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OverUnity Research > Benches > Itsu (Moderator: Itsu) > Jegs "HV Push Pull by Jeg" replication.
2024-05-19, 08:07:39
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Author Topic: Jegs "HV Push Pull by Jeg" replication.  (Read 7674 times)
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img  Itsu
Jegs "HV Push Pull by Jeg" replication. « on: 2023-03-19, 21:15:32 »

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While looking for a way to switch 3.5kV DC (via a MOSFET or IGBT) for another project, i found this youtube video from Jeg:

https://www.youtube.com/watch?v=manMnNOFdNI

He shows a board with 3 switching circuits each equipped with 2 MOSFET's in series able to switch some kV's, see picture.
But looking at the video alone i can not quite make up how his circuit is working, so by opening this thread, i hope Jeg (a member here) will be available to explain how his circuit is laid out.

I see / hear that there are 2 MOSFETs (1kV each) in series (total 6 MOSFET's) and there are 3 TC4420 MOSFET drivers (each driving 2 MOSFET's).
The gates of the MOSFET's are isolated by using some toroidal coils, but the setup is not clear to me.

First i think i need a diagram on how the circuit is laid out, especially how the toroidal coils are build / connected.

Secondly, do i understand correctly that each of the 2 series MOSFET's is capable of switching 2kV and that several of these 2 MOSFET's circuits can be put in series to handle 2, 4 or even 6kV?

Regards Itsu 
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #1 on: 2023-03-19, 21:25:45 »

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The circuit for which i need this HV switcher is looking like this:




Itsu
   
img  gyula
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #2 on: 2023-03-20, 00:14:16 »
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Hi Itsu,

I think Jeg used two + two MOSFETs  instead of the usual one + one  to build a normal push pull output circuit.
I think he connected the two MOSFETs as a bidirectional switch you surely heard about such, see the principle attached. I copied it from the bottom of this page: https://electronics.stackexchange.com/questions/175917/substrate-connection-when-driving-a-bi-directional-switch

In Jeg's circuit I think any one of the toroidal transformers drives two MOSFETs connected in bidirectional fashion.  Isolation is needed for driving bidirectional switches because the common source pins can be at the AC (or DC) potential that is switched by the drain pins.  Each transformer drives the common gate and common source pins directly I suppose but there is this possibility shown here:
 https://www.analog.com/en/technical-articles/transformerdriver-ic-controls-bidirectional-switch.html  but this latter circuit may not give a fast switch-off time.

Later tomorrow I return to your HV switcher with a suggestion.

Gyula
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #3 on: 2023-03-20, 07:22:19 »

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It will be better probably.
It has taken from apnote IR
But this was working bad to me.
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #4 on: 2023-03-20, 09:27:05 »

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Thanks guys,

so Gyula, you say that he uses 2 MOSFET pairs (each with 2 MOSFETs in series) to build this Push Pull configuration.

But what about this 3th MOSFET pair?
 

I understood that he can use that too to increase the voltage handling capacity of his circuit.


I will try to alert Jeg to take a look here.

Regards itsu
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #5 on: 2023-03-20, 10:38:09 »
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Hi Itsu,

I cannot see the 3rd MOSFET pair on the left side of Jeg's circuit board, it is not applied. 
And the IC socket (for the MOSFET driver IC) under the 3rd toroidal tarnsformer on the left side is also empty.

Gyula
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #6 on: 2023-03-20, 12:14:57 »

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Gyula, 

i agree, but in an internal conversation with Jeg, he mentioned:

"If all 3 switches are connected in series at the output then it can handle up to 6kV.    (1kV MOSFET's)
If 1.2kV MOSFET's are used then it can reach 7.8kV"    (I guess he meant 7.2kV.)

Waiting for Jeg to confirm.

Itsu
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #7 on: 2023-03-20, 14:55:37 »
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Hi Itsu,


Okay, it is an 'IF' possibility for all the 3 switches in series.  But not in the circuit shown in the video because he spoke about push pull circuit in the video and shown 4 MOSFETs in use, I attached a schema as I think he used them those 2 pairs in push pull as he may have showed in his video.  His 24 V battery input may include a choke coil seen at the top left side of his circuit board (looks like a tv yoke core too)  Of course the drive pulses should be 180 degree out of phase going to the gate - source inputs of the push pull stage, probably the phase invertion can be done by the drive transformers too.
 
I attached a 2nd schema I suggest to use for your 3.5 kV switching circuit, utilizing 3 pairs of MOSFETs connected all in series as per bidirectional fashion within each pair.  I took the idea from this paper
http://bromine.cchem.berkeley.edu/grppub/frbm2.pdf  The paper includes how the drive transformer is made.

I see one problem : if the input DC supply is indeed as high as 3.5 kV, then the flyback pulse after the switch-off moment may be much higher than 3.5 kV, so protection is needed. The MOV devices may be one solution. But it may be better to utilize the flyback pulses by redirecting to the output transformer primary with HV diodes (like a mechanical relay coil is clamped by a parallel diode). 

Gyula
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #8 on: 2023-03-20, 15:32:33 »

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Gyula,

so you think Jeg is switching 24V which then is being transformed up to HV?     (i think you are right about that).

This is opposite to what i want which is HV being switched so it can be transformed down to low voltage.

It makes sense to use 1kV MOSFET's as, like you mentioned lateron, the flyback pulse will be high.


Thanks for your 2nd diagram, thats about how i envisioned it, but the flyback pulse will be massive so some countermeasures will need to be taken to protect the components like you suggested.


Itsu
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #9 on: 2023-03-20, 16:26:26 »
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Hi Itsu, Gyula, all
This switching board is a generic board which i use in almost all of my experiments between about 3 Khz- 1.8 Mhz. The idea was to build a tough switch able to handle many KV. The board contains three independent switches. Each switch utilize two mosfets in series so to increase the breakdown voltage. Recently i modified it and i used lm7815 to drive tc4420 instead of 12V i had been using. This gave me more frequency range without changing turns at the gate transformer. About the isolation tx coils, i need to count their turns because i cant find any notes. The 1 uf caps especially those at the primary side need to be of a low esr or few caps in parallel with the total of 1uf.
I drive this board from my frequency generator.

If i drive all three switches with the same signal i can connect all six mosfets is series.
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #10 on: 2023-03-20, 17:32:27 »
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Hi Jeg,

Thanks for chiming in.  O0    So you do not use the bidirectional MOSFET pair as I figured but you use them in normal series connection, thanks for clarifying.  In the meantime I found an old thread here
https://overunity.com/13995/mosfet-stack-for-higher-breakdown-voltage/   you surely recall to have done the pioneering work on stacking.

EDIT:  How you meant the push pull output?  one such seriesly connected pair on one side and another seriesly connected pair on the other side, driving them out of phase?

Gyula
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #11 on: 2023-03-20, 19:48:07 »

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Jeg wanted to publish some pictures, but he says he cannot upload them here, so i will put them up here for him:


Itsu
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #12 on: 2023-03-20, 19:57:51 »
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Quote from: gyula on 2023-03-20, 17:32:27

EDIT:  How you meant the push pull output?  one such seriesly connected pair on one side and another seriesly connected pair on the other side, driving them out of phase?

Gyula
Hi Gyula. Exactly that.

If you go a little more back in time, before some nine years, you were the first who had taught me how to make a decent mosfet driver. :-)
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #13 on: 2023-03-20, 20:02:09 »
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Thank you itsu. It was more for you to see the layout as an Idea. There is a smaller board as you see at the input which is a filter for power supply decoupling.
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #14 on: 2023-03-20, 20:38:20 »

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Jeg,

OK, i see.

These blue gate isolation toroids, are these coming from PC PS's, or did you buy them separately?

Itsu 
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #15 on: 2023-03-21, 07:16:32 »
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Separately. I had chosen them according the frequency range they work with. I hope i ll find any relevant notes on this.

Ps. Thankfully i found their type. Check this link
https://product.tdk.com/en/search/ferrite/ferrite/ferrite-core/info?part_no=B64290L0618X087
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #16 on: 2023-03-21, 09:24:22 »

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Thanks Jeg,

so they are: "Ferrite (N87) core materials are an oxide made from Fe (iron), Mn (manganese), and Zn (zinc), which are commonly referred to as manganese zinc ferrites" effective up to 3MHz:
https://www.netl.doe.gov/sites/default/files/netl-file/Core-Loss-Datasheet---MnZn-Ferrite---N87%5B1%5D.pdf

Itsu
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #17 on: 2023-03-21, 11:27:44 »
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Itsu i checked the transformer and it is a 27 turns  trifiliar. So we are talking about a one to one ratio. I ll try to spot a pdf i had which provides a table with inductance vs turns vs frequency range for gate isolation transformers.
   
img  Jeg
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #18 on: 2023-03-21, 11:49:50 »
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #19 on: 2023-03-21, 21:35:18 »

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Guys,

i think i will settle for a less complex setup that Jeg has and use a mix of Jeg his setup and Gyula like this:



I need to find the correct flyback diodes across the transformer coil as there will be serious voltage to be diverted.

Itsu 
« Last Edit: 2023-03-22, 10:09:56 by Itsu »
   
img  gyula
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #20 on: 2023-03-21, 21:54:05 »
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Hi Itsu,  the schema looks good.  Yes, fast HV diodes are needed to clamp flyback spikes.
The gate driver transformer's insulation needs attention from material quality point of view.

EDIT: I wonder if the primary of the drive transformer needs a flyback clamp diode too?   C.C  (to protect the driver IC when it is just off)  Maybe an overkill...

EDIT 2: well, no need for a diode across the input of the drive transformer because the IXDI614 shunts it right after the switch off moment (shunting resistance is around 1 Ohm), 

Gyula
« Last Edit: 2023-03-22, 08:31:36 by gyula »
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #21 on: 2023-03-22, 10:25:42 »

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OK Gyula,

I have used an isolated gate transformer before when building a SSTC 2:   https://www.loneoceans.com/labs/sstc2/
It uses the UCC27425 gate driver and gate isolation transformer like shown in the attached diagram.

I used magnet wire for the transformer wire which is rated 3000V for its isolation, see the picture below.

By the way, i changed the gate driver in my above drawing from an IXDI614PI (inverting) to an IXDD614PI (non-inverting) as that is what i have and "inverting" is not needed.


Thanks,   Itsu
   
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Re: Jegs "HV Push Pull by Jeg" replication. « Reply #22 on: 2023-03-22, 15:20:05 »
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Quote from: Itsu on 2023-03-21, 21:35:18
Guys,

i think i will settle for a less complex setup that Jeg has and use a mix of Jeg his setup and Gyula like this:



I need to find the correct flyback diodes across the transformer coil as there will be serious voltage to be diverted.

Itsu

Itsu,

IMO, the schematic as shown will not successfully switch 3000v.  If you consider a positive pulse on the secondary of the gate drive transformer, both gates will be "turned on" so to speak, but the bottom mosfet will conduct through the substrate diode leaving only the top mosfet rated at 1700 Vds to hold off the 3000 volts applied to the HV transformer primary.  Avalanche of the top mosfet will certainly occur.  This type of mosfet topology will work for switching bipolar waveforms but only to a 1700v drain to source maximum.

The mosfets shown must be connected in series as previously shown by Jeg.

Regards,
Pm
   
img  Itsu
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #23 on: 2023-03-22, 15:57:52 »

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Partzman,

thanks, i tend to agree with you about the bottom MOSFET "conduct through the substrate diode".

So i have redrawn the diagram as i understand you about "The mosfets shown must be connected in series as previously shown by Jeg."

Itsu
   
img  gyula
Re: Jegs "HV Push Pull by Jeg" replication. « Reply #24 on: 2023-03-22, 16:37:06 »
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Hi Partzman,

I would like to understand the process you mention.  I assume you mean the body diode on the substrate diode, or is it a different one? I find the term instrictic diode also for body diode. Is the substrate diode not the body or instrictic diode?

I see the operation of such bidirectional switch as follows: When both mosfets are turned on,  both will conduct via their own drain - source pins. Both of their body diodes would actually be shorted by the conducting drain source channels during the switched-on moments.  The control pulse appearing across the common gate and common source pins are ground independent pulses. 
In solid state relays, power mosfets are also used in this bidirectional connection,  and AC switching is also involved for them. 

Thanks,
Gyula
   
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