Did you try to tune the series resonant circuit?
Look for a faster transistor which still meets your requirements.
The gate shows a bit of ringing, some resistance in series with the gate will lower it a bit, but the drawback is that it makes transistor slower.
I suggest to read about class E's principle of operation and its design equation e.g. "Generalized Design Equations for Class-E Power Amplifiers with Finite DC Feed Inductance" from IEEE.Yes I did try to change the L2 value and C3 value, but it did not help too much. I am not sure which component is the key to get I want.
You have to keep in mind that in practice nothing is ideal, including your 0.2 ohm Rds(on) which may keep you away from achieving what you want.Hi CataM, do you think the transistor is the key in making the wired waveform in switching node? I do not have other transistors available at this moment, but if that can solve my problem, I will add a series resistor to the gate.
I suggest to read about class E's principle of operation and its design equation e.g. "Generalized Design Equations for Class-E Power Amplifiers with Finite DC Feed Inductance" from IEEE.
I would kindly give that paper to you but forum rules does not allow it. Anyway, it should not be hard to find it.
You have to keep in mind that in practice nothing is ideal, including your 0.2 ohm Rds(on) which may keep you away from achieving what you want.
Obviously the closer to ideal operation of the circuit, better will perform. I do not think 100% that the ringning in the gate can solve anything, but a faster transistor yes since this is a ZVS operating circuit.
C2=33pF, L2=4.2Uh
C3=100pF, L3 is 7.8uH
I want to have a 15V Vpeak to peak amplitude of the Vcoil, but I can never get it using the exsiting circuit.
Current is restricted to a small level by your small C values. You need an L:C ratio which is associated with greater current levels. This will give you more current going through the coil. That is what you really want, isn't it?
There are other LC oscillators which might work better for you. Consider this one.
The long-tail pair automatically senses the resonant frequency of the LC tank. It provides an energy 'kick' at the right time in the cycle. Sine-shaped oscillations build and sustain.
(I built a hardware version and it works. Mine was low current and low frequency.)
Notice peaks of 1/2 A going through the coil. Supply voltage is about 4V. I included a fraction of an ohm resistance in the coil (in an effort toward realism in simulation). Less than 1/10 A is required from the supply.
To adjust output level, change supply voltage, or adjust resistor R.
It is possible to get voltage swings of much greater amplitude than the supply voltage. Select a very large L:C ratio (capacitor value very small in relation to the inductor). However the large amplitude does not guarantee you have a lot of current going through the coil. Furthermore the sinewave may become distorted. It's the capacitor playing a dominant role in setting the current level. It sets it very low. In turn the inductor creates higher voltage levels. I saw it with my own eyes. Waveforms at 20V amplitude when the supply is only 5V.
I suggest to read about class E's principle of operation and its design equation e.g. "Generalized Design Equations for Class-E Power Amplifiers with Finite DC Feed Inductance" from IEEE.
I would kindly give that paper to you but forum rules does not allow it. Anyway, it should not be hard to find it.
You have to keep in mind that in practice nothing is ideal, including your 0.2 ohm Rds(on) which may keep you away from achieving what you want.
Obviously the closer to ideal operation of the circuit, better will perform. I do not think 100% that the ringning in the gate can solve anything, but a faster transistor yes since this is a ZVS operating circuit.
L1 is a large one but it seems it does not play a critical role
This is the inductor near the supply V+. I believe it acts the same as a boost converter.
(1) First it is grounded by the mosfet for a while.
(2) Current builds to 1A or more.
(2) The mosfet shuts off.
(3) Inductive kick sends a jolt of current into the righthand portion of your circuit. (The supply voltage is added to the emf.)
(4) The combined components ring for a few cycles (6.8 MHz), at high amplitude (20 or 30 or 40V).
If I have the correct idea, then the above sequence sends a few cycles at high voltage to the transmitting coil, then it waits a while. (So perhaps it is not designed to generate a sinewave continuously? My post #7 schematic generates a continuous sinewave.)
Questions that arise:
* Does the paper instruct to drive the mosfet at 7MHz, or at a lower frequency, say, less than 1 MHz?
* What results do you get when you increase the value of L1 (the inductor closest to supply +)? When you increase it to 1 uH?
Look the delay time and fall time. Total on time is delay + rise time. To see if it is faster, just look to the delay time.Would you tell me which parameter I should check in the FET datasheet to see if it is a faster transistor?
In your paper they said they used inductors with Q=120 if I recall.One thing I am not sure on this board is the high Q inductor. In this paper, it said the inductor of L-type matching network should be with high Q. However, I did not find the Q information from the inductor I was used. It is a 1.5uH inductor that can support 15A DC current, which was used for buck converter.
Look the delay time and fall time. Total on time is delay + rise time. To see if it is faster, just look to the delay time.
However, I think this should be done at the very end after the circuit is matched perfectly... and your circuit is not very slow, comparing ns to the switching frequency, so the faster transistor can wait.
In your paper they said they used inductors with Q=120 if I recall.
Q of coil can be calculated by ωL/ESR with ESR = DC resistance of the coil.
For the chocke, use a magnetic core for it, not with air core like the Tx coil.
Look the delay time and fall time. Total on time is delay + rise time. To see if it is faster, just look to the delay time.
However, I think this should be done at the very end after the circuit is matched perfectly... and your circuit is not very slow, comparing ns to the switching frequency, so the faster transistor can wait.
In your paper they said they used inductors with Q=120 if I recall.
Q of coil can be calculated by ωL/ESR with ESR = DC resistance of the coil.
For the chocke, use a magnetic core for it, not with air core like the Tx coil.
One thing I am not sure on this board is the high Q inductor. In this paper, it said the inductor of L-type matching network should be with high Q. However, I did not find the Q information from the inductor I was used.
Going with your schematic in post #8, the single biggest improvement is to increase your center inductor to 5.5 uH. My simulation gets peaks over 2A in the transmitting coil.
Two loops act in resonance (at 6.8 MHz)... C1-C2-L2 & C2-C3-L3. One goes clockwise while the other goes counter-clockwise, then they switch directions.
Notice volt levels over 100V (theoretically, that is).
As a general rules you can get high Q by minimizing ohmic resistance in components. My inductor models have a small ohmic resistance inline. If your real components have less resistance then your transmitting coil may reach greater power levels.
Possibly a tiny core of metal improves performance? A core concentrates magnetic flux within the inductor, and reduces interference between inductors which are located nearby.
In case I need to reduce the peak voltage level, do we have any simple solution (such as adding a R/C)?
Obviously Class E rectifier boosts efficiency, but is it needed ? Can you afford a bulkier and more expensive design? That bad is your bridge rectifier ?What I have now is only a full bridge rectifier (https://www.infineon.com/dgdl/bas4002...29a6dc9f802b68), is it possible if I build a class E rectifier to boost the power capability?
The output capacitance Coss of your FET is far too high to work effectively at 6.78MHz. By a factor of ten at least. No improvement to the Q of your inductors or capacitors is going to make this circuit function well.
You need to either select a much more optimal FET, or decrease your operating frequency greatly.
Actually it's much higher than 325pF. Coss is a nonlinear function of Vds. At your low bias Vds, you will effectively get 500-1000pF.(1) the COSS of F12N10L is 325pF, so you think using this FET can make my board not functional at all?
Efficiency and functionality are inherently linked, since being too inefficient may destroy the FET.Acutually I have to operate at 6.78MHz but I do not care about the efficiency. As far as it is functional, it is good enough for me.
Probably, yes. A large Coss can be dealt with somewhat by lowering L1 to resonate with it. But then you aren't dealing with a true class E amplifier anymore.(2) Now I have a 470pF in parallel with D and S terminals. Do you think reducing it will help?
That would certainly help, but you should consider the tradeoff of all FET parameters. Vdss, Ron, Coss, thermal impedance, etc. To start with you should define how much drive current/voltage you will need (which comes from your coil parameters and the desired power on the secondary). From there you can select a Vdss, then Ron and Coss.(3) If you think COSS is the cause of my circuit, I suppose I need to look for a FET with around 30pF COSS?
The obvious things to try, is reduce supply V, or reduce bias to the transistor/ mosfet. Start small and ramp up to your intended power level.
Also be mindful about the Ampere level going through components. Who can say whether a little 470pF capacitor can endure, when it has 2A going back and forth through it 7 million times a second? And what volt rating do yours have? 50V is typical for small ceramics.
It's a good idea to monitor heat. And put a protective cover over your circuit, in case something explodes.
Actually it's much higher than 325pF. Coss is a nonlinear function of Vds. At your low bias Vds, you will effectively get 500-1000pF. Efficiency and functionality are inherently linked, since being too inefficient may destroy the FET.
Probably, yes. A large Coss can be dealt with somewhat by lowering L1 to resonate with it. But then you aren't dealing with a true class E amplifier anymore.
That would certainly help, but you should consider the tradeoff of all FET parameters. Vdss, Ron, Coss, thermal impedance, etc. To start with you should define how much drive current/voltage you will need (which comes from your coil parameters and the desired power on the secondary). From there you can select a Vdss, then Ron and Coss.
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