Medium voltage (~800v) SMPS

[logjam]

Oh, color of a different horse.

600uA @ 8KV is a lot easier than umpteen mils @ 80KV.
Not i purposely mis-read your "80KV" in that list...

At that point I misunderstood how the cascade doublers worked. I
guess I really wasn't done with Verizon math. ; ) The new secondary
is about 5kV.

That load is no problem.

600uA at 80,000V is the final goal. ~40W

In the beginning I was adding a few mils here and there since I might
get a 7mA tube, forgetting how much 1mA at 80kV is. ; ) The goal of
600uA is so that hopefully I can end up with at least a functional
500uA.

It has been a bumpy ride these first few days, but I am a fast
learner. Getting ready to try out the SPICE program.

 

[Robert Baer]

At that point I misunderstood how the cascade doublers worked. I
guess I really wasn't done with Verizon math. ; ) The new secondary
is about 5kV.




600uA at 80,000V is the final goal. ~40W

In the beginning I was adding a few mils here and there since I might
get a 7mA tube, forgetting how much 1mA at 80kV is. ; ) The goal of
600uA is so that hopefully I can end up with at least a functional
500uA.

It has been a bumpy ride these first few days, but I am a fast
learner. Getting ready to try out the SPICE program.

Well, you should now be aware of a few probelms with the transformer:
1) lots of leakage inductance, as you cannot interwind so many output
turns to so few input turns.
2) Lots of capacitance to drive, as the inter-winding capacitance of the
secondary is going to severely reflect back to the primary.
After all, a 5KV secondary is going to have a *lot* of turns.
Be careful with insulation, you will need some between the secondary
and the coer itself.
Have you picked a core and determined volts per turn for a "final"
prototype?

 

[logjam]

Well, you should now be aware of a few probelms with the transformer:

1) lots of leakage inductance, as you cannot interwind so many output
turns to so few input turns.
2) Lots of capacitance to drive, as the inter-winding capacitance of the
secondary is going to severely reflect back to the primary.
After all, a 5KV secondary is going to have a *lot* of turns.
Be careful with insulation, you will need some between the secondary
and the coer itself.
Have you picked a core and determined volts per turn for a "final"
prototype?

I still haven't come up with a way to find the ultimate minimum turns
per volt for the primary.

I've been rethinking the secondary output voltage. 10kV capacitors
are expensive but 6.3kV capacitors are more affordable. I may want to
build a 3kV secondary with more cascade sections than use larger more
expensive capacitors and fewer stages. More stages with a 3kV input
will result in less output ripple too.

I still have not made the SPICE simulation work. I need to choose a
capacitor value and fill in all of the characteristic information in.

If I use a form and a split core then will the form be the insulation
I would need?

Grant

 

[Frithiof Andreas Jensen]

have to only look to google for information. They never did explain
how the mA feedback worked.

Usually, what one does to measure HV is to feed a *current* into a buffer
amplifier.

The commercial machine with 160kV 20mA output has 10 stages. The
225kV 10mA machine has 14. This I can trust because it is in the
official maintenance manual schematics.


I was hoping for something smaller. I should be able to get at least
5,000-10,000v out of a small hand wound transformer. I've seen it
done on an x-ray machine by hand. Maybe I need special enameled wire?

Using the same ETD29 core I would need 10 primary turns and 5266
secondary turns for a 5000v secondary. I'll have to figure out
exactly how many cascade stages I want and then figure out the
transformer.

You cannot get a transformer that small to work: *if* it does not arc over,
you will loose all the power in inter-winding capacitances (before it arcs
over).

However, there is a much easier way: Use an automotive ignition transformer
in either a flyback topology (easiest) or a resonant converter (more
efficient). Ingnition transformers are cheap and available (unlike
attractive wimmen)

An typical ignition transformer should be good for about 100 W at 25 kHz and
probably give you 25 kV!! Enough to require EHT diodes (BYW 95 ??) and oil &
silicone potting for the rectifier stack. And deadly, really it is!!

 

[Robert Baer]

I still haven't come up with a way to find the ultimate minimum turns
per volt for the primary.

I've been rethinking the secondary output voltage. 10kV capacitors
are expensive but 6.3kV capacitors are more affordable. I may want to
build a 3kV secondary with more cascade sections than use larger more
expensive capacitors and fewer stages. More stages with a 3kV input
will result in less output ripple too.

I still have not made the SPICE simulation work. I need to choose a
capacitor value and fill in all of the characteristic information in.

If I use a form and a split core then will the form be the insulation
I would need?

Grant

Sorry; all else being equal, the number of stages is not related to
amount of ripple.
Try load current, stage capacitance, load capacitance for starters.