well, it should work at +-80v ...
the real problem is the mosfet: i have no source for the real "nice" fets, like philips PHP28NQ15 ...so i used irf640n. and here are the problems !
Cg too much, back diode slow >> too much idle current + too slow switching at high supply.
maybe i try with harder gate-drive, but i made a smd-board, so not much space for bigger driver. or i get "better" mosfets...
the real problem is the mosfet: i have no source for the real "nice" fets, like philips PHP28NQ15 ...so i used irf640n. and here are the problems !
Cg too much, back diode slow >> too much idle current + too slow switching at high supply.
maybe i try with harder gate-drive, but i made a smd-board, so not much space for bigger driver. or i get "better" mosfets...
ok, right, but you never know, if you dont try...
or with other words: in swcad simu running fine, (nobody told me, that the mosfet models are sh.. , only "guru" bruno wrote, he dont use simu, because real life is too different) , real amp fine , but at 40v and up, real amp is no more like simu !
in test: without mosfet, but with 10nf load for the driver switching is ok.
so i wonder: irf640 at +-70v shows much more "nf" Cg !!??
or i have a bad magnetic effect, that slows down the driver...
you could see it here:
d-amp
or with other words: in swcad simu running fine, (nobody told me, that the mosfet models are sh.. , only "guru" bruno wrote, he dont use simu, because real life is too different) , real amp fine , but at 40v and up, real amp is no more like simu !
in test: without mosfet, but with 10nf load for the driver switching is ok.
so i wonder: irf640 at +-70v shows much more "nf" Cg !!??
or i have a bad magnetic effect, that slows down the driver...
you could see it here:
d-amp
With this it goes right back to the loading of the comparator stage/current source.
Output current gets higher and higher, all transistors suffering miller effect (down to the current mirrors) get weighed down more and more by it.
Any point along the chain you can minimize this effect should likely be taken.
There's also all kinds of other aspects that come into greater play because of all the higher currents running around, they're likely to require snubbing/control at higher power.
The use of the cascaded output stage on the comparator does alot to even things out and make it less susceptible to the miller current slewing around. It will also help ensure equal temperature of the mirror transistors. That's the reason for them.
Even fokkers basic fumbling with gate driver IC's is only good up to a certain power level before you have to know what you're doing.
You can still use the simulator as a baseline, if you design drivers with the right properties it's quick to check basic operation with a simulator, final values will have to come from real world teaking.
There's other factors why this amp isn't as good as even the more basic DIY versions.... which are more Hypex like in implementation using fully differential feedback etc.
It would have been cool to have heard more about your efforts with this, is it still a work in progress?
Ahh yes, I had seen that, but did not follow because it's not my language.
Output current gets higher and higher, all transistors suffering miller effect (down to the current mirrors) get weighed down more and more by it.
Any point along the chain you can minimize this effect should likely be taken.
There's also all kinds of other aspects that come into greater play because of all the higher currents running around, they're likely to require snubbing/control at higher power.
The use of the cascaded output stage on the comparator does alot to even things out and make it less susceptible to the miller current slewing around. It will also help ensure equal temperature of the mirror transistors. That's the reason for them.
Even fokkers basic fumbling with gate driver IC's is only good up to a certain power level before you have to know what you're doing.
You can still use the simulator as a baseline, if you design drivers with the right properties it's quick to check basic operation with a simulator, final values will have to come from real world teaking.
There's other factors why this amp isn't as good as even the more basic DIY versions.... which are more Hypex like in implementation using fully differential feedback etc.
It would have been cool to have heard more about your efforts with this, is it still a work in progress?
Ahh yes, I had seen that, but did not follow because it's not my language.
fokker said:
dear fokker (and others)
months ago, I think you have seen my earlier post(s), about my D-amp, the UCD way... I 1st started out a circuit something VERY SIMILAR (note something VERY) to the philips app note....It worked even with BAD component selections, then after some parts swapping and some circuit simulation and some PMs from experts and the inventor himself, I tried it with the cascode type / 2 transistor current source...
ALL did it in a few months time, swapping/simulating/guidance from experts.. until I finally settled with optimized components...
I AM ONLY using IRF540 because it is the best part that I could find here in our place... got no extra money to order those "nicer" parts.. too bad.. but at least, THIS PROVES that even with "less than nicer parts", you can stil have quality amp.... I have junked my 100W AB amp, in favor of my diy UCD....
Classd4sure(Chris) has ALREADY posted his running schematics and with some changing of parts from sim to real world, IT HAS WORKED! I have NOT deviated from that circuit since, just tweaked values... I just added some extra features (like over voltage protection)... got it here in THESE forum... and the over current protection?? I had an idea how to but was not sure how to implement it....had to do some simulations again(and some help from Bruno himself, thanks bruno)... so there!!
Lets all do our share in "learning" .... all info is out there, waiting to be understood and learned....This is a forum where you can choose to build or not to...
SORRY, but im not showing/releasing my selection/parts optimized, w/c I have learned in a few months time... that would be unfair on my part (not unless I get paid??
) .. there is really NO OTHER option but to (build it) and learn...there is no KIT for it either... In those few months , I came close to understanding how a UCD works I might NOT be an expert/or an engineer, BUT I can 9and DID) learn...BUILD the circuit from what chris has posted (and me).. I have posted what I have been using in my thread .... believe me, it WILL WORK!! just post your results and we could hopefully help you out...
-simulate- and build.... and learn... trust me, its FUN!!
Im curently making MY OWN -modulator- PCB... for a more nicer look... its DONE already but have not transfered it yet to board....
hope this clears up a bit...peace
Regards,
Raff
Raff,
I think part of the obvious difference is you went into it willing to learn /try /research, get your hands dirty and you were willing to accept even cryptic advice and made the effort to decipher it.
Can't have it all handed to you and if you did you wouldnt' have learnt. You'd be stuck with an amp that kind of sort of half works and wouldnt 'know what to do with it, then when you're fed up of swapping parts aimlessly without knowing what they're doing or why they're doing it, you'd be here picking bones, moaning about all the "experts" who dont' really know anything.
Can't please them all you know. Great idea to keep your final schematic personal, you worked hard enough for it, and anyway, people just use whatever parts they have around anyway, and then wonder why the values you've shown them don't work with their transistors.
There's only a dozen links and more schematics around here already that fully discuss the issue, long before the existance of the philips application note.
+- 55 hm..... I think I see a challenge
I think part of the obvious difference is you went into it willing to learn /try /research, get your hands dirty and you were willing to accept even cryptic advice and made the effort to decipher it.
Can't have it all handed to you and if you did you wouldnt' have learnt. You'd be stuck with an amp that kind of sort of half works and wouldnt 'know what to do with it, then when you're fed up of swapping parts aimlessly without knowing what they're doing or why they're doing it, you'd be here picking bones, moaning about all the "experts" who dont' really know anything.
Can't please them all you know. Great idea to keep your final schematic personal, you worked hard enough for it, and anyway, people just use whatever parts they have around anyway, and then wonder why the values you've shown them don't work with their transistors.
There's only a dozen links and more schematics around here already that fully discuss the issue, long before the existance of the philips application note.
+- 55 hm..... I think I see a challenge
I'd say you're plain wrong and have quite some nerve stating that, if there's someone that deserves to be padded on the back and complimented on all his work with a UcD style class-D amplifier then it is Chris. Esp. considering all people he's helped making their first endeavours into DIY class-D amplifiers, or understanding how they work in general.
Quite the opposite to be honest, given the fact that all Chris had to work with is his simulator and a box of parts. He managed to get a UcD amplifier up and running, built from scratch using run of the mill components without the luxuries many of us take for granted such as a ocilloscope.
And what did you build exactly?
Best regards,
Sander Sassen
Positively not RoHS compatible
Hey Sander,
Thanks.
I'm not all that bothered by him, feels like a gnat gnawing on my ankles is all.
You know what I still have that homebrew sucker in a semi working state... just needs a few caps that I borrowed for something.
Since I finally have a scope now, as soon as I make some probes and such..... I can't wait to throw that ol thing on the scope and see how frightening it is!!
I'll do all I can to get some pics of the gate waves from it and throw them up here so we may all laugh
BTW I never would have gotten as far as I did with it without Bruno's help!
and many others like Charles Ivan Johan and I just like to give back a little.
Cheers
Thanks.
I'm not all that bothered by him, feels like a gnat gnawing on my ankles is all.
You know what I still have that homebrew sucker in a semi working state... just needs a few caps that I borrowed for something.
Since I finally have a scope now, as soon as I make some probes and such..... I can't wait to throw that ol thing on the scope and see how frightening it is!!
I'll do all I can to get some pics of the gate waves from it and throw them up here so we may all laugh
BTW I never would have gotten as far as I did with it without Bruno's help!
and many others like Charles Ivan Johan and I just like to give back a little.Cheers
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