Circuit resonance

[johntee]

Hi,

I've posted a basic circuit on my NTL homepage and need some help with it.
Would a forum member take a look and maybe help answer my questions on the webpage. Here's the link:

**broken link removed**

Many thanks, I'm a novice on electronics but trying to learn a little each day.

John

 

[ljcox]

There are formulae available to calculate the inductance of a coil.

Answers:-
1. Yes, but D3 will severly dampen the reasonance.

2. No, the magnet will just add a "DC" bias to the field. However, the core may saturate on one half cycle.

3. I don't know. It depends upon whther neodymium is conductive. If so there will be eddy current losses which will dampen the oscillation.

4. Yes, but you need to ensure that the amplitude of the oscillation is within the limits of the FET

5. When the FET turns on, the voltage across the coil will start at 12 Volt and then decay expontentially to a value determined by the resistor and the coil resistance (provided that the pulse is long enough)

When the FET is turned off, D3 will clamp the back EMF at about 0.6 Volt; this will decay to zero if the off pulse is long enough.

I suggest you use circuit simulation software to simulate the circuit so you can see the waveforms.

 

[johntee]

Thanks Len, great reply and really, really helpful, need to locate software now, maybe on a trial basis.

Kindest regards

John

 

[ljcox]

John,
You're welcome.

It is a bit complicated, so it is difficult to fully express it in a verbal description. Hence a software simulation is better.

There are free simulation programmes available. The one I have is called
Switcher CAD III. I assume it is still available and still free.

 

[johntee]

Hi Len,

Once again you excell, I've managed to pick up a copy of Switcher CAD III from their website. Nice little tool, now comes the learning curve, how to interpret the information correctly. No magic wands in the electronics game it seems, what you put in you get out so to speak. Ummm, now that statement sounds familiar.< wink wink >

Thanks once again,

John in the United Kingdom

10:00 PM GMT

 

[ljcox]

Good morning John,
There are experts in this forum who can help you with Switcher CAD.

good luck,

 

[abbarue]

Maybe this circuit simulator will help:
https://www.falstad.com/circuit/

 

[johntee]

Simulator

Hi,

Thanks for your input, the simulator is great, a picture / animation speaks a thousand words, really nice people out there, you amongst them.

Cheers again,

Johh in the UK

9:46am, GMT

 

[johntee]

Simulator

Hi,

Thanks for your input, the simulator is great, a picture / animation speaks a thousand words, really nice people out there, you amongst them.

Cheers again,

Johh in the UK

9:46am, GMT

 

[Hero999]

What's the purpose of the 820R and 220R potential divider on the MOSET's gate?

Why does the 555 timer circuit have 100R in series with it?

You can look up LRC circuits on Wikipedia if you want to calculate everything but simulation software is probably the easiest option.

What's the purpose of your circuit?

You don't have to add a time stap to your posts, the forum software does it for you.

 

[johntee]

Hi everyone,

Sorry for the delay in answering, grandkids are very demanding !!

The circuit is actually off the internet with the INDUCTOR (L) coil added to the output stage. This is the actual text from the author:-

"The output voltage from pin 3 of the second NE555 chip is reduced by the 220 ohm / 820 ohm resistor combination. The transistor acts as a current amplifier, capable of providing several amps to the output electrodes.
The 1N4007 diode is included to protect the MOSFET should it be decided at a later date to introduce either a coil (“inductor”) or a transformer in the output coming from the MOSFET, as sudden switching off of a current through either of these could briefly pull the ‘drain’ connection a long way below the 0 Volt line and damage the MOSFET, but the 1N4007 diode switches on and prevents this from happening by clamping the drain voltage to -0.7 volts if the drain is driven to a negative voltage."

I kind of understand this but I'm a real novice where electronics are concerned, hence the request for forum members help.

From my personal perspective, I was hoping to drive the Inductor coil (L) with pulses of varied frequencies via the 555 and the MOSFET and add these to the static magnet field of the (L) coils neodymium magnet core surface. This neodymium magnet core actually has a static gauss strength of 10000 and I was hoping to add the circuits output to this and create a pulsed radiation field. I want to then apply those varying increased pulsing fields to biological matter and view any changes which might take place in such.

Freaky stuff eh? Well not really, magnets and magnetic pulsing has been used quite openly to assist injuries to bone breaks etc, and give pain relief due to its apparent anti-inflammatory action. Football physiotherapists use low & high frequency pulsers daily to aid healing on their players. There's a new field of Electro-medicine which is testing various pulsing magnetic devices on Cancer and tumour lines. Now that's interesting.

There you go Hero999 and friends, the full story in a nutshell. maybe the "nut" of the latter word is applicable to me, who knows?

Oh yes, I now realise I don't have to add a time stap to my posts. Thanks for that, my inexperience shines through once more!

Speak soon,

John

 

[johntee]

Hi again Hero999 and friends,

I have downloaded a time trial version of Multisim simulation software as advised but it blowing me over a bit. I can't seem to progress because the Footprints of certain devices are unfamiliar to me. To save you downloading I put a link to my Homepage showing part of my basic circuit counter schematic using a 741 and a 4017 decade counter, if anyone can help me I'd be obliged.

**broken link removed**

Cheers for now

John

PS. In respect to the above request, and for other new users of Multisim, the program automatically allocates VCC and GROUND to component footprints to keep wiring to a minimum.
My decade counter is now working beautifully from the pulses of the LM741 opamp. You learn a little each day. Great !!!

 

[ljcox]

Hi everyone,

Sorry for the delay in answering, grandkids are very demanding !!

The circuit is actually off the internet with the INDUCTOR (L) coil added to the output stage. This is the actual text from the author:-

"The output voltage from pin 3 of the second NE555 chip is reduced by the 220 ohm / 820 ohm resistor combination. The transistor acts as a current amplifier (actually it is a switch, not an amp), capable of providing several amps to the output electrodes.
The 1N4007 diode is included to protect the MOSFET should it be decided at a later date to introduce either a coil (“inductor”) or a transformer in the output coming from the MOSFET, as sudden switching off of a current through either of these could briefly pull the ‘drain’ connection a long way below the 0 Volt line (wrong, it will be a very high positive spike - this would damage the FET) and damage the MOSFET, but the 1N4007 diode switches on and prevents this from happening by clamping the drain voltage to -0.7 volts (wrong, it will clamp it to about +12.7 Volt) if the drain is driven to a negative voltage (misleading, the drain voltage is being switched between about +7.9 Volt and 0 Volt, it does not go negative)."[/I]

I kind of understand this but I'm a real novice where electronics are concerned, hence the request for forum members help.

From my personal perspective, I was hoping to drive the Inductor coil (L) with pulses of varied frequencies via the 555 and the MOSFET and add these to the static magnet field of the (L) coils neodymium magnet core surface. This neodymium magnet core actually has a static gauss strength of 10000 and I was hoping to add the circuits output to this and create a pulsed radiation field. I want to then apply those varying increased pulsing fields to biological matter and view any changes which might take place in such.


John

John,
I've added some comments above in red.

Do you have any info on the neodymium? Is it conductive?

As I said in previous post, if it is conductive it will limit the upper frequency due to eddy currents.

Also, if you want is to resonate, you will have to remove the diode. Note that the capacitor will prevent the hugh spike that would occur if it and the diode were not there.

You could connect the diode between the drain a source (cathode to the drain) to protect the FET from negative peaks.

If you fire up your circuit simulator, you should be able to see what is happening. Try it with and without the cap in parallel with the coil and also, with the cap removed, with and without the diode. Then connect both cap & diode and see what happens.

Also download (if you have not done so already) the data sheet of the MOSFET so you know its maximum ratings.

 

[johntee]

Hi Len,

Thanks for your circuit comments I'll make note of these for future reference. I don't know how to tell if the magnetic core in conductive unless I can use a meter. It just looks like a dark brown material but is extremely powerful.

The diode across the Drain to Source is a most welcomed piece of advice, again it's gone into the old gray matter for future reference.

Many thanks again,

John

 

[ljcox]

Hi Len,

Thanks for your circuit comments I'll make note of these for future reference. I don't know how to tell if the magnetic core in conductive unless I can use a meter. It just looks like a dark brown material but is extremely powerful.

The diode across the Drain to Source is a most welcomed piece of advice, again it's gone into the old gray matter for future reference.

Many thanks again,

John

John,
You're welcome. I suggest you try to find info on the neodymium magnet, eg. do an internet search.

Measuring it with a meter may be inconclusive as the surface may be non conducting, ie. it may have an oxide or other type of film.

Another way to do it would be to use a ferrite core and a DC current superimposed on the AC current to provide the "DC field" with the AC imposed on it, ie. don't use the magnet. This has the possible disadvantage that you may saturate the core. So you need to know the magnetic properties of the material.

However, as I said in a previous post, the saturation issue also applies to the neodymium magnet, ie. it may be saturated by the AC field when the AC field is in the same direction as the "DC field".

 

[johntee]

Hi Len,

RE: Measuring it with a meter may be inconclusive as the surface may be non conducting, ie. it may have an oxide or other type of film.

You've hit the nail on the head again. I've been on my magnet suppliers website and they reveal this:

"Our Neodymium-Iron-Boron magnets are approximately 75 iron, and have a surface protector to prevent corrosion"

The iron in the magnets construction suggests saturation problems

In respect to your suggestion, Another way to do it would be to use a ferrite core and a DC current superimposed on the AC current to provide the "DC field" with the AC imposed on it, ie. don't use the magnet

Do I take it that a ferrite core is preferable to the neo-magnet then, or could I just use a strong ferrite magnet within the inductor? Maybe it's back to the drawing board, Len.

As explained to Hero999 in my previous post, my main aim was to superimpose and add the circuits varying pulsed output upon the magnets very impressive static gauss of 10000, thus giving a larger overall field strength. This would hopefully give me a larger depth of magnetic penetration into biological materials.

Kind regards as usual,

John

 

[ljcox]

"Our Neodymium-Iron-Boron magnets are approximately 75 iron, and have a surface protector to prevent corrosion"

The iron in the magnets construction suggests saturation problems.

Do they provide a B-H curve? This would help you to see whether there is a margin between the static flux and the saturation level.

In respect to your suggestion, Another way to do it would be to use a ferrite core and a DC current superimposed on the AC current to provide the "DC field" with the AC imposed on it, ie. don't use the magnet

Do I take it that a ferrite core is preferable to the neo-magnet then, or could I just use a strong ferrite magnet within the inductor? Maybe it's back to the drawing board, Len. I'm not an expert on magnetics. The point of ferrite is that it can operate at higher frequencies than an iron core.

The same question as above occurs to me about ferrite, ie. see if you can find a B-H curve for a ferrite magnet.
As explained to Hero999 in my previous post, my main aim was to superimpose and add the circuits varying pulsed output upon the magnets very impressive static gauss of 10000, thus giving a larger overall field strength. This would hopefully give me a larger depth of magnetic penetration into biological materials. I'm certainly not an expert in this area. But I'm dubious about your claim that the static component will give you a deeper penetration.

I wonder whether you simply need a strong alternating field or, as you claim, a static one with an AC component. Note that you may not be able to make the latter alternate. To make it alternate, the AC component has to be stronger than the static field so that on "negative half cycles" the magnetic field reverses (which is what I mean by alternating). Otherwise, is it just a static field with an AC variation - if you see what I'm trying the say.

Kind regards as usual,

John

John,
As I said above, I'm not an expert in magnetics. So I suggest to glean as much as you can from the manufacturer's web sites and the internet in general.

Perhaps you could start another thread in this forum asking for advice on the properties of ferrite.

 

[johntee]

Hi Len,

Your response is impressive and factual from my limited knowledge. I'm far from an expert in any field and thus I'm at the mercy of those who freely choose to impart their knowledge to me. Of this I'm truly grateful. My aim, as previously stated, is to acheive as maximum a penetration of biological materials as possible, in as great an alternating + varying field strength & frequency as possible, within what I believed was achieveable via my origininal concept of static field (neo magnetic inductor) + that of the added and created pulsed fields from the circuitry. I must convey honestly that I'm not the most adept or able person to impart my ideas and concepts to others, but I do hope I can achieve such a realisation of my intents in my somewhat naive way via you and friends on this forum.

In my minds eye I visualise the reality of adding something to that which already exists, i.e. neo-magnetic gauss + ?, but cannot claim any expertise in that area of static magnetics + a pulsed electronic content.

Likewise I cannot make any claims to my beliefs or visualisations of this concept because I don't possess that expertise in any capacity.

Len, on this basis, and from your electronic experience, do you believe, without predjudice of course, that what I'm aiming to achieve with my revealed concept is viable with just a strong alternating field as you suggest?

RE: But I'm dubious about your claim that the static component will give you a deeper penetration.

For clarity, it's revealed that all static magnets have a known 'Magnetic Permiability depth' of all materials to varied extents. Therefore it seems reasonable to conclude that such a fixed content can be added too with the correct pulsed magnetic content via circuitry electronics. Once again, maybe I'm totally wrong in my inspired concepts. I personally make no claims.

I do relish and appreciate our communications and hope I don't outstay my welcome with my enthusiasm in this area.

Kind regards

John in the UK

 

[johntee]

Ooops,

Sorry Len, the last point went well over my head in my eagerness to achieve.

RE: Perhaps you could start another thread in this forum asking for advice on the properties of ferrite.

Yes, you are correct, I've probably exhausted everybody with my questions and I'm truly appreciative of their advice. I not one to impose upon those who have been so generous, and thank yourself and others for their contributions. Hopefully some day people will say of me as I aspire in knowledge, " I knew of him, and he helped me." A truly worthy acknowledgment.

Truly, thank you once more,

John in the UK

 

[ljcox]

Ooops,

Sorry Len, the last point went well over my head in my eagerness to achieve.

RE: Perhaps you could start another thread in this forum asking for advice on the properties of ferrite.

Yes, you are correct, I've probably exhausted everybody with my questions and I'm truly appreciative of their advice. That's not what I meant. See below. I not one to impose upon those who have been so generous, and thank yourself and others for their contributions. Hopefully some day people will say of me as I aspire in knowledge, " I knew of him, and he helped me." A truly worthy acknowledgment.

Truly, thank you once more,

John in the UK

John,
I did not mean to imply that you stop adding to this thread.

What I meant is that the people who have the magnetic expertise may not necessarily be reading this one given the subject heading "Reasonance"

So if you start a thread with a subject line such as "Advice needed on ferrite materials" or something like that, you may attract the right audience.

I'll now go back to your previous post and answer it.