classd4sure said:
I would think the short life expectancy would be a big problem if the LED is driven near its maximum current rating. Maybe they have a problem of needing to be driven so hard to function well. But even the 6N137, the fastest most common one I have suffers from a propagation delay of over 100ns IIRC--not a big problem for a high power sub amp though. "There you (I) go again."
I had a chance to look up the 6N137. The Fairchild datasheet lists a typ. prop delay of 45ns, max 100ns; rise time of 50ns; fall time of 12ns; pulse width distortion of 3ns, max 35ns. The rise time figure seems applicable to a 5 volt supply on the high end of a 350 ohm collector pull-up resistor. For 12v, plan on a 1000 ohm value of such a resistor.
Hi there,
My three ways are my subs I've abused them far too long on class A/B..In the end, the speakers won......the amp died.
Here is one very interesting implementation of a large duty pulse transformer, he even prototyped it on a cheapo plastic breadboard, and the real world results look pretty convincing to me, this could be a contender.
http://dsms.ajusd.org/~fritz/AN1.pdf
Fig 11, 14A, 17.
http://www.ixys.com/tmosign2.pdf
Ok.. Had another interesting one but it's vanished.
My three ways are my subs
I've abused them far too long on class A/B..In the end, the speakers won......the amp died. Here is one very interesting implementation of a large duty pulse transformer, he even prototyped it on a cheapo plastic breadboard, and the real world results look pretty convincing to me, this could be a contender.
http://dsms.ajusd.org/~fritz/AN1.pdf
Fig 11, 14A, 17.
http://www.ixys.com/tmosign2.pdf
Ok.. Had another interesting one but it's vanished.
Since the input of the two drivers can only swing between -35 and -25 volts approx proper gate-drive is automatically achieved with the drivers using a gain of 1.
I am not sure however if all simulators allow that the output of a voltage controlled voltage source can be referenced to any desired point (isn't that a nice high-side driver ?
).I didn't even have a close-enough look at the original patent. I just threw together a circuit with a comparator, an output filter and a "lead part" in the feedback. Since I am a fan of inverting designs it turned out inverting.
As to simulation results: Different simulators might simulate differently, so one has to tweak a little. And this counts not only for component values. In PSPICE the simulation parameter RELTOL has great influence. The lower, the more accurate (and usually nicer simulations) but the larger the chance that it can't converge.
BTW: you might have remarked that the gain in my circuit is only somethig below about 5. The circuit simulated nicer with lower (voltage-) gains, that's the reason why I chose it that low.
regards
Charles
Hi,
I possibly dont' understand how that source works at all. Seems like an odd place as it looks like it's on the wrong side of the source.
So I guessed right about why you're summing the feedback with the input instead of taking the difference....I impressed myself.
Anyway, I was wondering what the lower threshold of your input sensitivity was, about 100mV is the best I had.
Regards,
Chris
I possibly dont' understand how that source works at all. Seems like an odd place as it looks like it's on the wrong side of the source.
So I guessed right about why you're summing the feedback with the input instead of taking the difference....I impressed myself.
Anyway, I was wondering what the lower threshold of your input sensitivity was, about 100mV is the best I had.
Regards,
Chris
That's how mine simulates. Input signal is about 2 volts. You can see that I also have some offset. I don't think it would be worth to trim around the offset on the simulator. This should be done on a real life circuit. The switching residual is around 1 volt peak. If one wants lower then he has to lower the filter cutoff frequency or increase the switching frequency. Simulated THD is around 0.1 % with k2 dominating and much smaller k3. The rest is way below those two. While the absolute figures aren't that great (I didn't say that it is tweaked for optimum, did I ?), it is basically an optimal THD spectrum.
BTW: This time I used it in non-inverting mode.
Regards
Charles
P.S. if anyone likes to get the .SCH file, drop me a mail.
BTW: This time I used it in non-inverting mode.
Regards
Charles
P.S. if anyone likes to get the .SCH file, drop me a mail.
Attachments
In my opinion, it’s almost impossible to design a “correctly” functioning Class D OPS that meets EMC and Audio performance without the use of SMD components.
For best price / performance ratio in the 120W / 8Ohms power range, I find it better to use full bridge topology with Pch & Nch devices for the following reasons: -
Very simple / fast driver stage (but AC coupled – but so is any transformer solution). I would be concerned about guaranteeing start-up and overload “recovery” with any AC coupled solution – the FB integrator requires the correction operation of the overall Feedback-loop to establish its correct DC conditions.
Lower PSU rails say +/- 25V, which allows with care the use of 60V FET’s – with there inherently faster switching times and lower RdsOn.
Symmetrical +/-25V rails allows the use of cheap / high performance (low ESR) 35V electrolytic capacitors. It’s much harder to find good low ESR / low priced electrolytics above 35V.
Allows the use of “cheap” 50V SMD ceramic capacitors for HF decoupling.
Things fail with less “Bang” at lower voltages.
Cancellation of “Even” order distortions (but arguably, sonically this might not be the best thing), & PSU pumping – at 100W single-ended, this is an important issue.
Does not the feedback reduce the effects of PSU pumping? As the PSU rails increase, would not the feedback REDUCE the PWM modulation index to compensate for the INCREASING positive gain error of the OPS? (as the PWM modulation index reduces so will the PSU pumping) I have no experience of “hysteretic” type switchers – what happens to the switching frequency during “Pumping” – I’m guessing it reduces?
A well designed Pch / Nch output stage can switch at 1.5MHz (+/- 70mA quiescent current), with 5nS Hard deadtime and say a total of 25nS OPS propagation delay (maybe not an advantage with hysteresis switchers?).
When I look at my typical OPS designs, which while simple and cheap, use SMD components - which are not easy to source, and require good four layer PCB design skills – none of which meets the DIY constructors requirements.
The best performance 60V MOSFET’s I’ve found and used to date are: -
Vishay – Siliconix’s
SUD10P06-280L
SUD15N06-90L
Si7414DN
Si7415DN
Fairchild
FDD 5612
FDD 5614P
The Vishay – Siliconix’s devices being the best switchers. For good high speed switching Toff Delay and D-G reverse Miller charge are the most important parameters.
John
For best price / performance ratio in the 120W / 8Ohms power range, I find it better to use full bridge topology with Pch & Nch devices for the following reasons: -
Very simple / fast driver stage (but AC coupled – but so is any transformer solution). I would be concerned about guaranteeing start-up and overload “recovery” with any AC coupled solution – the FB integrator requires the correction operation of the overall Feedback-loop to establish its correct DC conditions.
Lower PSU rails say +/- 25V, which allows with care the use of 60V FET’s – with there inherently faster switching times and lower RdsOn.
Symmetrical +/-25V rails allows the use of cheap / high performance (low ESR) 35V electrolytic capacitors. It’s much harder to find good low ESR / low priced electrolytics above 35V.
Allows the use of “cheap” 50V SMD ceramic capacitors for HF decoupling.
Things fail with less “Bang” at lower voltages.
Cancellation of “Even” order distortions (but arguably, sonically this might not be the best thing), & PSU pumping – at 100W single-ended, this is an important issue.
Does not the feedback reduce the effects of PSU pumping? As the PSU rails increase, would not the feedback REDUCE the PWM modulation index to compensate for the INCREASING positive gain error of the OPS? (as the PWM modulation index reduces so will the PSU pumping) I have no experience of “hysteretic” type switchers – what happens to the switching frequency during “Pumping” – I’m guessing it reduces?
A well designed Pch / Nch output stage can switch at 1.5MHz (+/- 70mA quiescent current), with 5nS Hard deadtime and say a total of 25nS OPS propagation delay (maybe not an advantage with hysteresis switchers?).
When I look at my typical OPS designs, which while simple and cheap, use SMD components - which are not easy to source, and require good four layer PCB design skills – none of which meets the DIY constructors requirements.
The best performance 60V MOSFET’s I’ve found and used to date are: -
Vishay – Siliconix’s
SUD10P06-280L
SUD15N06-90L
Si7414DN
Si7415DN
Fairchild
FDD 5612
FDD 5614P
The Vishay – Siliconix’s devices being the best switchers. For good high speed switching Toff Delay and D-G reverse Miller charge are the most important parameters.
John
That's not a problem at all if you add a parallel DC path.
According to Bruno it's not a good idea at all to use low ESR caps since they tend to increase ringing instead of reducing it.
But they do it in a less less interesting way (at least from a spectator's point of view
) !BTW: I tried to increase NFB by about a factor of five on my posted simulation example and it gave a significant reduction in THD and IMD.
Regards
Charles
phase_accurate said:
That's not a problem at all if you add a parallel DC path.
According to Bruno it's not a good idea at all to use low ESR caps since they tend to increase ringing instead of reducing it.
But they do it in a less less interesting way (at least from a spectator's point of view
BTW: I tried to increase NFB by about a factor of five on my posted simulation example and it gave a significant reduction in THD and IMD.
Regards
Charles
on your simulation, what's the DC bias point of the mosfets?
mines (based on your schematic) are dissipating more than 200W idle
Ouch
I didn't pay attention on this one (one nice feature of simulators: nothing explodes even when heavily abused !). I just took some restistor values for the gate-drive without any calculations. I have now decreased the discharging resistor to 1 Ohm and things improved (even THD !). This will still not be optimal (definitely not) but one has to play around with the values anyway.
One cannot talk of DC bias in this case - it is called crossconduction (or shoot through).
If your simulator takes the .sch files from Microsim I could mail you my one.
Regards
Charles
I didn't pay attention on this one (one nice feature of simulators: nothing explodes even when heavily abused !). I just took some restistor values for the gate-drive without any calculations. I have now decreased the discharging resistor to 1 Ohm and things improved (even THD !). This will still not be optimal (definitely not) but one has to play around with the values anyway.
One cannot talk of DC bias in this case - it is called crossconduction (or shoot through).
If your simulator takes the .sch files from Microsim I could mail you my one.
Regards
Charles
Hello,
Charles, looks good, lowest I got on mine so far is .2%....I was having many kilowatts shootthrough .....20K.......aaaaaaand....I've decided to abandone the pulse transformer Idea ..(for now) since I was obviously wrong about it not adding much complexity. I still think it would be most worthwhile attempting for an all out power design, but necessary? I doubt it.
So I'll fix my old circuit up a bit and redo what should have been redone a long time ago.
Last night my cable went out so just to kill some time I tried simulating an op amp based one with ideal switches, since I couldn't find a half decent comparator without google
It worked, very badly, but it worked.
I'll see what I can find for a decent comparator for it later on and play with that.
One thing I've noticed so far while alot of pspice's comparator/op amp models look like they have complimentary outputs, try to use them and you get an error, because they aren't modeled!
Chris
Charles, looks good, lowest I got on mine so far is .2%....I was having many kilowatts shootthrough .....20K.......aaaaaaand....I've decided to abandone the pulse transformer Idea ..(for now) since I was obviously wrong about it not adding much complexity. I still think it would be most worthwhile attempting for an all out power design, but necessary? I doubt it.
So I'll fix my old circuit up a bit and redo what should have been redone a long time ago.
Last night my cable went out so just to kill some time I tried simulating an op amp based one with ideal switches, since I couldn't find a half decent comparator without google
It worked, very badly, but it worked.
I'll see what I can find for a decent comparator for it later on and play with that.
One thing I've noticed so far while alot of pspice's comparator/op amp models look like they have complimentary outputs, try to use them and you get an error, because they aren't modeled!
Chris
Charles,
I just clued in to your circuit, even though it was explained to me..and mentioned several times..
I think I was spacing out terribly. "voltage controlled voltage source"....aaaaaaaahhhh
How did you go about playing with the gain of the loop without effecting the overall gain of the amplifier? Just a change in the RC portion of the loop?
Ok I'm back on the hunt for a comparator I can work with.
My thoughts on the H bridge, our reference amp should stay as simple as possible and cheap as possible, while striving for the best sound we can get out of it.
H bridges are far better, just not a requirement.
Why don't we keep it modular like Bruno had suggested, that way it remains an option for those willing to attempt it and spend the extra dime.
Chris
I just clued in to your circuit, even though it was explained to me..and mentioned several times..
I think I was spacing out terribly. "voltage controlled voltage source"....aaaaaaaahhhh
How did you go about playing with the gain of the loop without effecting the overall gain of the amplifier? Just a change in the RC portion of the loop?
Ok I'm back on the hunt for a comparator I can work with.
My thoughts on the H bridge, our reference amp should stay as simple as possible and cheap as possible, while striving for the best sound we can get out of it.
H bridges are far better, just not a requirement.
Why don't we keep it modular like Bruno had suggested, that way it remains an option for those willing to attempt it and spend the extra dime.
Chris
johanps said:Attached is a small (partial) schematic, intended as a more concrete proposal to stir up some more discussion. (It's embarrassingly incomplete, actually. )
But it does have a first order loop filter (noise shaper), a comparator, output mosfets+filter, and the feedback.
There's a template for a comparator, which should read LT1016 in the picture! That's a very fast comparator; perhaps too fast for our immediate needs, but it has nice complementary outputs. It does require +/-5V (or just +5V/0V), so it's a bit of a hazzle in that way too. If anyone has a another suggestion, feel free to share it...
Whether the output from the op-amp goes to + or - of the comparator depends on whether the following output drive circuit is inverting or not.
Assuming it's OK to use dual positive/negative supplies (Vdd, Vss) with GND in between, the issue is how to drive the mosfet gates, with suitable amplification and level shifting of the comparator output(s).
Chris (classd4sure) suggested AC-coupled gate driving, which would imply using P/N-fets instead of two N-fets. That's actually how I myself have done it before - but I would be very happy to come up with another solution with only N-fets and no AC-coupling on the mosfet gates.
Perhaps using an IR211x-like driver circuit, but with AC-coupled level shifting between the comparator output and the driver circuit?
Or a discrete driver solution similar to the one in the UcD-patent (again with some level shifting needed)?
Or am I completely lost? You tell me!
Hi,
Looks like the LT1016 you suggested could work fine.
There's also the AD790 (Thanks Bruno),
I like the looks of the Max9690
The LT1116 (Thanks Subwo1)
Probably many more.
I can't find any models!!!
Looks like you were right Subwo1, I have an excuse to get intimate with LTspice now........but.....I am not afraid.
I only hope I dont' get that far just to find out It cant' use other models or doesn't have many other than LT models!
I've heard nothing but good things about it though, from all over, never anything bad!!!
This might be a good thing actually, if we have Ltspice (a good, free simulator), and a circuit that's fully compatible with it, anyone and everyone can attempt it, and at no cost for software, or any limitations of trial versions!
Chris
subwo1 said:
Well, I became profficient with orcad in just a few days, largely due to their excellent tutorials, took me two days to go through them all lol...some twice.
I'm going through help files for ltspice now as a matter of fact, 3/4 way through it. Seems straightforward!! Interesting that it runs on linux with Wine....nice.
I like their appendix how they list all their included parts and what they actually are+ their featured characteristics.
Wish they all did that, should be manditory, not like pspice where I see all these symbols and then find out the dual output aspect is just part of the picture.
I'm sure there's alot more info out there on it as well, not just these help files.
So far I dont' think I'll switch over to it full time, but we've only just been introduced, though I like what I see. I couldn't believe it is only 4mb! It honestly took longer to install than it did to download.
I plan on having the same joke of a circuit I made up last night running on this very shortly but with a decent comparator this time, and with complimentary outputs.
I'll post it for kicks, Oh, and I will try it with Johans double integrator loop as well!
Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.