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Woo-Woo MOSFET switch question

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Nikša

May 7, 2018
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Its maximum threshold voltage is 6V for some of them to conduct only 0.25mA. Then some of them will not do anything with a gate to source voltage of only 5V. It needs a gate-source voltage of 10V for it to turn on pretty well.

Yes i know, i am considering this function generator which can output 20Vpp. I will also need a driver since impedances are 4 to 50, so this FG couldn't drive it into saturation by far. At IXYS they recommended one of these.
 
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Nikša

May 7, 2018
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@Nikša: Although you have self-identified as noob in your post #5, your later response in post #16 seems to indicate some understanding of physics with a willingness to add electronics to your repertoire. Good for you. And having a multimeter is a good start. You can use it to rustle up some free electrons, among other things.:D

You clearly misunderstood, i'm a noob for semiconductors only, not for electronics and physics. In fact, some things i do would seem impossible or "magic" to you. Let's just say electron is a deflected magnetic field, always a wave, never a particle. As such, these can be easily created with no input energy whatsoever, if you know how. I'll just say "static" magnetic field is not static at all.


The problem of driving the gate-to-source at low voltages, in the presence of a large voltage on the source with respect to power supply common, comes up frequently., especially in high-side H-bridge drivers for large motors. H-bridge drivers usually solve the problem with a "charge pump" circuit for the high-side drivers.

It appears you want to place a conducting MOSFET in series with a high-voltage capacitor and then turn the MOSFET off to interrupt the discharge of the capacitor into some sort of circuit. A typical use might be to control the exposure from a xenon gas-discharge arc lamp after a certain level of light exposure is reached. The problem is the source terminal is operating at the same potential as the drain terminal when the MOSFET is on. You need some means to isolate the gate-to-source low-level drive signal from this voltage. Two means come readily to mind: optical isolators and pulse transformers. Neither circuit is particularly simple. And you may still need a charge-pump circuit to obtain the desired bias levels.

It would help us to help you if you just explained what it is you are trying to do.

Yes, i want to interupt discharge from a HV cap into some solenoids, use doesn't really matter here. "You need some means to isolate the gate-to-source low-level drive signal from this voltage." So you're saying low voltage signal can't drive HV MOSFET directly, contrary to what AnalogKid said above. Do you mean once MOSFET is ON, input signal won't be able to turn it off cause "source terminal is operating at the same potential as the drain terminal"?

Oh, and on electron motion... most of us responding here are aware that those of us in good physical shape can easily outrun an electron traversing a wire. I like to use the analogy of people trying to run through a crowded tunnel or tube and having to bump into each other, dodge and weave to find a path. The speed of an individual electron in a conductor has nothing to do with current, which by definition is measured in units of charge-per-second passing a given point. One coulomb of charge moving past a point in one second represents a current of one ampere, no matter how fast individual electrons are moseying along. A coulomb of charge is represented by a fairly large number of electrons, about 6.2415 × 1018, so moving that many electrons past a given point on a wire every second represents one ampere of current, no matter how fast or slow individual electrons may require to "cross the finish line". Take a look at electrolysis for some practical applications of moving electrons from one place to another.

Indeed, as i said above, current represents transfer of energy or Poynting Vector, not the electrons themselves. Electrons could be liked to balls in Newton's cradle, and current to transfer of momentum due to oscillations of the static balls.

And just in case nobody has mentioned it yet: Welcome to Electronics Point!

Thank you.
 
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Hopup

Jul 5, 2015
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If I guess right what you want to do, you want to use industrial type of IGBT's for it. You should understand high voltage safety quite well if you are going to play with devices like that.
 

Nikša

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If I guess right what you want to do, you want to use industrial type of IGBT's for it. You should understand high voltage safety quite well if you are going to play with devices like that.

I understand high voltage safety and i was considering a lot of IGBTs, but their voltage and frequency are limited, up to 1200V for 30-60kHz (there are some expensive ones that can handle few kV) and 600V for 150kHz. I am considering one of these but it's a trade off. MOSFET i mentioned before can switch up to 2 MHz.
 

Hopup

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Ok, after that I'm not completely certain what u actually want to do. What kind of voltage and frequency do you need?
 

Nikša

May 7, 2018
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Ok, after that I'm not completely certain what u actually want to do. What kind of voltage and frequency do you need?

The MOSFET i mentioned before (up to 4.5kV at up to 2MHz) will do.
 

Hopup

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Maybe you could achieve same effect using LC spark gap circuit?
 

Nikša

May 7, 2018
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Maybe you could achieve same effect using LC spark gap circuit?

Maybe. I guess i could add a HV diode to produce pulsed DC which is what i want. But then i could not vary the frequency, unless i change inductor or capacitor - maybe with that haircomb cap like used in a radio. I don't know, MOSFET seems simpler way to go and more precise frequency wise.
 
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(*steve*)

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You clearly misunderstood, i'm a noob for semiconductors only, not for electronics and physics. In fact, some things i do would seem impossible or "magic" to you.

Now you are being offensive.

And you don't know the background of people here.

Also, magic is performed by either misdirection, sleight of hand, or with hidden information or devices. If you intend to play magic tricks with us here then you're not going to get a lot of useful help but you will piss a lot of people off.

And unless your experience is with vacuum tubes, your statement is bordering on a non-sequitor.

People are trying to help you. I would recommend you lose the "I am so superior" attitude and help us help you by explaining WHAT it is you're trying to do.

We frequently find that an attitude like yours is held by people whose threads end up in the woo woo science section.

Even if I were to take you at your word that you are experienced with electronics but not with semiconductors, I would still have to tell you that the is a lot about MOSFETs that we haven't discussed yet. Some of those things are not obvious and some of those things could mean the difference between a functioning circuit and a smoke emitter.

You may be able to get around trying is what you are doing by defining the characteristics of the circuit completely, but it is far easier to simply say what you're doing.

If it is so secret you can't tell us, then you would be better off hiring somebody competent and getting them to sign a non disclosure agreement.
 
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Nikša

May 7, 2018
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I am sorry that you see it that way cause i wasn't offensive nor expressing superiority in any way, i am grateful for the help of the forum members, they have all been polite and helpful in some way.

I used the term "magic" only to describe the common disbelief toward overunity devices. Ironically, it is not only possible but very simple to obtain energy with no energy input apart from the underlying energy field permeating all space everywhere. There are MANY ways to do this, with moving parts or solid state. This is not "non sequitur" nor "woo woo science" but the REAL science, of which, what you call "science" is but small, very limited part.

This is beyond the scope of this thread, but i'll give you a simple mechanical example. You sure heard of Newton's 3 laws. But rare know there is a 4th law describing conversion of assymterical centrifugal force into linear acceleration. This phenomena has been known since 19th century, i only defined it as a law and termed it 4th law of motion cause it is in a way, an extension of Newton's 3 laws. It states:

"Asymmetrical centrifugal force of unbalanced masses converts into linear acceleration of the system."

It means that unbalanced mass oscillating within 180° or less, or spinning 360° with varying speed, accelerates the whole system unidirectionally without interacting with any outside medium apart for the space itself.

In other words, if you were floating in space (or sitting on an office chair, a small boat or ice..) and you swing your arms forward (in opposite directions to cancel the back-torque), you would accelerate forward as if someone pushed you from behind. So simple and self-evident, yet still considered "impossible". This also makes the death of Matt Kowalski from Gravity very ironic.

This is possible due to the fact rotational reference frames are non-inertial and in them virtual forces act - centrifugal force. In other words, virtual forces do not comply to “laws” of action and reaction in linear sense, neither to conservation of momentum and energy (thermodynamics).

So, there are no limitations in nature except those man imposes upon himself by ignorance or false belief. But this is getting out of the subject.

Now you are being offensive.

And you don't know the background of people here.

Also, magic is performed by either misdirection, sleight of hand, or with hidden information or devices. If you intend to play magic tricks with us here then you're not going to get a lot of useful help but you will pots a lot of people off.

And unless your experience is with vacuum tubes, your statement is bordering on a non-sequitor.

People are trying to help you. I would recommend you lose the "I am so superior" attitude and help us help you by explaining WHAT it is you're trying to do.

We frequently find that an attitude like yours is held by people whose threads end up in the woo woo science section.

Even if I were to take you at your word that you are experienced with electronics but not with semiconductors, I would still have to tell you that the is a lot about MOSFETs that we haven't discussed yet. Some of those things are not obvious and some of those things could mean the difference between a functioning circuit and a smoke emitter.

You may be able to get around trying is what you are doing by defining the characteristics of the circuit completely, but it is far easier to simply say what you're doing.

If it is so secret you can't tell us, then you would be better off hiring somebody competent and getting them to sign a non disclosure agreement.
 
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