Yes. Unless "best" is very well defined with specific goals and requirements, then it has no meaning.
I'm no expert at all, but I can say that circlotron topology can do without a coupling cap on the output.
Sheldon
Because no suggestion come here at today, in these days i have simulate a circuit with transformers as the only voltage gain element. Thinking about a scheme without caps on the signal path and not use of complementair pair, i have drawn the following schematic in the attached file.
Your comment and proposal are welcome.
Francesco
Your comment and proposal are welcome.
Francesco
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I've often thought about doing similar, but single ended. That means adding a capacitor or two, but it would also reduce overall circuit complexity. Perhaps that would be a good compromise. I think I will build one as a winter project.
Did you do a simulation? Looks interesting. I would think that a transformer with adequate primary inductance would have high enough DCR to keep the bias current for the input pair quite low.
Sheldon
Sheldon
Single ended was my first choice, but since the signal transformer on the market not allows dc current
, then is necessary parallel feed through a big caps due to the little source (or RK, RE) resistance. Moreover single end output stage need another big capacitor for the load, only class A operation, and a little big output impedance relatively to push-pull stage.Previous, i have simulated same circuit as above attached, without the J308 front end, but due to the big caps of mosfet output stage the high frequency response was a bit compromised.
Francesco.
On the above sentence, it must be added here that for a step-up transformer, the secondary impedance is high, so then with the input capacitance of mosfets, it can realize a pass-bass filter that will be avoided.
Francesco
Yes, i am agree.
We can select jfets for different idss and Vgsth so we can manage the primary transformer input resistance to accomodate it.
My circuit is as one example, other similar devices can be employed, also Vfets.
Simulation in hard to be right, if we not have the model parameter about the transformer.
Francesco.
Single ended was my first choice, but since the signal transformer on the market not allows dc current
I don't understand what you plan to do then. Your schematic shows two separate single ended transformers, with the output wired in opposite polarity on one side. OK, that will act as a phase splitter, but that means DC current in the primary.
Sheldon
Hi Sheldon, thank for your observation My simulator not have a specific transformer with two windings on the primary and two windings on the secondary, so i have placed two equal single winding transfomers connected as a single ones with twice windings for each side. Then, as you see, the dc current in each input jfet run in opposite mode through the two primaries windings and act a dc cancellation, if the two currents are the same. In this way not are need a capacitor as you know.
Francesco.
Yes, a simulation with two single winding transformers for side not are the same as a real PP transformer and it deceive me. Sorry.
As its connected in the above diagram, there is dc, but also ac cancellation, through the two primaries. Here it need different arrangement as in the below version 2.
I hope this should be right. Francesco
If we find all matched complementair pairs we can make a more easy circuit as the following:
Francesco
Francesco
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Both. You already explained yourself, why V2 won't work. V3 won't work for the same reason. You will either have DC in the core, or your AC will cancel. Draw up the current flows and AC response to AC input.
Sheldon
These transformers are a big traps!!!
Before all, are you agree that in version 2 and 3 there is dc mutual cancellation?
Then, as i think, i explain because not there is ac cancellation instead.
as yo can view, when applied a positive impulse, the current in the top N-jfet (therefore in the top winding) rise up, meanwhile in the bottom P-jfet, (therefore in bottom winding) go down. Either fets are wired with the fase + on each winding, so i not see AC current cancellation.
Francesco.
Francesco.
If you wire the transformer so that AC current is not canceled, then DC current is not canceled.
Draw a diagram with just the input transistors and primary windings. But arrange them side by side. It's easier to see that way. If the DC current goes in opposite directions, then as current in one winding increases, current in the other winding decreases. The core sees no net change.
Sheldon
On second thought, I see what you are trying to do now. Yes, with a negative rail you can arrange the primaries to cancel the standing current, and swing with a single input polarity. So, in principle, it should work. But is it practical?
I'm no transformer expert at all, but it may not be so easy to get something off the shelf that performs well.
Sheldon
I'm no transformer expert at all, but it may not be so easy to get something off the shelf that performs well.
Sheldon
This afternoon i tought the same idea. PushPull operation happens between the two primary coil, but the secondary not see energy since the magnetic flux generates by either primary stay constant. Instead it happens, if one jfet input is put to ground.
My error was to see (look to the image) as two separate magnetic flux, meanwhile we think about one single PP transformer with only one magnetic flux generated by one iron circuit.
Is't so difficult to find a good follower schematic to drive well the transformers ?
I ask me if this difficulty has forced others guys to begin with transfomers in their circuit ?
Let me think about.
Francesco
Very simply. It is physics, nature laws)
Read the theory of transformers. It is written so a long time.
Problem in optimisation peak-to-peak value - an induction-inductance of coils - capacity of coils. Excellence calculation Is required. I.e. calculation of such transformer is nontrivial, unusual to the accepted calculation. If you know the theory of transformers and have experience of self-maintained calculation and manufacture, try to count similar "the transformer - the voltage amplifier" with an impedance of a loading for a secondary coil 4000 Ohm and a current 5 mA, coefficient of amplification 8. There will be many problems and major weight of the transformer)
Here :
http://translate.google.com/transla...nes/FS.htm&sl=ru&tl=en&history_state0=&swap=1
I tell about such the device of such transformer and I offer self-acting calculation for "the transformer - the voltage amplifier" for my amplifier. But manufacture of such transformer nonconventionally. You should fathom it. Though also this amplifier also is unusual, nonconventionally builted). Naturally as everything, that I make😉 - including a lot of unusual in construction topology
"The transformer - the voltage amplifier" as the basic device is interesting only to transistor circuits. In vacuum-tube circuit designs, the truth, always used very small, correcting coefficients of amplification of voltage on transformers because high capacities of coils with a major impedance badly transmitted a wide frequency gamut. I like to use for tubes coefficient no more than two, sometimes it "recovers" sounding.
I English is very bad, unfortunately. I hope to you clearly, that I speak)
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