My NON-discrete SODFA class-D amp

[analogspiceman]

Alright, over the holidays I've been able to try out different topologies (UcD, SODFA, hys. osc.) and have acquainted myself with RightMark Audio Analyzer (RMAA) which allows for frequency response, THD, IMD, S/N, etc. measurements using your PC equipped with a good quality sound card.

[cut measurements]

Obviously you'll need to subtract the THD for the soundcard from the total THD which yields the following results:

SODFA THD+N(A) = 0.033%
UcD THD+N(A) = 0.030%
Hys. osc. THD+N(A) = 0.012%

What's obvious from these results is that my output filter has a high-Q which isn't compensated for by the SODFA and hys. osc. that have pre-filter feedback, the UcD (with post-filter feedback) does a good job of keeping the output filter in check. What's also clear is that THD results are respectable for a breadboard-amplifier, but that the SODFA and UcD have comparable THD results. The hys. osc. clearly has the advantage here.

Any feedback, comments or suggestions are most welcome!

Hi Sander,

I took a look at the LTspice file you sent me.  You mentioned that it was of the breadboard amp that got the best results, so I must admit to being a little confused, since I would describe the self-oscillating amplifier in the schematic you sent me as of the pre-filter, negative feedback, phase-shift type.  Positive feedback is a defining requirement for a hysteresis based self-oscillating amplifier.

The simulation shows what I would consider unacceptable cross-conduction.  Per your request, I have "improved" it and will email to you shortly.  The level shifters now include deadtime generation and the driver output now has active turn-off assist.  I didn't bother changing it, but since your output filter is outside the feedback loop you might want to increase the value of the damper capacitor.  Layout issues are another matter altogether.

You inadvertently did not include the various model and library files needed to run the simulation.  I had some of the models and improvised for the others, so you may need to adjust the deadtime to suit your target mosfets.

Regards -- analogspiceman

 

[Pierre]

Yes, the THD originates from the soundcard; if I take the amplifier out of the loop the 0.008% is the THD result. Hence anything above that 0.008% is generated by the amplifier.

Yes, I agree, but that doesn't mean that you can calculate the distortion introduced by the amplifier simply by substracting that THD level from the reading. Or at least I don't see it so clear.

 

[Elias Novaes]

hi sander.... is possibile to make one upgrade in this project to obtain high power ? example : bridge with 2kw rms.

sds

 

[umut1001]

hi about ir

hi..i have 4 pieces of ir 2110 ..and i want to build a fullbridge amplifier more than 250 watts of rms and 20-20khz bw..can anyone help me

 

[TOINO]

Hi.
This one is based on Crest LT, but bridged.
It seems complicated but it works.
They are not dead time adjustment because of the “special arrangement” (patented by Peavey and others):

Page 5
http://www.freepatentsonline.com/4724396.pdf

http://www.freepatentsonline.com/5117198.pdf

http://www.freepatentsonline.com/5946208.pdf

Page 3
http://www.freepatentsonline.com/6992527.pdf




If you need a simpler one (just for sub) see page 7 of this link http://www.yorkville.com/downloads/servman/smls800p.pdf

 

[Pierre]

Wow! What frequency do that ones run at (The Crest LT and the Yorkville one)?

 

[TOINO]

About 300KHz for the Crest. This is critical because of L1//L4 values that must be optimised for the carrier frequency.
Yorkville I don’t know. I estimate that must be low because of 100ohm gate resistors.
Anyway I think the important here is only the gate driver IC connection as a guide for umut1001.

 

[umut1001]

thanks toino

thank you toino..i dont know i can buil it.i hope i can do..but i didnt decide to make a self oscillating pwm circuit..is it better than using triangle oscillator?.there are several techniques..but i dont have much time..i will build it for graudating university project..if you get more simple circuit please send me..best wishes...

 

[Pierre]

For the yorkville, I have seen that the triangle waveform is produced by a 555 oscillator. From the components shown, it seems that the switching frequency is only around 4 KHz!!!!

 

[luka]

Hi

They sure don't run at 4kHz

 

[Pierre]

Sorry, I have reviewed my calculations and the Yorkville seems to switch at 70KHz.
The oscillator is U8, a 555 in astable multivibrator mode (resistors are both 1K, but the timing cap is C32, 6n8, while I had taken C80, 100nF, that is only a bypass cap).
(The sawtooth is not symmetrical at all, however: 9.4us vs 4.7us) I suppose that's compensated by feedback.

 

[luka]

Hi

Thats much much better

 

[TOINO]

Voilà Pierre

And now friends?... should we help umut1001?

 

[umut1001]

hi ..ir2110 fullbridge

hi everybody..i bought many ir2110 ,1n4148 ,1n4007 ,bc546 and uf4007(ultra fast diode)..and i found a good and cheap toroid transformer but i didnt buy it yet..it is 60usa dollars ..made in italy and 33.6volts 16 amperes and..it makes 47 volt dc..can i make a 250 watts of amplifier with that transformer?i think i can use 2 ohms load..and i want to buy lm311 or lm319 ..i do not know which one i prefer?i want to use lt1016 but i couldnt find lt1016 for comparating opamp..thanks

 

[luka]

Hi SSassen

I see that you have some kind of power calculator for LTSpice, could you send me one?

 

[kees52]

Alright, some more cool scope photos. This time around I followed a different line of reasoning, as when you're trying to limit overshoot at the output, who says that overshoot wasn't present on the input to begin with? So in this case you'd better try to fight the cause rather than the effect. Please refer to the below URL of the schematic these comments are in reference to:

SODFA class-D amplifier, revision 007
http://hardwareanalysis.com/images/...large/11666.gif

Overshoot comparator output

The above image shows what signal the IR2011 MOSFET driver is fed with on pins 5 and 6. It is clear that there's a fair amount of, undesired, overshoot here which we need to get rid off, or at least minimize.

Overshoot integrator output

The above image clearly shows that the integrator itself, 1/2 of the OPA2134, outputs quite some overshoot at pin 7. So what we're looking at here is overshoot that's introduced at an early stage in the amplifier and simply propagates throughout it. This could be crosstalk from the output section of course. For now I'm a bit puzzled on how to reduce or remove the overshoot at the comparator output or whether it is crosstalk or something generated in the amp itself.

Any helpful suggestions are most welcome!

Best regards,

Sander Sassen
Hardware Analysis - Computer hardware news, reviews and forums that provide help and assistance with problems.

Looks nice, I mean as a transmitter, class D are nice transmitters when do not pay attention about the demodulator coil.

 

[SSassen]

C'mon, are you kidding me? This was a design I did almost 10 years ago (!) with a prototype on perforated board, on a proper double sided PCB this design shows much better behavior. The perforated board prototype was just a proof of concept.

 

[stewin]

hi ssassen please post pictures of your improved class d amp layout

 

[SSassen]

hi ssassen please post pictures of your improved class d amp layout

You did notice when the initial posts were made yes?

 

[kees52]

I do see oscillations in the risetimes, or heavenly ringing or maybe shoot through?