Inductive Circuits - The "Classical" Approach

[FuzzyTomCat]

1) You are correct in that a "ruggedized" (i.e. avalanche rated) MOSFET can take the hammering. However, it's not quite correct to state that they were "designed" to be used this way. In fact using a MOSFET as an avalanche device is not very efficient. There are better devices (such as the diode version) that should be used for avalanche applications, such as pulse generators and voltage suppressors.

In general, active devices such as MOSFETs, BJT's etc, aren't "designed" for any specific application (yes there are exceptions). If for example you know that the switch in your application will experience periodic pulses exceeding it's rated VDS, then yes it would be a very wise choice to use an avalanche-rated MOSFET for this application.

2) The energy in the kickback pulse through the flyback diode (causing current to go back into the coil or external battery) is equal to the energy stored in the inductor prior to the switch opening (turning OFF), minus the energy loss in the inductor's resistor (10 Ohms) and the energy loss in the flyback diode itself. The fact that the voltage is higher than V+ is obviously good if we want to charge a battery, but the voltage itself is not an indication of the energy available in that pulse. When you load that pulse down (as you do when charging a battery), the voltage will drop quite a lot.

3) I have already identified the possible current paths through and around the MOSFET when it is OFF. These are via capacitances in and around the MOSFET. In the case where the flyback diode is removed, and there are large kickback spikes hitting the MOSFET, then the voltage would have to be in excess of 1000V (for the IRFPG50) to cause reverse breakdown of the body diode (actually a NPN transistor) and thus allow conduction current for the battery. From what I've seen in all the tests done by Aaron and TK (and my sims) the kickback voltage is well below 1000V.

.99

Hi poynt99,

I'm not aware that you may have seen this from "International Rectifier" Application Note AN-1005 - Power MOSFET Avalanche Design Guidelines this has some good information everyone might like.

http://application-notes.digchip.com/014/14-15377.pdf

Also another good one from "Advance Power Technology" Understanding the Differences Between Standard Mosfet's and Avalanche Energy Rated Mosfet's

http://www.nalanda.nitc.ac.in/industry/appnotes/APT/APT9402.pdf

Regards,
Glen

[poynt99]

1) All claims the spikes will damage the mosfet and that the ringing should be stopped (FACT - this mosfet IRFPG50 is designed EXACTLY for this kind of application)

2) All claims that the spike would be too small to be significant (FACT - on a decent circuit the voltage is 4 times the input voltage, it charges batteries or caps - it is VERY significant)

3) All claims that when the mosfet is off, the battery cannot conduct and therefore won't receive a charge (FACT - the diode in the mosfet allows just this exact current conduction as it is designed to do this!)

1) You are correct in that a "ruggedized" (i.e. avalanche rated) MOSFET can take the hammering. However, it's not quite correct to state that they were "designed" to be used this way. In fact using a MOSFET as an avalanche device is not very efficient. There are better devices (such as the diode version) that should be used for avalanche applications, such as pulse generators and voltage suppressors.

In general, active devices such as MOSFETs, BJT's etc, aren't "designed" for any specific application (yes there are exceptions). If for example you know that the switch in your application will experience periodic pulses exceeding it's rated VDS, then yes it would be a very wise choice to use an avalanche-rated MOSFET for this application.

2) The energy in the kickback pulse through the flyback diode (causing current to go back into the coil or external battery) is equal to the energy stored in the inductor prior to the switch opening (turning OFF), minus the energy loss in the inductor's resistor (10 Ohms) and the energy loss in the flyback diode itself. The fact that the voltage is higher than V+ is obviously good if we want to charge a battery, but the voltage itself is not an indication of the energy available in that pulse. When you load that pulse down (as you do when charging a battery), the voltage will drop quite a lot.

3) I have already identified the possible current paths through and around the MOSFET when it is OFF. These are via capacitances in and around the MOSFET. In the case where the flyback diode is removed, and there are large kickback spikes hitting the MOSFET, then the voltage would have to be in excess of 1000V (for the IRFPG50) to cause reverse breakdown of the body diode (actually a NPN transistor) and thus allow conduction current for the battery. From what I've seen in all the tests done by Aaron and TK (and my sims) the kickback voltage is well below 1000V.

.99

[poynt99]

There's still one component missing in the capacitive circuit posted here to make it 100% "equivalent" to the inductive circuit. Presently, as the circuit stands there is no "flyback diode" to curtail the big spike as we have (now abandoned in the RA circuit) in the inductive version.

Anyone know what it is and where it would go?

.99

OK, now on to some rebuttals...

[poynt99]

Hi .99, please relax, your first post (#1) SPECIFICALLY states CAPACITIVE OVERUNITY CIRCUITS.

Here it is:

Right,

I was asking the new age folks from their point of view the question.
It's not something I would be asking a classicist.

It was a challenge out to all, and in particular the new age folks, to show the "effect" in a capacitive circuit...is there OU with caps?

Anyway, a small oversight on my part. Apologies. I thought it was pretty obvious the viewpoint I take based on the title of the thread.

Cheers,
.99

[Altair]

Hi .99, please relax, your first post (#1) SPECIFICALLY states CAPACITIVE OVERUNITY CIRCUITS.

Here it is:

Before discussing anything directly about this subject, I would like to ask any individuals that have a "new age" slant on these topics, a question pertaining to "Capacitive Overunity Circuits".

To start, surely all would agree that inductors and capacitors are true opposites, or as one person says "mirror images of each other". Also, check out his circuit half way down the page....looks quite familiar. Odd he hasn't discovered any overunity in his testing

Here's the question:

If inductive circuits (particularly the inductive kickback type) are perceived and apparently metered to exhibit COP>1, then please illustrate an example of a complementary capacitive circuit that does the same.

.99

[poynt99]

Tough Crowd

.99, I took a second look at your interesting circuit.
I just realized that I1 is a current source, so it will (theoretically) supply any required voltage to keep the charging current flowing in C6.
When the shunt mosfet turns ON, C6 discharge current flows up through the load. A big spike of current will be generated, of course. If the load is a capacitor, its voltage will get pumped-up by the action of the 2 diodes and C6. Somewhat like a boost regulator.
However, I don't see OU here... please enlighten me.
P.S. Ideally, I1 should be gated, as to not continuously try to feed current through a shorted mosfet.
P.S. 2 If the load is inductive, there will be a recirculating current established through the load. Maybe OU could be attained here ?

Thanks for the brain teaser.

I wish folks would read what is actually posted. Sure would save a lot of trouble.

Anyway, again, if y'all read the posts, I said clearly that this is not about OU per se. In fact the whole point of this exercise was to establish the parallels between the inductive and capacitive circuits, and that if it can be clearly shown that although the familiar spikes can be produced in the capacitive circuit (similar to but "transposed" in comparison to the inductive circuit), that one would come to the conclusion that neither circuit exhibits OU!

Boy, you guys are a tough crowd sometimes. LOL.

.99

[Altair]

.99, I took a second look at your interesting circuit.
I just realized that I1 is a current source, so it will (theoretically) supply any required voltage to keep the charging current flowing in C6.
When the shunt mosfet turns ON, C6 discharge current flows up through the load. A big spike of current will be generated, of course. If the load is a capacitor, its voltage will get pumped-up by the action of the 2 diodes and C6. Somewhat like a boost regulator.
However, I don't see OU here... please enlighten me.
P.S. Ideally, I1 should be gated, as to not continuously try to feed current through a shorted mosfet.
P.S. 2 If the load is inductive, there will be a recirculating current established through the load. Maybe OU could be attained here ?

Thanks for the brain teaser.

[poynt99]

Do a bit of study rather than ranting on with opinion

Milehigh, when you found one Ying-Yang Part, it doesnt mean, you can take that for everything

And if you think, Coils replace Capacitors, well,
then we then now we can build all E-Motors with Capacitors, and save all this Coils because the EM Field is the same. Ahaha-ha.

Point is, to not to say its impossible to build it with Capacitors,
i dont think, it works with Capacitors, you need at last one Inductive Element,
and not only a Cap, what cause a Short at a certain Point and has changing Resistance down to zero like a Cap has.

The Answer is allready given at Post #40 from Altair.
Thanks for that, Altair.

Joit, are you listening at all?

Altair is actually wrong in his "guess" that the capacitive circuit would be inefficient. Opinions are welcome but they don't hold much water I'm afraid. To say "I think this one would be awfully inefficient if built." is just that, an opinion. There is no basis in fact.

When comparing the efficiency of a circuit employing an inductor vs. one with a capacitor, the capacitive circuit could be more efficient. What makes inductors inefficient is their inherent DC resistance. It's something that just can not be eliminated. In comparison, capacitors of large value generally have significantly less series resistance (called ESR for caps), and therefore less energy loss. We can make more efficient coils using high permeability cores and large wire, but there are distinct limitations here as well.

When and if either of you gents actually take the time to understand how the circuit works, then you will have a leg to stand on at least.

ASK if you don't understand. We're all here to learn (including myself) and help each other.

.99

[Joit]

Milehigh, when you found one Ying-Yang Part, it doesnt mean, you can take that for everything

And if you think, Coils replace Capacitors, well,
then we then now we can build all E-Motors with Capacitors, and save all this Coils because the EM Field is the same. Ahaha-ha.

Point is, to not to say its impossible to build it with Capacitors,
i dont think, it works with Capacitors, you need at last one Inductive Element,
and not only a Cap, what cause a Short at a certain Point and has changing Resistance down to zero like a Cap has.

The Answer is allready given at Post #40 from Altair.
Thanks for that, Altair.

[MileHigh]

Zealots:

I have something that might get some hearts beating, the Exar XR8038 and XR2206 voltage-controlled oscillators. Some of the hair-pulling over using oscillators as function generators could be made easy with these chips. Be sure to check out the links, and then search on "<chip> application notes" and have fun.

Both of these chips can produce sine waves with about 1% distortion, which is pretty decent. Some may not know that a pure sine wave, and a voltage-controlled one at that (as easy as pie) is a very important "research tool" for looking at circuits. A pure sine wave has a frequency spectrum that consists of two spikes, okay - one spike, but it is really two for those in the know. Don't be confuse this with a "voltage (time) spike", this is a "frequency spike."

You even get true triangle waves. ooohh... lol

And now for the almighty links:

https://www.jameco.com/Jameco/Products/ProdDS/34972.pdf

XR8038 pdf, XR8038 description, XR8038 datasheets, XR8038 view ::: ALLDATASHEET :::

To get real power out of it, you would need a DC-coupled linear power amplifier circuit. You could probably use any stereo amplifier, but be bandwidth-limited. You might have to hack into a stereo amplifier to get pure DC-coupling. For sure there are these power MOSFET or BJT modules that go into car audio amplifiers. A brave soul could buy one and play with that. It's a palm-sized amplifier module, all you have to do is give it a beefy power supply and add a few support components.

You could end up with one high-class voltage-controlled signal generator with adjustable gain and bandwidth and high power output. Use 10-turn pots for the voltage control.

MileHigh

PS: From glancing at the pdf files, one, probably both, run on up to a +/-15-volt supply, so the output waveforms are very high in amplitude. That means the gain setting on your DC-coupled power amplifier can be set to unity or less for an output waveform with the same or less amplitude. This is _very_ good news. The power amplifier output will be very stable and low-noise because the voltage gain is unity or less. You are effectively lowering the output impedance of your waveform, giving it the ability to source or sink a large amount of current into a load and maintain the same output voltage. Typically the output from an amplifier module is a differential output (difference in voltage between two separate outputs), so one of your differential outputs becomes the ground for your circuit. Just be aware that this ground is NOT the same as your battery and/or power supply ground that powers the amplifier module and you should never connect the two together. However, a separate and independent battery can still be added to the circuit if need be. The independent battery's ground can connect to the ground derived from the differential amplifier output. This independent battery will "hitch a ride" on the differential amplifier output circuit ground and not be "aware" of this.

[poynt99]

Oscillating Circuits

Mosfets are used in many applications specifically because they oscillate so well. I have done the research after learning about Rosemary's circuit and it is all over the web from industry references, massive amount of patents on self oscillating mosfet circuits, audio circuits, etc...

Even on IRF's website in all the technical docs, they give you many scenarios and values of components for the mosfet to oscillate at different frequencies. It is all right there. I know because I took the time to look it up.

I agree the oscillation should not be required to achieve a gain according to how the circuit is supposed to work.

[MileHigh]

Joit:

> I dont think, that Caps do replace Coils.
With Caps you only rumbel the Current/Energy around, and with a Coil you have a EM Field what is more 'elastic' and has inductive Current still.

The capacitor stores the electrical energy in the electric EM field that exists in the space between the two plates of the capacitor.

The coil stores the electrical energy in the magnetic EM field that exists around the coil.

The "elasticity" of the capacitor's electrical EM field will try to sustain voltage, and changing voltage results in changing current.

The "elasticity" of the coils's magnetic EM field will try to sustain current, and changing current results in changing voltage.

Once more the Yin-Yang complimentary relationships between capacitors and coils are revealed.

Time to eat more Spice....

MileHigh

[poynt99]

Harvey, you out there?

@Harvey.

Are you interested in backing up and defending some of your statements?

I've commented on several points which can be found on the first page of this thread.

.99

[poynt99]

Thanks MH.

I had no doubt that you would "get it".

Altair and Joit, I'm not sure you are getting it.

The point was to demonstrate an equivalent of the inductive version using a capacitor. It has nothing to do with efficiency or OU, and it's not specific to RA's circuit. I've clearly showed that there is a capacitive circuit equivalent to the inductive one.

Joit, it would seem that you did not even give any thought to how the circuit works. How can you dismiss it based only on opinion? I would encourage you to examine how it works. It might give you some insight into the inductive circuit as well.

So, aside from MH, if anyone doesn't understand anything about how this circuit works, please don't hesitate to ask. There really is no difference between the two circuits, other than as MH mentioned, basically the currents and voltages are transposed.

If the circuit is understood, I invite anyone to illustrate where or how the circuit would operate OU. What is the OU mechanism here? If the inductive circuit exhibits OU, then surely this one must also. Please show how.

How would Rosemary's zippon (or whatever) theory transpose to the capacitive circuit?

A really big sheww indeed

.99

[MileHigh]

.99:

Excellent example! I am rusty and did not think to "transpose" the voltage source for the inductor circuit into a current source for the capacitive circuit.

A coil integrates voltage over time to give you a magnitude of current flow through the inductor.
A capacitor integrates current over time to give you a magnitude of voltage across the capacitor.

It's all so "elegant."

I prefer to use the term "Yin-Yang." It is kind of apropos in the sense that you are always playing with two variables, the "through" variable and the "across" variable, for both of these energy storing devices.

Look at caps and inductors for almost any paramater for any type of excitation and this "Yin-Yang" complimentary pattern is readily evident.

I guess that "current source" would be an enigmatic concept for a lot of people in your audience.

In fact there is one staring us in the face all the time: The heating resistive component of the coil-resistor acts as a current source when it is dissipating electrical energy and turning it into a "flow" of heat energy. This heat current source is charging the thermal mass of the body of the coil-resistor. The body of the coil-resistor is a thermal capacitor. Finally, the heat coming off of the hot coil-resistor is due to the fact that there is an equivalent thermal resistance to "ground" (the ambient temperature).

So here is the "heat" circuit: A current source charging a capacitor in parallel with a resistor. The "through" variable is the heat flow (current) and the "across" variable is the temperature difference between the coil-resistor body and the ambient temperature (the voltage).

We know that the energy in (the heat flow) must equal the energy out (dissipation of heat from air convection and radiation). If there is no balance then the capacitor keeps on charging until something gives, i.e.; the coil-resistor material starts to get friendly with the oxygen in the air. Therefore the temp of the coil-resistor rises with an exponential curve and starts to even out at the "final voltage" where the same heat flow in has to become the heat flow out.

This is why just measuring the temp of the coil-resistor body under controlled conditions is such an accurate way of comparing the running circuit power and the pure-DC-equivalent power. Even if the thermal resistance is likely somewhat non-linerar with respect to temperature, you are still left with the fact that the energy in must equal the energy out.

Well, that was a long-winded way of saying that the electrical energy dissipated inside the coil-resistor body acts like a current source in the "thermal electrical circuit" that models what is going down in the real world.

Really big sheww, .99, really big sheww....

MileHigh