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1
Transformer (Ferrite Core) / Re: Designing a regulated HV supply
« Last post by davekni on Today at 06:48:18 AM »
Quote
Supposedly rated to 60W.
You need 70W (1mA at 70kV), although intermittently.  Such Chinese parts are often overrated.  It may be tricky to get 70W even intermittently.

Quote
Would there be a better suited cap for this?
Yes.  They will be larger and more expensive.

Quote
Alternatively, the X-ray head I took apart for this actually has a voltage multiplier on a PCB.... I could likely repurpose that, though it's quite a few stages. I'll take some photos of it when I get home.
Unless it is damaged, an existing multiplier designed for this exact purpose is likely better than anything home-built.  Any transformer included?

2
Transformer (Ferrite Core) / Re: Designing a regulated HV supply
« Last post by Hiemal on Today at 05:37:39 AM »
https://www.aliexpress.com/item/2255800905006413.html?spm=a2g0o.order_list.0.0.21ef18021iabbS&gatewayAdapt=4itemAdapt

is the listing for the transformer. MP-2057. UY10 core material. Supposedly rated to 60W. Secondary is 9H or greater in inductance. Core can be gapped if need be!

And, yes, those are indeed the style of caps I have. Would there be a better suited cap for this? Alternatively, the X-ray head I took apart for this actually has a voltage multiplier on a PCB.... I could likely repurpose that, though it's quite a few stages. I'll take some photos of it when I get home.
3
Transformer (Ferrite Core) / Re: Designing a regulated HV supply
« Last post by davekni on Today at 05:00:02 AM »
Quote
They're the standard blue ceramic HV caps; they're fairly chunky ones, if I remember right. Either 10 nF or 100 nF, rated to 20kV. or 30kV. I know, it's dumb that I don't remember precisely but I'll try to take a look at them when I get back home tonight.
Are they something like this example:
https://www.ebay.com/itm/393028082633
If so, their capacitance will likely drop by 10x (to 10% of spec'ed value) at full rated voltage.  They may still be useful for your needs.  The capacitance reduction needs to be taken into account in design.  Also, these caps have high loss (dissipation factor).  I've used such in a HV multiplier.  The bottom ones died due to overheating when driven at 30kHz.

Thank you for the other answers.  Also, do you have any specifications for your transformer?  Is the core gapped?  Volt-second rating, or inductance and voltage and frequency, or DC current capability?
4
Quote
Hmm, this one is trickier to achieve while ensuring zero current switching. It's easy enough with another flipflop, but I'd like to avoid that if possible as I'm already worried about board space, so I'll see if I can find something neater.
Yes, I believe your goals require separate FFs, one for synchronizing OCD and another for synchronizing interrupt input.  The OCD input also needs something to hold the compare event from current peak until next rising current edge.  That could be handled with an R/C/D circuit or R/C/transistor, or with a set/reset FF made of two gates.  If this is smaller than a new FF package, might be useful.

BTW, I cannot think of any reason the two different UCC driver chips need to have matched input delays.  Thus the two extra AHC86 sections can be made available for other uses.

Edit:  I think logic size can be reduced by replacing both the AHC08 and AHC86 with an AHC157 chip.  Also allows using a single-output comparitor, since comparitor drives select line.  I'd recommend TLV3501 as a fast comparitor with rail-to-rail IO.  That is what I use.  Input circuitry can be simplified slightly given symmetric I/O ranges.

AHC157 outputs drive the four UCC inputs.  Interrupt after FF synchronization feeds AHC157 enable input.  Each of the AHC157 input pairs are one-high and one-low.  Lower set switch based on synchronized OCD (wire to Q and Qn of OCD FF, or perhaps one output and inverter to make phase-inversion easier).  Phase inversion could be done instead by inverting CT input wires or by adding a selectable inverter stage to comparitor output.

One more note:  In freewheeling mode, the half-bridge driven by lower UCC chip will be using its diodes and not IGBTs.  Upper half-bridge will continue using IGBTs as it does between freewheeling times.  If you want to spread out power dissipation to all four diodes and IGBTs evenly, then OCD inversion needs to alternate between driver chips.  Can't think of any way to do this without adding yet another FF package.  Perhaps not important enough to bother with making power even.
5
Thanks for the feedback everyone! I was able to get the coil functioning by using an EM filter. No more GFCI problems and the coil functions just as it did before.

Thanks again   :D
6
Hi all,

I need some help with my Class E Tesla coil/plasma speaker from Eastern Voltage Research. I currently have it playing audio over the discharge, but it murders very expensive MOSFETs. Technical support hasn’t been very helpful. They said that out of 10,000 customers, I’m the only one having trouble.

If I start the audio before starting up the coil, I kill both MOSFETs instantly. If I raise the primary 1/4” to increase coupling (recommended by EVR instructions) I kill both MOSFETs instantly.

Is this pretty much expected for these type things or is there something really wonky that I could check? I feel like if I look at it wrong, I’ll blow another $20. I’ve wasted $100 on MOSFETs now. I have video of it working as proof…

-Matt
7
Transformer (Ferrite Core) / Re: Designing a regulated HV supply
« Last post by Hiemal on Today at 03:36:19 AM »

1) What is the use duty cycle?  On for 1 second and off for 60?  In other words, how important is full-load (1mA) efficiency vs unloaded efficiency?
 It'll only ever be used at short duty cycles I believe. It'll be a point of experimentation however, since I'm not 100% certain what sort of doses seeds/plants require to get any sort of mutations. Regardless, the amount of off time will almost always be longer than the on time.

2) Is there actually any unloaded time?  (Does the X-Ray tube have any control grid, or is the supply turned on and off to time exposure?  I don't know what is typical for X-Ray tubes.)
No, no control grid; the tube I have is from an old x-ray head, and from what I can tell it's basic. The supply will be turned off/on for exposure control.

3) Roughly what capacitor values are in your 5 or 6-stage multiplier?  Would have a major impact on time constant and needed drive frequency.  Also, are the capacitors film or NP0/C0G (minimal change in capacitance with voltage)?  Or common cheap HV ceramic disk caps that have ~10% capacitance at full voltage?
 They're the standard blue ceramic HV caps; they're fairly chunky ones, if I remember right. Either 10 nF or 100 nF, rated to 20kV. or 30kV. I know, it's dumb that I don't remember precisely but I'll try to take a look at them when I get back home tonight.

4) What output ripple and accuracy is acceptable (ie for hysteresis feedback)?
If full-load time is short and unloaded time is long, then a flyback is worth considering.  Inefficient at full load, but efficiency doesn't drop much at light load.
I'd like it to be fairly accurate as far as regulation goes... 5%? 1%? I'm not sure what's considered accurate or inaccurate, but it doesn't need to be laboratory grade. Basically the preference is for me to be able to dial in something, and for me to have some level of confidence in knowing that's what the tube is actually receiving without having to fiddle with anything.

8
Solid State Tesla Coils (SSTC) / Re: Mains Ramped SSTC - Power Supply Issue
« Last post by Razerwire on June 30, 2022, 10:46:33 PM »
When using a variac without a 1:1  isolation transformer you must remember that "neutral," is bonded to earth ground inside your service panel so even with a two prong plug if you're using a non isolated oscilloscope you will cause a short. You really got very lucky!  About your power supply issue... I'm not an expert, but I have found that half wave rectified AC makes transformers rather unhappy. Now some transformers I've used handled it much better than others but what I've learned is that in 100% of cases, the less ripple in your power the happier EVERYTHING will be. For price of a few more diodes or even a simple full bridge rectifier IC, there's never a good reason to use half wave rectified AC. Another very useful rectification circuit is called a full wave doubler. Very easy to make with two capacitors and two diodes. It replaces a full wave rectifier AND doubles the voltage. Be aware that the values of your caps in a doubler will depend on where you're using it but usually you will want electrolytics and the bigger the better. In my bipolar SSTC I use a full wave doubler with 2x 250v 1000uf  low esr electrolytic caps IN SERIES. This doubles my 120v mains input and provides good full wave rectification. The big caps are important in my case especially because I do not want to draw on my bus capacitance for this and if anything, I want to add to it. Smoothing the AC ripple as much as possible. Hope this helps. -Rex-
9
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: IGBT Hookup guide
« Last post by Mads Barnkob on June 30, 2022, 10:13:37 PM »
Download the datasheet and it will tell you what connections are where.

The IGBT brick itself will have markings like C, E, G and possible some 1 or 2 added.

A half-bridge module is just two single transistors with a common terminal for their midpoint. A half-bridge brick represents either the left or right side of a full-bridge.
10
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: IGBT Hookup guide
« Last post by AstRii on June 30, 2022, 09:00:08 PM »
My best advice here is to study a bit more. Tesla coils are no joke and even experienced electrical engineers can have trouble when building high power (DR)SSTCs.

CM300 IGBTs are transistors just like any other, it's just that they are 2 in one package, it doesn't change the schematic. Read the datasheet on where is the Collector, where is the Common and where is the Emitter.
The connection between high side Emitter and low side Collector is already done for you, this is where you will connect your primary leads.
Be aware that driving a fullbridge is not just about power connections, you also need to drive all the Gates in their correct polarities.

Please, I strongly advice to read more about the topic or even make a smaller version with lower input voltages before you fry any innocent IGBT brick or even harm yourself.
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