Wireless Mains Adapter-Frequency etc.?

[Skywave]

Thanks Al,
What about my Fets IRF2807?
Mike

Hi Mike.
I see that we are on post #50 with this thread now . . . it's all getting a bit confusing. Please explain what, exactly, you wish to know about your FETs in this application? I'll help if I can.

Al.

[pwdrive]

From an article:

""I have to confess a marked objection to the various statements sometimes seen that the reactances "cancel out". The reactances are not sentient beings! Coils and capacitors do not sit and conspire together to reduce their reactances to zero as the resonant frequency is approached! The reactances within each of the components are still very much present at resonance as is the relative phase difference due to them (if you were to take the components out of the circuit and measure their individual reactances at that same frequency you would see it) but the net phase difference across the input terminals becomes zero because phase differences, unlike reactances, do cancel and all the generator sees is a pure resistance. Hence the conjugate impedance required of the generator to get the most power into the load is also a pure resistance. As we saw in the paragraph above, a reactive load must be driven by a reactive generator having a conjugate impedance, and a vital consequence of the maximum power theorem is therefore demonstrated by tuned circuits themselves""

Full article below:

http://home.freeuk.net/dunckx/wireless/m...ower1.html

Lawrence.

[Skywave]

Quote: "At resonance, the reactances cancel out".
Strictly speaking, yes, that is incorrect. But make a small amendment to that sentence: "At resonance, the resultant effect of the reactances is to cancel each other out", then I cannot see why that should be objected to.

The subtle difference is that in the original statement an electrical property is referred to; in the amendment, it is the effect of that property that is referred to. But, overall, I consider that the author is hair-splitting and being pedantic. As I stated in an earlier post, it is all a question of phase.

Al. / June 12, 2013 //

[pwdrive]

I think the author in that article was maybe making a reference to the "reactances cancelling out" being often misinterpreted as that the reactances somehow disappear, which they can't as both L and C are reactors by their very nature when fed by an AC source weather oscillating or not, as I understand it.

Lawrence.

[boiss]

Ok Al,
I attach the waveforms for gate, drain and output.
I tried a new the 18 Turn coil and there was a reduction in the heat of the coil, now about 60C. I also wound an oval coil, this with a few changes into a semi bone shape
works quite well but the standing current (No Load) is very high around 2A.
I tried different combinations of C etc with frequencies up to 500KHz but the output is very low and the Fets get hot.
The heat is the killer here with all these options, I can't sit the radio over something putting out 20W of heat.
At the end of the day I reckon I will have to be content to charge the batteries at 50- 100mA and not run the Radio from the "Adapter"
I have no experience of Fets and their biasing etc, the waveforms are gate 10V pp (limited by the 10V Zener) and Drain 60V pp. Note the ringing on both waveforms.
Any enlightenment re using FETs would be most welcome.
Mike

[Skywave]

O.K., thanks Mike. Can you now present the cct. diag. please? Then, hopefully, we can get a better understanding of what is going on.

Al. / June 12 //

[Refugee]

I have just had a quick look at the data sheet for an IRF840 and they work like a valve with the gate voltage between 4 volts and 6 volts with an amplification that is huge at about 5 amps per volt.

[Skywave]

I have just had a quick look at the data sheet for an IRF840 . . .

Why the datasheet for the IRF840? In post #50, Mike clearly states that he is using IRF2807. Moreover, the specifications for those two devices are quite different!

Al.

[Refugee]

Only just a quick look at one. I happened to be able to look taking the number from memory without going all the way back.
The IRF1807 just does even more amps per volt.
We are only looking in general at the way they differ from valves.

[Skywave]

We are only looking in general at the way they [IRF FETs] differ from valves.

"We"? You may be, but how does the spec. of power FETs - as compared to that of valves - help Mike get his cct. to work as he requires? Mike has provided some waveforms and performance data using his FETs and I have asked him to provide the cct. diagram of his prototype. Surely that is the type of information that will be helpful to us all here, and, in return, we might be able to help Mike.

Al.