which diode for 55 Khz switching supply??

[Albert]

Later today perhaps, I need to get some work done too! My last serious use
of spice was modeling all 14 boards in a weather satellite! Found many
interesting things in the circuits that no one expected!

I'm a spice newbee, got off to a bad start in spice by starting out
with crippleware though. I'm glad I didn't pay real money for the
program I started out with! I lost alot of time tho, because I
invested the time to learn how to run the crippleware! I shoulda just
started out with LTSpice in the first place!

Good luck to all.

A

 

[John Larkin]

WW2 vintage sniperscopes used a Zamboni pile, a series arrangement of
copper-zinc primary cells.

as I recall....

Bill

There was one version that used a watch-spring clockwork thing to make
a roughly 1 pps, 50 msec contact closure (rough numbers from memory.)
That drove a stepup transformer in flyback mode, into a tiny
cold-cathode rectifier tube. Pretty cool for 1945-era switching
supplies.

I've seen Russian night-vision units that used a pushbutton as the
switch between the battery and the transformer primary. As the HV caps
discharge and the image gets dim, you sort of pump it manually until
it's bright enough.

John

 

[Jim Adney]

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.

Do they also have a C-W with 10 or more stages?

While the current required to actually drive the PM tube is quite
small, the lower stages also have to carry all the current drawn by
the stray capacitances. At 55 kHz this becomes significant unless the
mechanical design is very carefully done. There is also the power loss
due to all the reverse recovery current in each of the diodes. I would
expect all of these currents, with the P-N voltage drop across each
diode, to eventually add up to more than 1/3 W.

If you could do with fewer than 10 stages it would be better, but his
PM tube needs all 10 stages.

-

 

[Albert]

While the current required to actually drive the PM tube is quite
small, the lower stages also have to carry all the current drawn by
the stray capacitances. At 55 kHz this becomes significant unless the
mechanical design is very carefully done. There is also the power loss
due to all the reverse recovery current in each of the diodes. I would
expect all of these currents, with the P-N voltage drop across each
diode, to eventually add up to more than 1/3 W.

If you could do with fewer than 10 stages it would be better, but his
PM tube needs all 10 stages.

I'm not sure the bias voltage sees the interelectrode capacitance
because it is pure (almost) dc, once the input to that dynode is
charged, it stays charged, it's dc.

Even so, the actual C can't be more than a pf, and that cap is in
paralell with .1-.3 uF cap in the cw stage for that dynode. I just
can't imagine the losses being large::>

I would think the trr losses would be the major losses.

Forward voltage drop is probably around 20v (total), but that's fairly
small compared tp 1 kV.

For reference, the Big H's HC120 and HC123 120 Khz cw draw 7-8 ma from
a 14 v supply when the tube does not see light input.

I have never seen a Spice model for a pm tube, but I do have a nice
book about them. I'll give it a once over tomorrow.

Smile....

A

 

[John Larkin]

I would think the trr losses would be the major losses.

If you drive a C-W with a square wave, or at least wide pulses, diode
reverse recovery won't matter much. If charging current spikes taper
off to basicly zero before the drive reverses, diode carriers will
recombine by themselves in some few microseconds. So keep the drive
squarish and low frequency for max efficiency. Umm, a piezo can't do
this.

John

 

[Mark Jones]

In news:[email protected] (John Larkin):

If you drive a C-W with a square wave, or at least wide pulses, diode
reverse recovery won't matter much. If charging current spikes taper
off to basicly zero before the drive reverses, diode carriers will
recombine by themselves in some few microseconds. So keep the drive
squarish and low frequency for max efficiency. Umm, a piezo can't do
this.

John

IIRC, the tube just needs the specified DC voltages and currents present at
each leg of the tube, right? Maybe I'm way out of my league here, but what
do we think about DC --> 10KHz chopper --> step-up transformer -->
multi-tapped toroidal step-up transformer --> leg to each division voltage?
Just tap off the toroid at the appropriate number of secondary turns, add a
HV diode and smoothing cap for each and be done with it. Not as simple as a
resistor string, but might dissipate less power? Of course this assumes a
common ground, and might swing all over the place when first fired up...
sorry just throwing out ideas.

 

[John Woodgate]

I read in sci.electronics.design that ctsbillc <[email protected]>

WW2 vintage sniperscopes used a Zamboni pile, a series arrangement of
copper-zinc primary cells.

as I recall....

Yes. A Zamboni pile consists of a series of layers of three discs -
copper-paper-zinc. I'm not quite sure what the paper is impregnated
with, but it's probably ammonium chloride. No depolarizer is present,
because the current is so low the hydrogen has time to leak away.

There may be 1000 layers or more.

 

[John Woodgate]

step-up
transformer --> multi-tapped toroidal step-up transformer -->

These add cost, size and weight, especially the latter.

 

[Albert]

If you drive a C-W with a square wave, or at least wide pulses, diode
reverse recovery won't matter much. If charging current spikes taper
off to basicly zero before the drive reverses, diode carriers will
recombine by themselves in some few microseconds. So keep the drive
squarish and low frequency for max efficiency. Umm, a piezo can't do
this.

John

I have looked at this to some degree. To do a squarewave (chopped dc)
you need fast edges, this takes alot of power at each transition.
Because the edges are square, you need much higher frequency
capability diodes in order to handle the high frequency components of
the squarewave. The trr would make the diodes much more lossy (I
think).

I actually have a diagram of a switching setup for 100v dc which Win
gave to me. I've modeled it and tweeked it. It has a problem with the
tranasitors conducting at the same time for a short period of time,
which results in alot of power being wasted. It might be possible to
remedy this by further mods, but I haven't worked on this.

In any event, I can't see major benefits as the result of going to a
squarewave input to the cw.

The Hamamatsu implementations use a very pure sine wave, a class ab
linear power oscillator. Again, that's not to say that squarewaves
won't work<<:

A

 

[Albert]

In (John Larkin):


IIRC, the tube just needs the specified DC voltages and currents present at
each leg of the tube, right? Maybe I'm way out of my league here, but what
do we think about DC --> 10KHz chopper --> step-up transformer -->
multi-tapped toroidal step-up transformer --> leg to each division voltage?
Just tap off the toroid at the appropriate number of secondary turns, add a
HV diode and smoothing cap for each and be done with it. Not as simple as a
resistor string, but might dissipate less power? Of course this assumes a
common ground, and might swing all over the place when first fired up...
sorry just throwing out ideas.

Good to have some new blood in the discussion Mark! Thanks for the
comment.

It has promise, but I think there are problems....

Ultra miniature transformers have standby power problems. When the
actual power needed by the tube is so small, any standby power wasted
in a linear transformer amounts to a major loss. I did have a
discussion with Pico Transformers Inc. several years back, and there
is no way around this. If you apply ac to the input of a transformer
with a very light load on the secondary, the transformer primary
itself is gonna draw alot of current due to lack of impedance in the
primary. You can add more turns to make a higher impedance, but then
you loose it all when you look at the losses in the secondary due to
reflected reactance of the secondary (which is the SQUARE of the step
up ratio). This looks like a shunt inductance and gets to be a major
problem with large primary inductance.

There is another problem too.... The 1st stage draws about 100 ua, the
top dynode draws fA. A transformer is going to have problems supplying
even steps of output voltage because there is a one million times
ratio between the current the different windings supply. Your nice 100
volt steps might be 100v, 103v, 106v, 110v, 120v, 140v, 170v, 200v
etc.

If you really put 200 volt differential voltage on the upper dynodes,
the tube arcs- between the upper dynodes.

Can you see anyway around these problems??

A

 

[John Woodgate]

If you apply ac to the input of a transformer with a very
light load on the secondary, the transformer primary itself is gonna
draw alot of current due to lack of impedance in the primary.

No 'lack of impedance' if it's properly designed, and the secondary load
is irrelevant.

You can
add more turns to make a higher impedance, but then you loose it all
when you look at the losses in the secondary due to reflected reactance
of the secondary (which is the SQUARE of the step up ratio). This looks
like a shunt inductance and gets to be a major problem with large
primary inductance.

No, this is all way off-beam. It's not even wrong!

There is another problem too.... The 1st stage draws about 100 ua, the
top dynode draws fA. A transformer is going to have problems supplying
even steps of output voltage because there is a one million times ratio
between the current the different windings supply. Your nice 100 volt
steps might be 100v, 103v, 106v, 110v, 120v, 140v, 170v, 200v etc.

You wouldn't be able to make a transformer that had such high source
impedances that would lose you 97 V at 100 uA, and if the no-load
voltage is 100 V, it wouldn't go UP with a very light load.

If you really put 200 volt differential voltage on the upper dynodes,
the tube arcs- between the upper dynodes.

Can you see anyway around these problems??

Either someone fed you with a load of nonsense about transformers or you
didn't hear clearly. There are problems with transformers in this
application, but those you envisage don't exist.

 

[Roger Gt]

I'm a spice newbee, got off to a bad start in spice by starting out
with crippleware though. I'm glad I didn't pay real money for the
program I started out with! I lost alot of time tho, because I
invested the time to learn how to run the crippleware! I shoulda just
started out with LTSpice in the first place!

Good luck to all.

A

Well. given the load you stated, and setting resistors on the first five
outputs to simulate that load. With a Square wave 50% duty cycle, 102V
55Khz, the outputs were 100.6 volts per step. To 1.066KV Note. Due to the
loads variation from the low end.
The first four stages used 200nF caps, the rest (6) used 100nF caps. All
200V
I also switched to MA158 diodes. 200V, 100Ma, 1uA leakage.
The larger diodes work, but require more drive.
Input power in this form was about 1/2 watt.
Not as efficient as you were hoping for.

 

[John Woodgate]

Well. given the load you stated, and setting resistors on the first
five outputs to simulate that load. With a Square wave 50% duty cycle,
102V 55Khz, the outputs were 100.6 volts per step. To 1.066KV Note.
Due to the loads variation from the low end. The first four stages used
200nF caps, the rest (6) used 100nF caps. All 200V I also switched to
MA158 diodes. 200V, 100Ma, 1uA leakage.
The larger diodes work, but require more drive.
Input power in this form was about 1/2 watt.
Not as efficient as you were hoping for.

How dismally objective. Sloman Award, Class 3.

Would have been class 2 if you hadn't written 'KV' and 'Ma'.(;-)

 

[Roger Gt]

"John Woodgate" wrote in message

Roger Gt wrote

How dismally objective. Sloman Award, Class 3.

Would have been class 2 if you hadn't written 'KV' and 'Ma'.(;-)
--

If I cared, I would ask --
This from someone who drives on the wrong side of the road?
What the HELL is a "Sloman Award"? or are you (as Usual) just joking?

 

[John Woodgate]

"John Woodgate" wrote in message


If I cared, I would ask --
This from someone who drives on the wrong side of the road?

Only at Savoy Place.

 

[Roger Gt]

<Albert> wrote in message
Well. given the load you stated, and setting resistors on the first five
outputs to simulate that load. With a Square wave 50% duty cycle, 102V
55Khz, the outputs were 100.6 volts per step. To 1.066KV Note. Due to the
loads variation from the low end.
The first four stages used 200nF caps, the rest (6) used 100nF caps. All
200V
I also switched to MA158 diodes. 200V, 100Ma, 1uA leakage.
The larger diodes work, but require more drive.
Input power in this form was about 1/2 watt.
Not as efficient as you were hoping for.

Revisited during lunch, I tried a Sine wave input. 37V at 55Khz. Input
current was only 12mA average. Much better! About the same voltages out.

 

[Roger Gt]

"Plonk" 30 days!

 

[Roger Gt]

"Roger Gt" wrote in message

Revisited during lunch, I tried a Sine wave input. 37V at 55Khz. Input
current was only 12mA average. Much better! About the same voltages out.

..44 watts isn't bad! May be able to improve on it with time to play with
the values.

Also... I do not have the spice model for it, but a diode array MMBD2004S
looks a good choice and will cut the number of Diode packages in half.
I presume you have selected suitable capacitors, But I will list what I have
been using.... JIK

Top Magnetic

HVC0805Y5V104M200NT
HVC1206Y5V104M200NT

I prefer the 1206 for high voltage operation, but it's you pick so I
included both.
They also have 500, 1kV, and higher.

Contact information
TOP MAGNETICS CORPORATION

13925 Magnolia Avenue, Chino, California 91710

Tel: 909-590-8550 Fax: 909-590-8762

Website: www.topmagnetics.com Email: [email protected]

 

[Rene Tschaggelar]

Hmmm, battery powered ...
I'd have to think about that one.

I lost the name of the circuit. A fixed cascade of capacitors, the
lowest one on GND, Another cascade of capacitors, this time the lowest
one connected to a pushpull driver, plus a bunch of diodes zig-zag
between the two cascades make a chargepump with all elements of the
same specifications. In order to conserve energy, the pushpull needn't
to be working all the time, but only as much as to replenish the lost
charge.


Rene

 

[Jim Adney]

I'm not sure the bias voltage sees the interelectrode capacitance
because it is pure (almost) dc, once the input to that dynode is
charged, it stays charged, it's dc.

You're right, that the output points are almost static in this
situation, but in every C-W there are 1 or 2 chains of caps which run
all the way to the top of the stack which have the full voltage swing
100% of the time. It is the capacitance between these chains and the
outside world AND the static, DC, part of the stack which causes the
parasitic current draw.

Even so, the actual C can't be more than a pf, and that cap is in
paralell with .1-.3 uF cap in the cw stage for that dynode. I just
can't imagine the losses being large::>

Perhaps you're right, or maybe not. I'm really not too sure. I'm not
used to working at voltages or power levels this low, so my gut
feelings are a bit confused.

I would think the trr losses would be the major losses.

Could be. Too bad we can't buy 200V Shottkys.

-