single (but very high) output
voltage.

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.

Thanks again,

Al

You will need very good regulation of the voltage. Gain of any PM
I ever worked with was a very steep function of the operating voltage.

Good Luck, John Stewart

 

[albert]

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.



You will need very good regulation of the voltage. Gain of any PM
I ever worked with was a very steep function of the operating voltage.

Good Luck, John Stewart

I might need the luck, thanks for your good wishes.

I know about the regulation requirements, would like to spice model
the pm tube I intend to use with the power supply, but I think I can
use multiple ramping current sources to do the job in spice.

Regards,

Al

 

[Oppie]

when I worked with PMTs, we always had a regulated HV supply which drove the
dynode chain resistors. One good technique was to put a 100V zener in place
of the resistor between the photocathode and the first dynode. this forces a
high fixed gain from the first stage (so you don't just multiply noise).
Also, the dynode chain resistors were chosen such that the voltages didn't
re-distribute too much as the anode current rises. Otherwise it causes
linearity problems. In general, gain is proportional (almost exponential) to
the voltage between dynodes. Too low a voltage and the tube saturates. Too
high and the noise increases.

Also a shutdown provision for the high voltage upon sensing an abnormally
high photocurrent is a good idea to protect an expensive tube.

Back to the original question, I have a 5kv rated unit I use from EDI
(electronic Devices Inc) #DR500 and another one from HV Components #G5FS.
Both companies make lower voltage units.

Oppie
http://www.e-edi.com/
http://www.electronicdevices.com/

--
For correct response address, remove -nospam-
=========
<albert> wrote in message news:ggvjtv4rbsjri4c2ecredupsiajbpvhgmb@4ax.com...

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.



You will need very good regulation of the voltage. Gain of any PM
I ever worked with was a very steep function of the operating voltage.

Good Luck, John Stewart


I might need the luck, thanks for your good wishes.

I know about the regulation requirements, would like to spice model
the pm tube I intend to use with the power supply, but I think I can
use multiple ramping current sources to do the job in spice.

Regards,

Al

 

[Asimov]

"albert" bravely wrote to "All" (12 Dec 03 10:10:21)
--- on the heady topic of "which diode for 55 Khz switching supply??"

Use a Whilmhurst generator and you won't need to multiply anything.
All kidding aside for 55KHz and 100uA, I think a simple switching diode
would suffice as long as the voltage rating agrees. I think something
like a higher voltage rated version of a 1N4148 would be okay. Just shop
in a diode catalog to find one suitable for over 200 volts. Perhaps a
fast recovery 1 ampere diode might work in a pinch. A couple of hundred
volts is nothing for those often rated at 600 volts and more.

al> From: albert <>
al> Good Day All.

al> I am building a cockcroft-walton voltage multiplier. It will have 10
al> stages, with each stage having a 100 volt output, so the total output
al> is ~1000 volts. It will operate at 55 Khz and only needs to produce
al> small currents (microamps). I want to have minimal switching diode
al> losses since I will have lots of diodes:>:

al> I need a fast diode with small input capacitance. I need to have it
al> withstand 200 volts at 100 microamps.

al> Which diode should I use??????

al> All suggestions are appreciated.

al> Al

al> -!- Internet Rex 2.29
al> ! Origin: Posted via Supernews, http://www.supernews.com (1:167/133.1)



.... # <--- electrocuted tribble

 

[Watson A.Name - "Watt Sun]

In article <ufsjtvsrk608deu0rqj0p8s6stgk61707u@4ax.com>, albert <>
mentioned...

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John


Also you'll probably find that there will be other losses like diode drop,
ESR, parasitic inductance, etc. Plan on over-driving the input to some
degree to get the required output. If you need a form of regulation, you
could create a low-current resistor divider on the output, fed to an op-amp,
which adjusts the input voltage... that said, it would probably be more
effecient if you could reduce the number of multiplier stages as much as
possible. Even in HV flyback supplies, typically only one or two multipliers
are used; the input voltage is typically ~9000v.



John and Mark, Thanks!

It's for a photomultiplier supply, so it needs to have 10 stages. Each
stage connects to a dynode element, so there is no way around the
necessity of having many stages. The good news is that the upper
stages draw pico amps (or less) and the lower voltage stages supply
the brunt of the current.

I recently discovered that many have problems with the concept of
drawing power from each stage-they generally think of a a voltage
multiplier as a means to achieve a single (but very high) output
voltage.

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.

The PMTs I've seen use a resistive divider, not a C-W V multiplier.
There's nothing wrong with using a resistive divider, after all, you
said that it only needs picoamps.

The 1N4148 signal diode series seems to have one that's rated for a
couple hundred volts, it's the 1N4155.

The 1N4005 series will have too much losses at 55 kHz. You should
consider using regular 60 or 50 Hz; with that low a current the caps
would be reasonably small and you could use 1N4005 rectifiers.

Thanks again,

Al

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[albert]

The PMTs I've seen use a resistive divider, not a C-W V multiplier.
There's nothing wrong with using a resistive divider, after all, you
said that it only needs picoamps.

While the tube draws picoamps at the upper dynodes, the resisitive
divider is a constant load on the power supply...regardless of the
current drawn by the tube itslef.

If you think this is OK, well, I suppose we have different
standards::> But, typical values for the divider resistor are 330K
(each), in series this is (about) 3.3 meg ohms (assuming 10 resistors
are needed for the divider string). This 3.3 meg total resistance
appears across the 1KV supply whether the tube is conducting or not.
In fact, you can take the tube away completely and those resistors
still load the power supply and dissipate the same amount of heat into
the air.

Resistive dividers dissipate big amounts of heat and are cheap. In
some aps, they are clearly the way to go.

For battery powered portable operation the cockcroft-walton is the way
to go.

You see resistive dividers because your aps aren't don't need a high
efficiency power supply and becasue your aps can tollerate the heating
from the dissipation of the resistors.

The 1N4148 signal diode series seems to have one that's rated for a
couple hundred volts, it's the 1N4155.

The 1N4005 series will have too much losses at 55 kHz. You should
consider using regular 60 or 50 Hz; with that low a current the caps
would be reasonably small and you could use 1N4005 rectifiers.

I had found the 4148, they are cheap and available. They might be ok.
There is also the 1N3060, used by Hamamatsu and others...it's more
expensive and less 'available' tho.

I did some in depth researching yesterday. Some higher voltage diodes
have high leakage (which is devastating for the upper dynodes
efficiency when driven from a CW supply. Still others have 1.25 volt
forward drop...which adds up when you have 22 of them in a CW
multiplier! Clearly, (as one of you pointed out earlier) there is no
easy answer and there must be a compromise in the selection process.


Regards,

Al

 

[Asimov]

"Watson A.Name - Watt Sun, Dark Remo" bravely wrote to "All" (13 Dec 03
00:36:45)
--- on the heady topic of "Re: which diode for 55 Khz switching supply??"

WA-W> From: Watson A.Name - "Watt Sun, Dark Remover"
WA-W> <alondra101@hotmail.com> Subject: Re: which diode for 55 Khz switching
WA-W> supply?? Organization: Brighter Than Bright
WA-W> Xref: aeinews alt.binaries.schematics.electronic:6196
WA-W> sci.electronics.repair:14638 sci.electronics.equipment:2041
WA-W> sci.electronics.misc:7958 sci.electronics.design:27752
WA-W> sci.electronics.components:4299
WA-W> In article <ufsjtvsrk608deu0rqj0p8s6stgk61707u@4ax.com>, albert <>
WA-W> mentioned...

Take a look at MMBD2004, aka Central CMPD2004S. Dual 250 (or 300) volt
diode in a SOT-23. Central also has a triple HV diode in a tiny
package.

John


Also you'll probably find that there will be other losses like diode drop,
ESR, parasitic inductance, etc. Plan on over-driving the input to some
degree to get the required output. If you need a form of regulation, you
could create a low-current resistor divider on the output, fed to an op-amp,
which adjusts the input voltage... that said, it would probably be more
effecient if you could reduce the number of multiplier stages as much as
possible. Even in HV flyback supplies, typically only one or two multipliers
are used; the input voltage is typically ~9000v.



John and Mark, Thanks!

It's for a photomultiplier supply, so it needs to have 10 stages. Each
stage connects to a dynode element, so there is no way around the
necessity of having many stages. The good news is that the upper
stages draw pico amps (or less) and the lower voltage stages supply
the brunt of the current.

I recently discovered that many have problems with the concept of
drawing power from each stage-they generally think of a a voltage
multiplier as a means to achieve a single (but very high) output
voltage.

If I go diode hunting, what should I look for in the spec sheets? Many
have a Trr (reverse recovery time) and it's also common for them to
spec the capacitance of the junction.

WA-W> The PMTs I've seen use a resistive divider, not a C-W V multiplier.
WA-W> There's nothing wrong with using a resistive divider, after all, you
WA-W> said that it only needs picoamps.

WA-W> The 1N4148 signal diode series seems to have one that's rated for a
WA-W> couple hundred volts, it's the 1N4155.

WA-W> The 1N4005 series will have too much losses at 55 kHz. You should
WA-W> consider using regular 60 or 50 Hz; with that low a current the caps
WA-W> would be reasonably small and you could use 1N4005 rectifiers.

The inconvenience is that with 50/60 Hz the capacitors will need to be
much larger to deliver a decent amount of current. Also it would seem
that the application would probably benefit from being portable using
battery power. I suspect the original poster is trying to design a
school project prank zapper.

.... KPLA: Klingon Radio: All Klingon Opera, All The Time.

 

[Jim Adney]

On Sat, 13 Dec 2003 10:12:53 -0500 albert <> wrote:

If you think this is OK, well, I suppose we have different
standards::> But, typical values for the divider resistor are 330K
(each), in series this is (about) 3.3 meg ohms (assuming 10 resistors
are needed for the divider string). This 3.3 meg total resistance
appears across the 1KV supply whether the tube is conducting or not.
In fact, you can take the tube away completely and those resistors
still load the power supply and dissipate the same amount of heat into
the air.

The 3.3 MOhm across 1000 volts disipates ~1/3 Watt. If you think that
your losses with a 55 kHz, 10 stage C-W will be less, then you must
never have tried it before.

Resistive dividers dissipate big amounts of heat and are cheap. In
some aps, they are clearly the way to go.

In general I agree with you. I just don't think your instincts were in
the right direction this time.


-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

 

[John Larkin]

On Sun, 14 Dec 2003 10:25:00 -0600, Jim Adney <jadney@vwtype3.org>
wrote:

The 3.3 MOhm across 1000 volts disipates ~1/3 Watt. If you think that
your losses with a 55 kHz, 10 stage C-W will be less, then you must
never have tried it before.

If done right, the C-W losses will be much less than 1/3 w, and
provide lower dynode impedances too. Night-vision gear uses HV
supplies that have amazingly low idle currents. WWII-vintage
sniperscope supplies would run for weeks on one zinc-carbon flashlight
battery.

Resistive dividers dissipate big amounts of heat and are cheap. In
some aps, they are clearly the way to go.

A sot-23 dual diode and a couple of 2 nF surface-mount caps don't cost
much, and dissipate nil. Several companies make commercial C-W PMT
sockets, but they tend to be expensive.

John

 

[Roger Gt]

<albert> wrote in message news:memjtvk92qt46qon8rsr6i8qdscqm2andv@4ax.com...

Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

http://usa.hamamatsu.com/hcpdf/parts_HC/HC120-01.pdf

It provides 1100VDC from +/-18VDC in. Maybe it would be as easy to just
buy one?

 

[Albert]

If they made it as a building block assy, I'd think about it. The way
they currently package thier cw supplies is a severe limitation
because you can't wire it up to other tubes. I've spoken to them about
this. they told me to pound sand.

I think you should check the price before suggesting Hamamatsu::>

I've chosen to 'just say no' to the big H. Your mileage will vary, I
shall pray for you.

http://usa.hamamatsu.com/hcpdf/parts_HC/HC120-01.pdf

It provides 1100VDC from +/-18VDC in. Maybe it would be as easy to just
buy one?

 

[Roger Gt]

<Albert> wrote in message

If they made it as a building block assy, I'd think about it. The way
they currently package their cw supplies is a severe limitation
because you can't wire it up to other tubes. I've spoken to them about
this. they told me to pound sand.

I think you should check the price before suggesting Hamamatsu::

Considering the problems you seem to have, I didn't feel price was the
critical parameter. Besides all High voltage units are relatively pricey!

I've chosen to 'just say no' to the big H. Your mileage will vary, I
shall pray for you.

Okay, your call. Sorry I made any sugestion.
I was unaware this project had religious significance, I do not need (or
Want) your prayers. I was trying to help. Only a suggestion. It has been
sometime since I have done any really high voltage power supplies, I had no
where near the problems but the criteria may have been different. Took
three attempts to get the circuit to work, but my problems were insulation
leakage due to a confined space.

Recent designs were only about 200 volts and at 330Khz. No problems there
either.

http://usa.hamamatsu.com/hcpdf/parts_HC/HC120-01.pdf

It provides 1100VDC from +/-18VDC in. Maybe it would be as easy to just
buy one?

 

[Roger Gt]

<albert> wrote in message news:memjtvk92qt46qon8rsr6i8qdscqm2andv@4ax.com...

Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

OKAY:

Possible
1N4936-T DO41 Case, 1 amp rating, 15pf 400PIV (@1A 1.2V forward, since your
operating at less current, this will be somewhat less.)
DL4936-13 MELF all ratings the same.
Both will operate at 55Khz. I use them at 330Khz!

The other problems I can not address.

 

[Roger Gt]

"Roger Gt" <Xenot@pacbell.net> wrote in message
news:SveDb.71694$aY6.55025@newssvr25.news.prodigy.com...

albert> wrote in message
news:memjtvk92qt46qon8rsr6i8qdscqm2andv@4ax.com...
Good Day All.

I am building a cockcroft-walton voltage multiplier. It will have 10
stages, with each stage having a 100 volt output, so the total output
is ~1000 volts. It will operate at 55 Khz and only needs to produce
small currents (microamps). I want to have minimal switching diode
losses since I will have lots of diodes:>:

I need a fast diode with small input capacitance. I need to have it
withstand 200 volts at 100 microamps.

Which diode should I use??????

All suggestions are appreciated.

OKAY:

Possible
1N4936-T DO41 Case, 1 amp rating, 15pf 400PIV (@1A 1.2V forward, since
your
operating at less current, this will be somewhat less.)
DL4936-13 MELF all ratings the same.
Both will operate at 55Khz. I use them at 330Khz!

The other problems I can not address.

Modeling the circuit:
Using the 1N4936 with all caps equal to .33uF and a 55Khz input.
I show a rise time of 83ns and a simulated voltage of 1.154kv with a load of
10Meg ohm in ten segments.
I did not model the Capacitor losses, but at this frequency it will not be
major.
The ripple with this kind of multiplier is significant, and may require post
generation filtering.

 

[John Woodgate]

I read in sci.electronics.design that Roger Gt <Xenot@pacbell.net> wrote
(in <FVfDb.71696$tX7.206@newssvr25.news.prodigy.com&gt about 'which diode
for 55 Khz switching supply??', on Mon, 15 Dec 2003:

Using the 1N4936 with all caps equal to .33uF and a 55Khz input.

That seems to be rather a large capacitor for 55 kHz and hardly any
current. I once used 68 nF at 50 Hz.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

 

[Albert]

On Mon, 15 Dec 2003 10:46:13 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Roger Gt <Xenot@pacbell.net> wrote
(in <FVfDb.71696$tX7.206@newssvr25.news.prodigy.com&gt about 'which diode
for 55 Khz switching supply??', on Mon, 15 Dec 2003:

Using the 1N4936 with all caps equal to .33uF and a 55Khz input.

That seems to be rather a large capacitor for 55 kHz and hardly any
current. I once used 68 nF at 50 Hz.

Hi John,

OK, I know the Big H uses .15 uF in their 120 Khz sine based products.
I modeled a 5 stage cw in my old cripple ware spice, and found .1 uF
worked well at 100 Khz square wave input model.

When I had the cripple ware spice running, I had a 5 stage cw modeled
with appropriate load resistors and discovered that the I got the same
results with a 2 stage divider. I think this is because the load is
very small past the second stage, the leakage current of the diodes in
the upper stage exceeds the load current of the output current of the
upper stages and because the caps in the upper stages are not
completely discharged and recharged (as the are in the first stage). I
concluded that one could use a properly loaded 2 stage cw and get
nearly the same results as the full 10 stage circuit (in a pm tube
model only).

Regards,

A