Just for the hell of it I decided to post this today. It's a little brainwr eck of mine. I have looked around enough that I THINK it is unpatentable bu t I THINK it is a different implementation than usual, or at least I haven' t seen it.
I have flippantly or lovingly (take your pick) dubbed it the "Class T" ampl ifier for reasons beyond the scope of this text. (details available on requ est)
One thing not shown there is the line from the power oscillator to the driv e circuit which is needed to sync it. The idea is not complicated, the tria c is triggerred just before zero crossing. The oscillator runs at about 60 Khz or so to facilitate use for the audio spectrum.
To drive positive, the trigger pulse during that phase is advanced with res pect to the output of T1. To trigger negative of course the trigger is adva nced before the input power switches back to positive.
In the waaay back burner of my mind is the drive circuitry. I would like to implement it totally in the analog domain. Basically a ramp generator and comparators or something along those lines. Sample and hold of course, I gu ess it would be a good idea to do that at the power oscillator frequency eh ?
I think I can make this thing even cheaper, but for certain applications. F or example a powered subwoofer. If you adhere to proper design for a "hot" ground, T1 could be elimintated and the squarewaves from the oscillator cou ld be fed directly to Q1. For triggering, optocouplers could be used with w hatever circuitry (surely doable)and we're down to three power devices, not a one of them spending a microsecond dissipating, a coil and a few capacit ors. The cap up there coupling into T1 would feed Q1 directly but would hav e to be large enough to bypass the lowest frequency to be amplified. The wh ole thing would be easier to design with T1, but if push came to shove it c ould go, and then the whole thing needs to be isolated. If it's an amplifie d speaker, that would entail satisfying the UL or whoever regarding the enc losure. Still doable.
I could see this as useful for sound reinforcement, like bands on the run s etting up at different venues. The amplified speakers do eliminate another thing for the roadies to carry. The cabinet would have to be ruggedized jus t to make it safe, as internally the components would have path and potenti al to earth. But it could be done that way.
In this case, like with most (audio) power amps, I think it would be a wast e of time to try to regulate the power oscillator. The only efficient way t o do that is by running it above resonance and controlling the frequency. T his would cause complication in the drive circuit I think, and believe that a constant frequency is very desirable. Also, that matters in the choosing of L1 and C2.
Down there, C1 and R1,2 are to assure the triac turns off on time. The resi stance is there strictly to keep the peak currents down, and there are two because I think that R1,2 opening would not be a really desirable failure m ode. In fact detecting that for a shutdown would be good, but let's make it work first before figuring out how to make it stop... (one of my sayings, number 23 I think, I could look it up if you insist)
I'm pretty sure this is unpatentable because there is enough of this going on in directly fed VFDs for motors. Instead of plunking down the hundred bu cks for a provisional, I looked and found there are VFDs that do not even b other to rectify the AC. They run on three phase and convert frequency with triacs. Actually I was kinda impressed, and the thing is super efficient. I state now though, that those VFDs were not the inspiration for this, I ha d no idea such a cicuit existed until I actually looked, as I was wondering if this "Class T" doodad was worth the hundred. Once I saw that I figured that if someone hadn't done it yet, they coud easily enough, so it would be somewhat like trying to patent the wheel.
Of course when corporate gets through, they WILL patent the wheel and anyth ing that rolls is going to generate a royalty for them. Look man, I live in the US and every time I say "Now I've seen everything" they come up with m ore shit, especially in law. That is also beyond the scope of this text bec ause it would be a BODY of text akin to the works of Hamurabi. You folks in the good countries have no idea of the crazy shit that is illegal here.
Anyway, I guess it goes without saying that I submit this figuring someone will at least comment. You might call me a madman, but remember Madman Munt z ? People could not believe his TV worked with so few tubes. Now I have an amp with only one output device per channel, but not that old inefficient class A, and it can't really be called class B, or AB. It is certainly not a conventional class D, and it certainly isn't class G or H.
Thus - class T.