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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Hello Plasmaddict,
Yes I know something about resonant converters, but I as yet have no practical experience with them.
Here are my main questions:
(1) Generally speaking, as far as most people on this forum would likely be concerned, what's the main reason for using a resonant converter over another type?
(2) Are there any load conditions that would cause it to to go from soft to hard switching, e.g., heavy loading causing a low "Q"?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
jpsmith123 wrote ...
Here are my main questions:
(1) Generally speaking, as far as most people on this forum would likely be concerned, what's the main reason for using a resonant converter over another type?
The main reason is soft-switching, which practically eliminates switching losses (switching losses usually dominate conduction losses in hard-switching converters).
There are other types of resonant converters (current fed parallel resonant converter is the only type I am aware of) which can take the reactive current away from switches into the LC circuit, this drastically decreases their heating. This is very useful for driving highly-inductive loads such as transformers for capacitor charging / Jacob's ladder or other uses where you need current limited output. This technology is especially useful for high to very high powers where you don't want to use large expensive devices.
jpsmith123 wrote ...
(2) Are there any load conditions that would cause it to to go from soft to hard switching, e.g., heavy loading causing a low "Q"?
With the SLR converter? I think so, with light loads or open circuit, hard switching can happen. If you design your transformer well (as I said - low leakage and use external inductance), the switching losses can be minimised.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
As I understand it, depending on circumstances, what you gain in reduced switching losses might be offset, to a certain extent, by higher conduction losses.
In any case, I'm not sure I see why there should be a difference (as far as the transistors are concerned) between the use of an external inductor, or the use of an exaggerated, transformer-inherent leakage inductance...seems to me the transistors will pay a price regardless.
Anyway, I hope to try and simulate a resonant converter one of these days, to get an idea of how they behave, before I try to build anything.
BTW, has anyone been able to simulate the so-called "Mazzilli driver"?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
jpsmith123 wrote ...
As I understand it, depending on circumstances, what you gain in reduced switching losses might be offset, to a certain extent, by higher conduction losses.
No, the conduction losses stay nearly the same, so the overall dissipation is greatly reduced.
jpsmith123 wrote ...
In any case, I'm not sure I see why there should be a difference (as far as the transistors are concerned) between the use of an external inductor, or the use of an exaggerated, transformer-inherent leakage inductance...seems to me the transistors will pay a price regardless.
I also don't know.. but ask Steve Ward
jpsmith123 wrote ...
BTW, has anyone been able to simulate the so-called "Mazzilli driver"?
I simulate circuits in my head but the "Mazzilli driver" is a push-pull type of current-fed parallel resonant inverter. These inverters have very low losses on the switches but core losses may be increased. Some day I am going to build a half-bridge CPFR inverter, but I don't have any large cores right now so it won't be of any use until I get some core(s)...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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@Bernie: That looks like what I want to do. I've already tried quickly with another simulator, "CircuitMaker 2000", but it didn't seem to work. I'll fool with it a little more and then I'll d/l LTspice and try that.
BTW, if I may offer some constructive criticism of your model, it looks to me like your primary inductances and coupling coefficients are unrealistically low.
@Plasmaddict, I'm glad for you that you can simulate things in your head. However, being that PCs have become so powerful and cheap, and simulators so readily available, I generally find it saves time, money, and aggravation, to putz around a little bit beforehand with virtual parts.
For example, Berni's "Mazzilli driver" model may provide some clues as to why you experienced the troubles you mentioned in the "'zvs' flyback driver on mains?" thread here:
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
jpsmith123 wrote ...
For example, Berni's "Mazzilli driver" model may provide some clues as to why you experienced the troubles you mentioned in the "'zvs' flyback driver on mains?" thread here:
I don't think the simulation includes things like gate capacitance, gate threshold voltage, transconductance and transfer characteristics of the MOSFETs etc. (maybe I'm wrong here?) Anyway if you actually build that circuit you will see there's little ringing on the primary waveform. Btw. I have already solved my problem in that thread but anyway I don't want to get too far off topic here...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Yes, the models generally do account for those things...otherwise the simulation would be not very helpful.
Did you actually solve the problem you mentioned, i.e., you were able to make a "Mazzilli driver" work off the mains (if I understood you correctly), or you found a "work around" solution using a different type of circuit?
Registered Member #1132
Joined: Mon Nov 19 2007, 06:15PM
Location: Slovenia
Posts: 84
Oh and about running it off mains, in the simulator even when run at 24V the cirucit went nuts.
Btw i highly recomend useing switcher cad since it is a very acurate and capable simulator, its just a bit harder to use.Oh and this simulator was first developed to simulate switchmode powersuplys, that means it has exelent models of inductors and trasnformer but also exelent models for mosfets and simalar things.
If you want to run it off mains why not makeing a half H bridge and a 555 timer driveing them.Get some 1200V IGBTs and you can run voltage doubled mains in to it thats 650V! And if thats not aough for you you can make a full H bridge so that means 1300V of input to your transformer.Then you only need like a 1:10 thurn ratio to already get some HV.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
jpsmith123 wrote ...
Did you actually solve the problem you mentioned, i.e., you were able to make a "Mazzilli driver" work off the mains (if I understood you correctly), or you found a "work around" solution using a different type of circuit?
The problem was the feedback - I used a voltage sense winding on the transformer core to drive a pair of TC4422 gate drivers. The parasitic oscillation problem went away. I actually ran it fro 110VDC so far but there were not any problems, I can imagine running it with full rectified mains just fine.
There is also a possibility to make this circuit into a half-bridge, then you only need devices rated at pi/2 times the supply voltage (but you need a dual-winding choke).
If I ever manage to get a bigass ferrite core, the half-bridge CFPR inverter will be my choice for driving it.
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Methods of Winding Large Ferrite Cores
but the "Mazzilli driver" is a push-pull type of current-fed parallel resonant inverter. These inverters have very low losses on the switches but core losses may be increased. Some day I am going to build a half-bridge CPFR inverter, but I don't have any large cores right now so it won't be of any use until I get some core(s)...
but anyway I don't want to get too far off topic here...