Magnetic CARA - Proof of Concept

[Verpies]

16.3mH @ 10Khz without ferrite

...and with the ferrite?

18.5 Ohm DC resistance

...that's a lot

Screenshot:
yellow: voltage across C2
blue:    voltage across C1
green:  current through L1

That's a clean classical waveform.
I especially like the 5:1 ratio of current's rise time to fall time.

Pulse period 10ms

If the timebase is 1ms/div then the scopeshot shows 5ms.

Calculations:
C1 39.82uF @ 30V = 17919uJ
30V - 17.6 = 12.4V

Unfortunately that 17.6V difference includes noise amplitude.
You should measure from the average of the blue trace (a horizontal center line) before C1's discharge to the the average (horizontal center line) after C1's discharge.

[Verpies]

Right now I'm trying to write a sim for a free running version of CARA that will recycle the energy back into the supply capacitor,

Similar to this one ?

That will recycle the energy back into the supply capacitor

Won't that interfere with easy Out/In energy measurements?

When I get the basic idea finished, I will transfer the circuit to the real world variable inductance setup. (the sim doesn't allow for variable inductance)

Mine does not either.
Even the legacy equations are deficient when analyzing the mechanical energy gained by a movable core, but they can handle the variable inductance.

It will be based on a flyback converter with spring loaded movable core materials operating at mechanical resonance.

So with two windings, yes?  What turn ratio do you consider?
Coincidently, the design Itsu had built was based on the inverting buck-boost converter.

I've been thinking this could also be attempted with a small amplifier feeding the core and a position sensor, pickup coil or accelerometer to provide positive feedback.

Yes, I was thinking about one of those MEMS accelerometers, too, albeit more to gauge the mechanical energy gained by the core.

Such a method may have been used in the TPU, i.e. letting the coils sing or squeal at their acoustic resonant frequency with an acoustic feedback sensor of some type feeding the amplifier that drives the coils. So simple, no wonder we may have missed it.

Yes, this effect might also appear at acoustic pulse repetition frequencies.

[Verpies]

Currently I am working on high-speed (DC-DC supplied) insulated multilevel gate drivers. (without optos!)

Such gate drivers allow for the construction of fast [ns] Solid State Relays (that's what these two MOSFETs in series oppositions are) which make it possible to work around the evil* Miller effect and allow MOSFETs to be used in place of diodes (for synchronous rectification) and bidirectional switching as well as for high-side switching with N-Ch MOSFETs (which have a lower R_DS(ON) and are cheaper than P-Ch)

Besides obvious applications in this CARA experiment, such galvanically isolated gate drivers are also useful in all kinds of motor driving schemes, full H-bridges, solar regulators , battery chargers, DC-->AC inverters, PWM servos, etc...
They also completely avoid the inconvenient ground loops between scopes and signal generators.



* The Miller effect occurs in all inverting switches/amplifiers (such as transistors working in common emitter or common source modes) where a capacitance exists between the output and the input.  This effect is responsible for slowing down of transistor's switching speeds and sometimes is responsible for parasitic Miller oscillations that waste a lot of energy.  
In MOSFETs, it occurs anytime the voltage between the drain and the gate changes rapidly (high dv/dt).  However when an isolated gate driver is used, then it is possible to operate the MOSFET in a non-inverting common drain configuration (a.k.a. the source follower) and avoid the high dv/dt between its drain and gate, altogether. 
Because of this, the transistor switches faster and cannot suffer from Miller oscillations and ground loops.  The burden of the high switching dv/dt is transferred from the transistor to the isolation barrier of the driver.

[Verpies]

It is interesting to watch these videos to see some common flaws of Schottky diodes:

For those lurkers that want to brush up on the basics of MOSFET switching, body diodes and advantages of high side switching with N-Ch MOSFETs, I recommend theses video tutorials below:

The last video (#6) uses optocoupler isolation and no isolated DC-DC conversion for the output stage of the gate driver (it uses a bootstrap capacitor instead) so it is related albeit much slower and less versatile than the isolated gate drivers, I am currently working on.

The first video (#2 at 5m15s) illustrates  the advantage of a MOSFET's conduction over a diode's conduction (30mV drop vs. 700mV drop) which is the basis for higher efficiency of synchronous rectification over a diode rectification.

[Itsu]

...and with the ferrite?

With ferrite 600mH (inner pot core leg has an air gap of 0.8mm).

...that's a lot

Yes,  but its a big pot core (7cm od)

That's a clean classical waveform.
I especially like the 5:1 ratio of current's rise time to fall time.

glad you like it 

If the timebase is 1ms/div then the scopeshot shows 5ms.

Right,   FG pulse 10ms @ 50% duty cycle

Unfortunately that 17.6V difference includes noise amplitude.
You should measure from the average of the blue trace (a horizontal center line) before C1's discharge to the the average (horizontal center line) after C1's discharge.

Yes, i toke the number in the boxes for ease of calculation



Great info in the video's
Interesting your work on high-speed (DC-DC supplied) insulated multilevel gate drivers. (without optos!)


Regards Itsu

[ion]

Similar to this one ?
Won't that interfere with easy Out/In energy measurements?
Mine does not either.
Even the legacy equations are deficient when analyzing the mechanical energy gained by a movable core, but they can handle the variable inductance.
So with two windings, yes?  What turn ratio do you consider?
Coincidently, the design Itsu had built was based on the inverting buck-boost converter.
Yes, I was thinking about one of those MEMS accelerometers, too, albeit more to gauge the mechanical energy gained by the core.
Yes, this effect might also appear at acoustic pulse repetition frequencies.

Q1 No it is a bit different I'll post it when I get the sim working to my satisfaction.

Q2 I won't be making Pin/ Pout measurements, rather I will be using a bench supply to keep the supply capacitor topped off via a diode, then by tuning the system, as less power is required, the PS feed current should decrease, possibly go to zero or near zero, the supply cap is free to rise above the power supply feed voltage, if anomalous energy is available. If the supply current goes to zero, The circuit is recycling 100%+ into the supply capacitor.

Q3 The two windings will be close to 1:1 wound bifilar to reduce leakage inductance. Two windings so that the circuit can be easily configured to return energy to the supply capacitor.

[Verpies]

Interesting your work on high-speed (DC-DC supplied) insulated multilevel gate drivers. (without optos!)

They are very versatile devices.
For example they can be used to construct bidirectional & very fast [ns] Solid State Relays (SSR), such as these below:



Note that the SPST electromechanical relay is a 4-terminal device, while the SSR is a 5-terminal device ( because of the additional need for V_CC ).
Conceivably, you could connect the V_CC and the input together in order to make the SSR a 4-terminal device, but then the SSR would become very sloooww and its input would draw a lot of current.
Also, note that the IGBT SSR always exhibits V_CE(SAT) + V_F logarithmic voltage drop of the IGBT and the diode, respectively, which usually amounts to 2.6V, because the current always flows through one of the diodes and one of the IGBTs, while the MOSFET SSR does not exhibit any nonlinear voltage drops (only linear resistive 2*i*R_DS(ON) drop), since current always flows through both of the MOSFETs.

[Verpies]

As is my Universal Switch.  
http://www.overunityresearch.com/index.php?topic=2594.0

Yes, this is the same idea but different implementation.
The largest difference is the lack of optos.

The high power switching components are not integral parts of my isolated gate driver, but both MOSFETs and IGBTs can be driven by it.

Q: Why MOSFETs are used in the CARA experiment?:
A: Because MOSFETs behave like linear mΩ resistors when they are closed, while IGBTs behave like logarithmic diodes when they are closed.  This also means that IGBTs can conduct only in one direction while MOSFETs can conduct equally well in both directions when they are closed.   See this video.
In an IGBT SSR, the 2.6V voltage drop of the C-E junction +  the foward voltage drop of the diode ( V_CE(SAT) + V_F ) would represent a prohibitive energy leak in the CARA experiment.
That's also why MOSFETs can be used to switch HiFi audio signals (and RF), while IGBTs cannot do so without distortion and diode-like voltage drops.

MOSFETs are also much faster than IGBTs (especially when turning off).
However, in MOSFET SSRs when 2*i*R_DS(ON)  > ~2.6V then IGBT SSRs can outperform MOSFET SSRs.  This happens only at high blocking voltages and at high conduction currents (i) and at low frequencies [kHz].

I am working only on a DC-DC isolated multilevel gate driver which can drive MOSFETs as well as IGBTs (with negative gate voltages for faster fall times, AC)
I am not using optocouplers because they are very slow and have a short lifetimes.

I have a question about your DC-DC converter:
What is the measured capacitance of its galvanic isolation barrier ?