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1
Transformer (ferrite core) / Re: How to design a 7.5kV AC source?
« Last post by CristianM on Today at 09:31:14 PM »
Thanks for the suggestions. I'll try to implement them.
2
Great Job, I really liked the article !
3
You have to choose a frequency on which you will design your SMPS around, it could be a range within those that you find from different smps driver ICs if you decided to use one of those.

But lets just say that chose 300 kHz, then you can adjust the driving parameters on the duty cycle, turning up/down on the power output.

The calculators that sjsimmo linked to looks very good for a start to get an idea of the topology, choosing a core/switches etc.
4
Transformer (ferrite core) / Re: How to design a 7.5kV AC source?
« Last post by Mads Barnkob on January 19, 2019, 04:46:02 PM »
Hi Cristian and welcome to HVF

All your specifications would be reachable with a ferrite core with a HV winding and driven by a half-/full-bridge. The frequency is however what makes this less trivial, you would most likely need to make a voltage modulator to get such low frequencies.

I got no experience in the following suggestion, its just an idea I just had when thinking about how defibrillators work. You could form a high voltage pulse through a large output inductor to slow down the current and get a sine wave from a square input.
5
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by Hydron on January 19, 2019, 11:07:22 AM »
The 75N60s were fine hard switching 225A (their rating), I suspect you could get away with a bit more than this with resonant switching but haven't tested them at higher currents than this. They won't be as resilient when grossly overloaded as a brick, but if you pop a set then they are also cheap to replace!

Edit: I wrote this reply based on the first page, didn't see page 2. Comments still stand but it sounds like you've already done some testing to failure :P
6
Dual Resonant Solid State Tesla coils / Re: My First DRSSTC
« Last post by sjsimmo on January 19, 2019, 08:08:58 AM »
So I had my first IGBT failure recently  :(

One of my IGBTs has always noticeably run warmer than the others (for unknown reasons), and I suspect this to be the cause of the failure. The coil had not been run in over a week, and so had been packed up since the last full power run. I ramped the coil up to 240VAC input. Everything seemed normal for about 5 seconds. However, before i could turn the interrupter from 10uS on-time up to 50uS on-time, one half of the bridge failed short circuit (Gate, Collector and Emitter now read ~0 ohms on both IGBTs), blowing up the 3A slow-blow fuse in my variac. Neither of the IGBTs have any sign of physical damage on the package. Is it normal for IGBTs to fail without any visible damage, and when not operating at full-power?

Thanks again for your help, everyone :)
7
Hi FilipŠebík,

I came across this website a while ago: http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.html when I was trying to design an smps lab power supply (I never got round to actually finalizing the design or building it though...).
It contains calculators which may be helpful with working out the suitability of your core, and required wire thickness.  :)
I'm sorry I can't help with doing the calculations though, I don't understand much about the mathematics myself...

Hope this helps,
- sjsimmo
8
Hello, I want to make my own SMPS, but I can never find a way to calculate the VA rating for a ferrite core and I want to know who knows the equation for calculating VA rating and or the required turn/frequency for wanted or max wattage or something.

I would use this core FERROXCUBE ETD49/25/16-3F3 https://www.tme.eu/en/Document/882e54fb8772e021c51c30b1d1879eab/etd49.pdf
and I would like to make at least 500-600W variable voltage power supply (if the core is suitable), but I don't know the calculations required to do this. But for now let's have a fixed IN, OUT voltage and out A
Let's say the PSU will work with 230V AC, so 325V Peak, the power of 600 watts, Max current input of around 3 amps and the output voltage of 60 volts and output current of 10 amps and the switching topology is half bridge using mosfets.

How do I get the required turns/operating frequency and wire thickness for the primary and turns and wire thickness/turns for the secondary with the values that are written in the datasheet? I found this
Quote
Using the Ampere's law, you can get the following equation:

E = Ae² * B² / (2 * AL)

E: energy stored in the magnetic field
Ae: core's effective area
B: maximum flux density allowed by the core material
AL: core parameter, depends on Ae, magnetic circuit lenght and air gap lenght

You see, power (P) is enery by time. More energe and less time will result in a higher power.

P = E / t

The input power at the inductor is the energy stored (E) divided by ton. Ton is the duty cycle (D) divided by the switching frequency (fsw).

P = E / ton = E * fsw / D

This is an aproximate way to determine how much power you can obtain from a certain core. Actually there are losses by eddie currents, joule effect and stray flux.
But this equation needs the operating frequency for power calculation, so I can't learn much from it.
 
Helpful info
The 3F3 core parameters from Ferroxcube website:



PS: I am not asking you to calculate the things for me, just to help me and/or show us the equations for the things so it helps the people that will look for it
9
Transformer (ferrite core) / Re: How to design a 7.5kV AC source?
« Last post by profdc9 on January 18, 2019, 04:25:14 PM »
I'll venture a solution...

Use a full-bridge or H-bridge of MOSFETS such as the IRF820, where each side is driven by two 50% duty cycle square wave signals of different frequencies with a difference between the frequencies that is the output frequency you want that would drive both sides of a small ferrite transformer primary.  For example, if you want 1 kHz, you would drive one side perhaps with 200 kHz, the other with 201 kHz.   You could rectify mains power for example to power the H-bridge, for example, from 220 VAC to 300 VDC, with a full-wave rectifier, and use a buck converter or even a small variac on the primary side to adjust the DC voltage on the bridge.  A ferrite transformer, for example, with a 10:350 turn ratio so that you could transform the 300 VDC voltage up to the 7.5 kVAC range.  A high voltage polypropylene capacitor (perhaps 1000 pF?) would need to be placed on the secondary output of the transformer to filter high frequency (200 kHz) and leave a clean sine wave, or you might have to build a pi lowpass filter if you want the high harmonics really attenuated.   You will probably also need a DC block capacitor as well in series with the primary winding.   What I've described is open loop and I think to close the loop you would need to use an optoisolator to feedback a signal to the buck converter to regulate the voltage, or you could just put a resistive load (like a 10 megaohm 10 watt resistor) to try to provide some stability to the output voltage and act as a bleeder resistor if you don't need super accurate output voltage.

Dan


10
Transformer (ferrite core) / How to design a 7.5kV AC source?
« Last post by CristianM on January 18, 2019, 03:48:06 PM »
Hello! I need to design a high voltage AC source with the following specifications:
- 7.5kVpp max. output voltage;
- adjustable output voltage;
- isolated output;
- sine wave output;
- adjustable output (sine wave) frequency in the range 40Hz-2kHz;
- max. 1 mA output current.

Can someone recommend a possible solution? A basic transformer or flyback supply (maybe recommend some components, schematics) or even a commercial solution?
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