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120kv 10-20mA SMPS

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Linas

Sat Aug 20 2011, 07:28PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

I will give another shot for this transformer. I found guy who winds HV transformers, witch is filled with epoxy compound and lot of insulation.
so i have 4cm for insulation from both sides, and will need at least 2cm from core, and everything will be filled with epoxy (13kv/mm breakdown)
also secondary will be insulated from ferrite core, so first turns don't want so badly brake insulation in between core and secondary.

Adam Munich

Sat Aug 20 2011, 07:31PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

How about an E core, with the primary in the center and the out of phase secondaries on the 'legs'?.

It'd give you +60kV and -60kV, but still it'd be a 120kV difference (and it'd make for a more reliable transformer)

Linas

Sat Aug 20 2011, 07:37PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

problem is that i also will need to make circuit with 65KV insulation for filament, and that will consume space
and i just have U shape core with 12cm winding space

Adam Munich

Sat Aug 20 2011, 07:41PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well then, insulation from the core will not be needed with a single ended supply; just ground one side of the secondary to the core.

Come to think of it, core insulation is not needed with a double ended supply either.

Linas

Sat Aug 20 2011, 07:59PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

Grenadier wrote ...

Well then, insulation from the core will not be needed with a single ended supply; just ground one side of the secondary to the core.

Come to think of it, core insulation is not needed with a double ended supply either.

i will use half bridge to drive it.
so i will have time for 0V to core, and other half period whole 120KV in between (since is not flyback topology)
any idea about plexy glass breakdown voltage ?
right now making cdr file for laser cutter for carcase of secondary and primary

Adam Munich

Sat Aug 20 2011, 08:09PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't understand... if your reference point is the core, and one end of the secondary is connected to that point... at one half cycle the HV out will be +, the other half cycle - relative to the core.

MOTs, NSTs, XRTs, and even some flybacks ground their cores. Unless you plan on putting another one of these transformers in series, grounding the core is the wisest thing to do.

Linas

Sat Aug 20 2011, 08:35PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

i will keep core as it is. because if i ground it, i will definitely have 120Kv voltages differences.
idea now that my secondary will have same 100KV insulation from core, that should minimize breakdown chance between secondary start and core, also because core will be floating, secondary end also will not be so attracted to strike to core.
but that theory purely for DC
capacitance will give for core some voltage, but i have no idea how it will react and what value will be during peak in secondary
maybe is good idea connect core to middle of secondary, that way, i will have just 65KV differences in all windings
hell, i don't know much about this stuff.
i am open for ideas

Adam Munich

Sat Aug 20 2011, 10:27PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I'd go for the center tapped transformer. That way you'd only need to insulate 65kV, which is a hell of a lot easier than 120kV

Linas

Sun Aug 21 2011, 08:37AM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

last day, i was talking with my friend, and come up with two potential designs:
First: i should make 65KV transformer with grounded start to core (optional) and make 2x multiplier on output. and secondary will be winded as triangle. ( so if i have 120KV and caps are 1nF 80KV, Vdrop @ 20mA ? (50KHz)
Second: make 120KV secondary with triangle shape windings, ground start, and use single diode ( simple flyback)
So if i sue that, and 666pF 120kv on output, with 20mA load Vripple ??

hm, i made calculation by using HV.wiki formula.(65KV transformer +2x multiplier)
so if my transformer is ideal , also i have ideal caps, and diodes ( more or less) i get just 400Vdrop ?
$8514b157f6c0e5660c803fe6a98091f8$
C is 1nF (80KV) f=50Khz, I=20mA, N=1 ( since i have 2 caps, so N=caps/2)

so is it possible ? because it sound to good to be truth ( and also i have BYV26E diodes for this task )

jpsmith123

Tue Aug 23 2011, 02:18AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Hello Linas, here's the result of a spice simulation of your circuit:

I think it will be very difficult if not impossible to get 65 kv (peak) out of a "typical" ferrite transformer. You will run into problems with parasitic capacitance and/or capacitive coupling to the core, and insulation problems.

I think you'll probably have to go with a significantly lower transformer voltage and a correspondingly bigger multiplier.

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