A 'ZVS' style oscillator optimization problem

[NyaaX_X]

Hello friends. Here I try to make a 'ZVS' oscillator that can operate at hundreds kHz. And wish that can easily directly driving a tesla coil. There I see some "advanced version" of the 'ZVS' oscillator like using mosfet to replace the diodes. And I imagine a IC driving one. Make a draft of it with LTspice. But it seems the zvs and efficiency of it is not quite good... could someone help me that? The zip file contain my draft and .lib file of some components.

And if somebody already made this circuit before. That I'm sorry for that..

#############
>>> ZVS.zip <<<
#############

The mosfet driving ZVS

My Draft

[davekni]

For adding a gate driver to ZVS oscillator circuits, I'd suggest looking at these posts:
    https://highvoltageforum.net/index.php?topic=2340.msg17128#msg17128
and the link within that post:
    https://hackaday.io/project/162935-piernass-fast-zvs-mazzilli-driver
and a class-E push-pull circuit that is very similar to ZVS oscillators and runs at high frequency:
    https://highvoltageforum.net/index.php?topic=2469.msg18153#msg18153

[NyaaX_X]

Wow, Thank you Dave !!

After the post I go to bath and later I searched some of them the similar topics. In my draft I use the classic self-oscillate circuit but add gate driver to mosfet parallelly. Sorry for I have not read all of those pioneers' project. But in the simulation I try to push the frequency to 1MHz and the result seems not too bad.

Now I am thinking the duty cycle or the "dead time" of each mosfet have some problems, or maybe I have to add the tuning capacitors to mosfets like Class-E circuit.
If you have time maybe run my LTspice simulation and give me some hints ~ thank you very much.

[Anders Mikkelsen]

I've played a bit with inductance fed parallel resonant halfbridge circuits, of which the classic "ZVS" circuit is the simplest possible form. My experiences were:

1: It's critical to have some conduction overlap in the two transistors, in order to not get overvoltage spikes from interrupting the current in the DC link inductor(s). This conduction overlap is only guaranteed by the balance of turn-on and turn-off times in the transistor, which is not a well controlled parameter, especially when people use whichever transistors they can find.
2: Conduction overlap is problematic though, since it essentially shorts out the tank circuit. Depending on the tank impedance and VARs, and the actual overlap time and frequency, this can represent significant power loss in the devices.

To deal with (1), it's good to enforce some overlap using RC delays, but this makes (2) worse. The common solution for larger CFPR inverters is to have diodes in series with the switching devices to block this current, this makes it possible to have an arbitrary amount of overlap. Then a bit of phase lead is required to ensure ZVS. As long as all these things are in place, the circuit can be scaled up to the low MHz range and hundreds of kilowatts without any major challenges, but it does add enough complexity to make voltage fed half bridge inverters look attractive again.

[NyaaX_X]

Thank you Anders !!
Sorry for I don't really understand that how to make that RC delay overlap. I edit my draft a little bit. I find that seems MOSFETs have a lot power loss. And the sampling waveform for IC driver signal in are each of MOSFETs Vds. The duty cycle of it are less then 50%... Anyway I'll post the screenshots of simulation here. And hope the problems can be resolved

Ps. The working frequency in the simulation is about 500kHz it can push up to 2.5MHz but the MOSFETs power loss turn huge. And if it run under low frequency like tens of kHz it Vgs and mosfets power loss are also bad. I think the sampling capacitors (in the image are those 1nF capacitors) need tuning for different frequency. So...

###########
ZVS 230910.zip
###########







Main inductor waveforms

[tarak]

hi  have you tried driving it with the SG3525 ?

[NyaaX_X]

No I have not dirven it with SG3525, the simulation is based on the original ZVS self-oscillator and add a gate driver IC to deal with the higher frrquency. Sadly I even did not make a real circuit of it and try if it works.

I watched someone use 3525 to make that for tesla coil V-bus power on youtube but it seens that is not a self-oscillate one.