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 » Sat Feb 22, 2020 5:27 pm

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 » Sun Mar 01, 2020 3:13 pm

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 » Sun Mar 01, 2020 5:42 pm

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 » Sun Mar 01, 2020 10:13 pm

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 » Sun Mar 01, 2020 10:52 pm

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 » Mon Mar 02, 2020 6:45 pm

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 » Mon Mar 02, 2020 6:57 pm

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 » Mon Mar 02, 2020 8:03 pm

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 ?

Victor Gonzalez
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Re: HF switcher supply construction and voltage multiplication

Post by Victor Gonzalez » Tue Mar 03, 2020 2:19 am

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 » Tue Mar 03, 2020 3:56 pm

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 ?

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