HF switcher supply construction and voltage multiplication

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
Pierre_Thourault
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HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Hello everyone,

I've thought for a few days about the electrical parts of the fusor. So first of all I was thinking to use some micro wave transformers in serie but after reading the FAQ about the voltage multiplication the " High Frequency (HF) switcher supply construction with voltage multiplication" pick my attention. So I've made some google researchs and found nothing in french then I started doing my research in english and of course found something but way too complicated both for my english level and electronics level...

I'm a bit discouraged but maybe some of you can help me undersand the main principles that is to say the differents stages of the circuits.

Thanks in advance ;)
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Alright i’ve done some research and i think i’ve an exemple of what kind of circuits it is :
- use an instable multivibrator to get 2 squares waves signals a high frequency ( in the order of kHz)
- use these 2 signals with 4 MOSFET to create an AC
- with the AC, increase the voltage in a homemade transformer
- with a cw voltage multiplier, rectify and get a negativ hot

Is this the process used in a HF switcher ? Or am i totally wrong xD ?
John Futter
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Re: HF switcher supply construction and voltage multiplication

Post by John Futter »

You are on the right track
But this is not easy
read the appropriate forums here. There are people who have modified or made from scratch these sort of supplies, but not many due to difficulty.
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thank you for your answer John,
I’ve followed your advice : read some threads about HV and I’ve come across this :

“This power supply has 5 main stages to generate HV:
230 V AC Step-up converter to 400V DC
Buck converter for controlling the HV (+-100 kHz)
H-Bridge to drive the transformer (+- 50 kHz)
Flyback type transformer (1:5 ratio)
Cascade multiplier that has voltage and current feedback “

So i guess the Buck converter is used as a variac to control the input voltage isn’t it ?
And can you use, as i’ve said an instable multivibrator, to drive the H-Bridge at 50 kHz ?
Another question of mine is : if we end up with 400 VDC and pass the current through a transformer with a 1:5 ratio then we get 2000 VDC which is definitely not enough

I carry on looking for answers since i would like to create a working fusion device that will be finish I hope this summer
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Rich Feldman
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Re: HF switcher supply construction and voltage multiplication

Post by Rich Feldman »

The term "flyback type transformer" can be ambiguous. Flyback-looking physical shape, or flyback electrical operation?

As used for making high voltage in CRT televisions, and low voltage in inexpensive switchmode voltage converters,
the flyback converter topology can produce voltage ratios much higher than the secondary/primary turns ratio.
Magnetic part is operated as coupled inductors, not as a transformer.
Primary current builds up while a switch is "on". Secondary voltage (based on turns ratio) is usually insufficient to get any secondary current in that direction.
When switch opens to interrupt the primary circuit, the voltage magnitude on primary winding goes much higher than primary bus voltage.
Secondary voltage goes higher by the same turns ratio, enough to turn on a diode and deliver secondary current to a HV load (such as a voltage multiplier). Voltages during that phase are determined by the secondary circuit and load.
All models are wrong; some models are useful. -- George Box
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thank you for your answer,

I think i understand: it uses the same principle as in a boost converter and I guess it’s the physics behind the video of electroboom about taser. So when the voltage needed in the secondary coil is high the impulsion of current mustn’t take long in order to conserve energy.
Victor Gonzalez
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Re: HF switcher supply construction and voltage multiplication

Post by Victor Gonzalez »

Pierre I'm glad someone is using what I wrote.

I will re-upload the photos in that post.

It's flyback by principle, not physical shape, where there's energy stored in the magnetic field. The core is gapped and with primary square wave, the secondary is a senoidal wave.

The senoidal output (2000V) of this transformer is fed to a fullwave cascade multiplier  (Cockcroft-Walton multiplier) that makes the -20 to -50 kV.

You can skip the step-up and buck and use a variac with a fullwave bridge rectifier, those are needed in that PS because it requires very stable output.
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thank you Victor for your answer, it will be very nice to see those pictures ,

I’m not sure i understand the relation between the H-Bridge and the flyback converter ( we are talking about flyback converter not transformer ? ) so normally to run the converter you need a square wave trough a MOSFET but then why is there a sinusoidal in the secondary ?

And could we use only a half wave cascade rectifier ?
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Re: HF switcher supply construction and voltage multiplication

Post by Victor Gonzalez »

You can use half wave cascade, the ripple will be bigger.

I re-uploaded the pictures in this post:
viewtopic.php?f=11&t=12887

Secondary Voltage without load:
20190505_195423.jpg



Secondary Voltage with resistive load
20190505_194646.jpg



Transformer:
20190505_194650.jpg


20190403_164628.jpg



400 V Step Up and PFC
20180719_154116.jpg



Buck - H-Bridge
20180719_154131.jpg
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Well sh*t 😂
It’s very hard too understand so I think I’m gonna try to design a circuit on my own and then i’ll show you to make sure it is well. Besides i think this thread will be helpful for others peoples who try to build this kind of circuit.
So I was thinking to do this :
- Step up the voltage AC 220 V - 50Hz and rectify it
- Buck converter to control the voltage from ] 0V ; maxVoltage [ and use a NE555 to control the time the MOSFET is on and off
( it is aimed to replace the Variac because it’s too expensive for me )
- use a H- Bridge with an instable multivibrator ( in order of tens kHz ) to create the AC current
- make a homemade transformer
- pass the current through a Voltage multiplier

My questions are :

1/ why the HF makes the transformer smaller ?
2/ how can we know that there’ll be enough current and power ?
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

This is an illustration of what I'm talking about
This is an illustration of what I'm talking about
Victor Gonzalez
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Re: HF switcher supply construction and voltage multiplication

Post by Victor Gonzalez »

Pierre_Thourault wrote: Tue Mar 03, 2020 11:40 am
circuit elect.JPG
This circuit has everything, the problem will be making it work like it's idealized. You will have to face many problems. example: what type of core will you use on your inductor? Ferrite saturates easily with DC, Iron-Powder? How will you design your HF transformer? working nearly in saturation is good short circuit protection, etc....

I would use a chip like UC1825 or 3825 and IR2113 driver on the power transistors for the H-Bridge and buck
John Futter
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Re: HF switcher supply construction and voltage multiplication

Post by John Futter »

Victor is on the right track
I see that you have not provided any protection for the transistor bases or collectors.
Any transformer with a large ratio will have relatively high leakage inductance which will cause reflected high voltage artifacts into the primary this via capacitive coupling so there is no ratio reduction like the turns ratio.
all of this is known by EE's -hence this is why high voltage high power supply design is considered almost a black art.
I see your circuit is of the self oscillating type that is usually suited to output powers of up to 100 watts..
I also see that there is DC coupling to the transformer primary --this leads to early saturation due to core walk from assymetrical DC drive conditions
As already stated it is far better to use a proper driver chip and series resonate the primary with a series cap to stop core walk saturation
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thanks a lot for your answer Victor and John,

I need to look up what you have suggested me then I will surely come back to you with an improve design.

Sum up of what you have told me ( please could you tell me if there's something I misunderstood )

- It seems like I have a problem with how to drive the H Bridge and buck so you suggest me to do it with a chip like UC1825 or 3825 and IR2113 driver on the power transistors.
- Also I need to work on the inductors I will use
- there is how to make a proper HF - HV transformer with a high turn ratio too
- and finally I need to protect the transistors

I have few questions :

- "there is DC coupling to the transformer primary " I dont get it because the H bridge outputs AC ?
- I have thought about why HF reduces the size of the components but I still don't understand so could you please explain me why I have precisely decided to do this kind of circuits xD

There is a lot of work but at least I'm helped so thanks again ;)
Pablo Llaguno
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Re: HF switcher supply construction and voltage multiplication

Post by Pablo Llaguno »

Not very familiar with electronics as advanced as what you want, but perhaps this thread can give you some ideas viewtopic.php?f=11&t=13134

Good luck
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thank you very much Pablo for this link !

It cleary answers most of my questions and is very well structured : perfect for someone who doesn’t know a lot about electronics like me.
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Hello everyone
Since i don’t have school due to a certain viruse I can focus on this.
So i was thinking why not use a driver from a tesla coil like a DRSSTC and maybe also use the secondary rectified. Has it already been made ? Or is it stupid for some reasons ( maybe it disturbes the resonant frequency so that’s why you can’t use the secondary)
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Re: HF switcher supply construction and voltage multiplication

Post by Jon Rosenstiel »

Pierre,

Maybe this will help...

viewtopic.php?f=11&t=4569&p=29680&hilit ... ing#p29680

JonR
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Thank you Jon,
I have read the web site of steve Ward but I don’t understand the sine wave. How the LC circuit resonates if the IGBTs are off ? because the inductor and the caps are in series.
I think I’m going to build this kind of driver which can be used also in a TC since I am very interested in building a Tesla Coil ( playing music with a TC must be incredible) and as I don’t have many bucks to spend, building the same driver for the TC and the fusor will allow me to spare money.
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

I think I understand how the circuit resonates: is it thank to diodes across IGBTs ? Also I’ve read that the caps are aimed to smooth a peak of voltage but where does it come from ?
I’m gonna put a screen of the circuit so you may help me more easily
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

772A5E93-6B1B-4534-9616-7DD6C9940DCA.png
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Hello everyone,

So after many times trying to understand the Capacitor Charging Power Supply (CCPS) using the Series Load Resonant (SLR) of Mr Carl Willis. I've decided to come back to a more classic design.

However I don't give up on the CCPS as I will do my best to understand it (by the way if anyone reading this can help me or has done this cicuit, you may email me via the forum ) so I'm trying to contact Mr Carl Willis, Mr Steve Ward and Mr Marco Denicolai ( if you know them may you please inform them that I email them since I have used very old email address I'm not sure they will get my email). For me, I'll learn more and more about this circuits.

But anyway, the goal of using the same driver for my future DRSSTC ( Double Resonant Solid State Tesla Coil ) and my future fusor is achieved : I am gonna send a picture of the circuit. Please tell me if you have suggestions, remarks or if you spot a mistake.

I hope everyone is fine in this period of pandemic !
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Circuit 3.PNG
John Futter
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Re: HF switcher supply construction and voltage multiplication

Post by John Futter »

again no base or C,E protection
probably more silicon sacrifice to the gods of high voltage
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Bob Reite
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Re: HF switcher supply construction and voltage multiplication

Post by Bob Reite »

LOL! Reminds me of the very first AM solid state transmitter. No protection for the output devices. The MW-1A model got the protection diodes. I suggest that you do the same.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
Pierre_Thourault
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Re: HF switcher supply construction and voltage multiplication

Post by Pierre_Thourault »

Hello everyone,

I have modified the circuit with diode between C and E. I have also added an inductor to smooth the ripple and limit the current. I have put a fuse too.
What do you think about these modifications ? Are there some mistakes ?

Now the next step is to finish the design completely without any errors, then find the values of all components. And after that I will try to simulate the circuit to make sure everything is OK. Then ... THE BUILD !

Pierre
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