Because of base drive losses, BJTs can only compete in terms of efficiency in very high voltage low current applications where only a small current at ~0.7v is needed to switch a moderate power (high V, low I). In a class D amp driving 2 ohms a very large current will be required (again at ~0.7v) to switch a moderate power (high I, low V).
Yes, BJT are used in switching power supplies, but you'll note 99% of the time they are used on the primary side.
Have you ever seen a synchronous rectifier made with BJTs?
Yes, BJT are used in switching power supplies, but you'll note 99% of the time they are used on the primary side.
Have you ever seen a synchronous rectifier made with BJTs?
These are many complex issues being raised.
First, the Nyquist criterion is not an issue here. I only want a Subwoofer amp. So lets say it will never have to handle an audio signal of greater than 200hz.
So, then 400hz would be the minimum? Problem is that some will get through the filters, so it will be audible.
So the frequency question here is how low can I go and not have it be audible, subliminally noticable, or an environmental hazard for pets or wildlife?
Second, how big a magnetics would I have to use? Say I had a fourth order filter at 1000hz?
It would be comparable to a passive speaker crossover at 1000hz. There are people who make fancy foil wound inductors and all.
Also, if this is well designed, the filtering can be inside the feedback loop. So the signal being delivered to the driver is the one that will be compared with the input.
Early switching power supplies ran 20 to 25khz. This is still published as a frequency range for inverters where bipolars beat mos.
No, I have never seen a synchronous rectifier using BJT. But part of the reason they us MOS is to take advantage of the parasitic diodes. These diodes help in most of the duty cycle.
( I have seen on paper synchronous rectifiers using BJT )
Base drive current for BJT used in switching applications may not be trivial, but it is not a key issue.
The issue is thermal disipation in the output devices themselves. It it this thermal dissipation which makes such output devices heat up, and determines how much power you can get per device.
This thermal disipation in the output devices is caused by two factors. First, the on resistance or internal voltage drop. Second, the switching times, for both parts of the cycle.
So, at low freq, BJt is better. At high enough frequencies, MOS is better.
Now days, some people are saying that for certain speeds, and certain voltages and currents, GTOs are better, as are IGBT. There are also a few other new devices too.
But for this set up, its BJT or MOS. The transistion point is going to be somewhere around 25khz to 30khz.
What ever technology is used, there will be less heat in the output transistors if the switching frequency is lowered.
Ok.
But I don't want to talk about output technology yet. I started this thread to talk about frequency.
How low can I go, with out being a psychoacoustic problem??
Its likely to be around 27khz, 25khz, 22khz?
I would like to go much lower, to get better thermal efficiency in the output devices. But that would be audible.
There must be some conventional wisdom on this.
First, the Nyquist criterion is not an issue here. I only want a Subwoofer amp. So lets say it will never have to handle an audio signal of greater than 200hz.
So, then 400hz would be the minimum? Problem is that some will get through the filters, so it will be audible.
So the frequency question here is how low can I go and not have it be audible, subliminally noticable, or an environmental hazard for pets or wildlife?
Second, how big a magnetics would I have to use? Say I had a fourth order filter at 1000hz?
It would be comparable to a passive speaker crossover at 1000hz. There are people who make fancy foil wound inductors and all.
Also, if this is well designed, the filtering can be inside the feedback loop. So the signal being delivered to the driver is the one that will be compared with the input.
Early switching power supplies ran 20 to 25khz. This is still published as a frequency range for inverters where bipolars beat mos.
No, I have never seen a synchronous rectifier using BJT. But part of the reason they us MOS is to take advantage of the parasitic diodes. These diodes help in most of the duty cycle.
( I have seen on paper synchronous rectifiers using BJT )
Base drive current for BJT used in switching applications may not be trivial, but it is not a key issue.
The issue is thermal disipation in the output devices themselves. It it this thermal dissipation which makes such output devices heat up, and determines how much power you can get per device.
This thermal disipation in the output devices is caused by two factors. First, the on resistance or internal voltage drop. Second, the switching times, for both parts of the cycle.
So, at low freq, BJt is better. At high enough frequencies, MOS is better.
Now days, some people are saying that for certain speeds, and certain voltages and currents, GTOs are better, as are IGBT. There are also a few other new devices too.
But for this set up, its BJT or MOS. The transistion point is going to be somewhere around 25khz to 30khz.
What ever technology is used, there will be less heat in the output transistors if the switching frequency is lowered.
Ok.
But I don't want to talk about output technology yet. I started this thread to talk about frequency.
How low can I go, with out being a psychoacoustic problem??
Its likely to be around 27khz, 25khz, 22khz?
I would like to go much lower, to get better thermal efficiency in the output devices. But that would be audible.
There must be some conventional wisdom on this.
zenmasterbrian said:
Why wouldn't it be an issue here? Comparing the audio signal to a periodic signal is sampling, and yes 400Hz would be the min. Some will get through the filters and be audible which is exactly why people use much higher switching frequencies!!
zenmasterbrian said:
What's the highest frequnecy that can be detected by anything living? Take that and double it.
just to note, I'm already on the planning stage in building a class D sub amp doing 1kW into 1 ohm. I also want to lower the switching frequency but decided to use atleast 100kHz. more around 250kHz. 😀
I'm not trying to start anything here, but I'm curious......what's the point in asking in the first place if you don't want to accept the advice given to you?
I have about 300pcs of switching transistors and still haven't gone to using one of them because of the rather high current needed to keep them conducting compared to mosfets. why did I get them in the first place? coz I got them real cheap. $6 for the whole bag. I can use them someday when I build a SMPS that runs on a low voltage suppy that doesn't have enough voltage to keep a mosfet conducting effectively (<5V supplies)
I'm not trying to start anything here, but I'm curious......what's the point in asking in the first place if you don't want to accept the advice given to you?
I have about 300pcs of switching transistors and still haven't gone to using one of them because of the rather high current needed to keep them conducting compared to mosfets. why did I get them in the first place? coz I got them real cheap. $6 for the whole bag. I can use them someday when I build a SMPS that runs on a low voltage suppy that doesn't have enough voltage to keep a mosfet conducting effectively (<5V supplies)
zenmasterbrian said:
How does your jellybean pick bipolar compare to 5 or 10mOhm 100v mosfet in terms of saturation voltage? (100v rail is enough for 1kW to 4 ohms)
Fast-switching bipolar tranny with less than 0.25 Vce sat at 50 amps and square switching SOA?
SHOW THAT TO ME!
Conduction losses remain fairly constant with frequency, switching losses go up merely linearly with frequency.
You say that the frequency where BJTs overtake MOSFETs is around 30K, it follows that at 30k losses are equal for the two device types, it also follows that, given the relationships mentioned earlier, at frequencies near 30k the losses are nearly the same.
If you won't listen to us, pick whichever you prefer.
As for switching frequency, as long as it's above 20k people won't hear it, dogs, cats, bats, mice and the sort might hear it up to 100k. Go for 50k or so, then put a 1k low-pass on it.
With that, I leave this thread, having said all that is useful for me to have said.
You say that the frequency where BJTs overtake MOSFETs is around 30K, it follows that at 30k losses are equal for the two device types, it also follows that, given the relationships mentioned earlier, at frequencies near 30k the losses are nearly the same.
If you won't listen to us, pick whichever you prefer.
As for switching frequency, as long as it's above 20k people won't hear it, dogs, cats, bats, mice and the sort might hear it up to 100k. Go for 50k or so, then put a 1k low-pass on it.
With that, I leave this thread, having said all that is useful for me to have said.
The frequency is not the only issue. Even at slow frequency you still need fast ON and fast OFF to get real squarewave. Because here we talk about sound production that you don't want any distortion. While on switching power we can tolerate small distortion but the ear will hear even very small distortion.
So if you are sure the BJT can do good squarewave then it is fine. For frequency normally for full range, say 500kHz signal carrier the audio sampled at least 25Hz per cycle so for 400Hz = 400 x 25 = 10.000Hz. Or if you still worry about audible you can use 25kHz to 30khz. And make suitable filtering. A big filter maybe.
So please make a test for BJT performance and trial for frequency.
So if you are sure the BJT can do good squarewave then it is fine. For frequency normally for full range, say 500kHz signal carrier the audio sampled at least 25Hz per cycle so for 400Hz = 400 x 25 = 10.000Hz. Or if you still worry about audible you can use 25kHz to 30khz. And make suitable filtering. A big filter maybe.
So please make a test for BJT performance and trial for frequency.
That BJT out performs MOS for modest frequency switching is well documented.
I got a book coming in which goes into this.
If you have links for especially attractive MOS, lets see em.
You might be talking about stuff much bigger than TO-3.
Well, there are BJt bigger than TO-3 too.
As far as distortion, remember that the filtering is inside the feedback loop.
As far as sampling being adequate, 20khz is plenty for a 200hz audio signal.
As far as filtering at 1000hz, fine. But some of the switching signal is going to get through.
There must be some psychoacoustic data about what people and animals would percieve. I don't plan on doubling anything. Instead, I plan on using well what information is available.
An amp for 200hz is not the same as a broad band audio amp.
It is also not the same as a switching power supply.
This minimum switching frequency requirement is external. It has to do with humans and animals. I'm willing to listen to anyone who actually knows anything about that.
I got a book coming in which goes into this.
If you have links for especially attractive MOS, lets see em.
You might be talking about stuff much bigger than TO-3.
Well, there are BJt bigger than TO-3 too.
As far as distortion, remember that the filtering is inside the feedback loop.
As far as sampling being adequate, 20khz is plenty for a 200hz audio signal.
As far as filtering at 1000hz, fine. But some of the switching signal is going to get through.
There must be some psychoacoustic data about what people and animals would percieve. I don't plan on doubling anything. Instead, I plan on using well what information is available.
An amp for 200hz is not the same as a broad band audio amp.
It is also not the same as a switching power supply.
This minimum switching frequency requirement is external. It has to do with humans and animals. I'm willing to listen to anyone who actually knows anything about that.
Why you are worry about effect switching frequency for human and animal?
There is no accoustic sound production since you use filter. Very easy to remove high frequency isn't? And remember that you use woofer instead of tweeter. Both you amp and speaker did not produce high audible ultrasonic.
It is not make sense that so far you worry about creature injured by your amp for me.
There is no accoustic sound production since you use filter. Very easy to remove high frequency isn't? And remember that you use woofer instead of tweeter. Both you amp and speaker did not produce high audible ultrasonic.
It is not make sense that so far you worry about creature injured by your amp for me.
OK this is googling from me free of charge for you:
http://www.lsu.edu/deafness/HearingRange.html
Species Approximate Range (Hz):
human 64-23,000
dog 67-45,000
cat 45-64,000
cow 23-35,000
horse 55-33,500
sheep 100-30,000
rabbit 360-42,000
rat 200-76,000
mouse 1,000-91,000
gerbil 100-60,000
guinea pig 54-50,000
hedgehog 250-45,000
raccoon 100-40,000
ferret 16-44,000
opossum 500-64,000
chinchilla 90-22,800
bat 2,000-110,000
beluga whale 1,000-123,000
elephant 16-12,000
porpoise 75-150,000
goldfish 20-3,000
catfish 50-4,000
tuna 50-1,100
bullfrog 100-3,000
tree frog 50-4,000
canary 250-8,000
parakeet 200-8,500
cockatiel 250-8,000
owl 200-12,000
chicken 125-2,000
http://www.lsu.edu/deafness/HearingRange.html
Species Approximate Range (Hz):
human 64-23,000
dog 67-45,000
cat 45-64,000
cow 23-35,000
horse 55-33,500
sheep 100-30,000
rabbit 360-42,000
rat 200-76,000
mouse 1,000-91,000
gerbil 100-60,000
guinea pig 54-50,000
hedgehog 250-45,000
raccoon 100-40,000
ferret 16-44,000
opossum 500-64,000
chinchilla 90-22,800
bat 2,000-110,000
beluga whale 1,000-123,000
elephant 16-12,000
porpoise 75-150,000
goldfish 20-3,000
catfish 50-4,000
tuna 50-1,100
bullfrog 100-3,000
tree frog 50-4,000
canary 250-8,000
parakeet 200-8,500
cockatiel 250-8,000
owl 200-12,000
chicken 125-2,000
zenmasterbrian said:
Are you even reading anything being posted in this thread? I am utterly amazed how you continue to bypass all reaonable thought and end up going back to your original question which has been answered numerous times and is not dificult to answer in the first place.
Why don't you build this bipolar based behemoth and tweak the switching frequency yourself to see what what works and what doesn't?
kartino, than you for finding that reference. I'm still reviewing the article.
It does seem that the hearing limit is fuzzy.
I've decided on a tentative frequency specification.
23.5khz.
Now, the amp only has to go to 300hz absolute maximum. Typically much lower.
So there will be a filter. I've decided on 8th order.
Remember, increasing the order of such filters does not increase the total reactance. Rather, it just distributes it.
It will be comparable to a LP speaker crossover at 1000hz.
The total amount of potential 23.5khz power will be about 2x the amps sine wave output power.
But by 16khz it will be down 144dB.
By 22.6khz it will be an extra 5th up, so it will be down 156dB.
Now, I spent some time reading audio books last night, and reflecting on common experience.
1. 20khz audio propagates very poorly through air. It attenuates very very quickly. It is very directional. It won't do well at all with a subwoofer for a driver. It really can't even get through most grill cloths. Common cloth is very opaque to it. It is highly directional.
So, I am not going to worry about outdoor animals and this system.
2. With all due respect to kartino's article, 20khz is a real stretch for human hearing. Even when it is there, the sensitivity is low.
Before reading it I had picked 23.5khz, which I will explain more about.
3. I will plan on extra acoustic filtering in the form of a foam rubber grill cloth that is on a close fitting frame.
4. The filter, and much of the other circuitry will be well enclosed. Say wire fly screen, and then plexiglass on top of that. I still want to show this off.
I will continue to look at any additional information about human and animal sensitivity to ultrasonics, as well as what precedents there are for appliances that might generate them.
Again, back in the 70's, switching power supplies typically ran in the 20khz to 25khz range.
Also, before I build this, I will experiment with a woofer and a signal generator, running the frequency way up.
I will also experiment with the smallest of dome tweaters and piezo tweaters, going to 23.5. I will let other people and animals experience it.
More about 23.5 khz in next post
It does seem that the hearing limit is fuzzy.
I've decided on a tentative frequency specification.
23.5khz.
Now, the amp only has to go to 300hz absolute maximum. Typically much lower.
So there will be a filter. I've decided on 8th order.
Remember, increasing the order of such filters does not increase the total reactance. Rather, it just distributes it.
It will be comparable to a LP speaker crossover at 1000hz.
The total amount of potential 23.5khz power will be about 2x the amps sine wave output power.
But by 16khz it will be down 144dB.
By 22.6khz it will be an extra 5th up, so it will be down 156dB.
Now, I spent some time reading audio books last night, and reflecting on common experience.
1. 20khz audio propagates very poorly through air. It attenuates very very quickly. It is very directional. It won't do well at all with a subwoofer for a driver. It really can't even get through most grill cloths. Common cloth is very opaque to it. It is highly directional.
So, I am not going to worry about outdoor animals and this system.
2. With all due respect to kartino's article, 20khz is a real stretch for human hearing. Even when it is there, the sensitivity is low.
Before reading it I had picked 23.5khz, which I will explain more about.
3. I will plan on extra acoustic filtering in the form of a foam rubber grill cloth that is on a close fitting frame.
4. The filter, and much of the other circuitry will be well enclosed. Say wire fly screen, and then plexiglass on top of that. I still want to show this off.
I will continue to look at any additional information about human and animal sensitivity to ultrasonics, as well as what precedents there are for appliances that might generate them.
Again, back in the 70's, switching power supplies typically ran in the 20khz to 25khz range.
Also, before I build this, I will experiment with a woofer and a signal generator, running the frequency way up.
I will also experiment with the smallest of dome tweaters and piezo tweaters, going to 23.5. I will let other people and animals experience it.
More about 23.5 khz in next post
23.5khz i say. but actually i want a range of 23.5 to 25.5.
I want this to have an unusual and not strictly necessary feature of being able to synchronize, phase lock.
Consider this an audiophiles purism.
If there are any drawbacks to this time domain sampling, it can be minimized by such.
So this amp could phase lock to another amp of the same design, or to a digital source.
So, it is 23.5Khz absolute minimum, and when running free.
If there are multiple amps in the system, you is switched into leader mode, at 24khz.
If there is a DVD, it locks at the 24khz.
If it is CD audio, then the 44.1 x 4/7 = 25.2khz.
I know this is unnecessay, and not provided for in most consumer gear. I know it means extra wires and all. But I still want this capability.
But this PLL is done so that never ever does it go below 23.5.
Also there is a sentinel circuit that watches both the speaker terminals, and the input to the filter. If this thing slows for one cycle, the speaker relay opens, and the power mains locking relay is released.
I want this to have an unusual and not strictly necessary feature of being able to synchronize, phase lock.
Consider this an audiophiles purism.
If there are any drawbacks to this time domain sampling, it can be minimized by such.
So this amp could phase lock to another amp of the same design, or to a digital source.
So, it is 23.5Khz absolute minimum, and when running free.
If there are multiple amps in the system, you is switched into leader mode, at 24khz.
If there is a DVD, it locks at the 24khz.
If it is CD audio, then the 44.1 x 4/7 = 25.2khz.
I know this is unnecessay, and not provided for in most consumer gear. I know it means extra wires and all. But I still want this capability.
But this PLL is done so that never ever does it go below 23.5.
Also there is a sentinel circuit that watches both the speaker terminals, and the input to the filter. If this thing slows for one cycle, the speaker relay opens, and the power mains locking relay is released.
Audiophile stuff is extreme and personal. It is designed to be the best possible.
It is designed for exactly what it does, not in imitation of other appiances.
This is for a multi-amped system. This is not a broad band amp. This is not a compact, low cost, switching power supply for a computer, either.
A pair of linear tweeter amps using mosfets, to go with this, is likely.
It is designed for exactly what it does, not in imitation of other appiances.
This is for a multi-amped system. This is not a broad band amp. This is not a compact, low cost, switching power supply for a computer, either.
A pair of linear tweeter amps using mosfets, to go with this, is likely.
Now, if anyone has any additional information about human or animal sensitivity to ultrasonics, I would be very interested in seeing it.
Also, if anyone does want to post links to low resistance transitor data sheets, I would like to look at it. BJT, or MOS, or anything else.
If anyone has info about such circuit designs and their issues, I would like to see it.
If there are books especially good about class D, or even about switching power supplies, I would like to know.
Also, if anyone does want to post links to low resistance transitor data sheets, I would like to look at it. BJT, or MOS, or anything else.
If anyone has info about such circuit designs and their issues, I would like to see it.
If there are books especially good about class D, or even about switching power supplies, I would like to know.
This amp is not going to be small.
The subwoofer enclosure it is integrated into will not be small either.
The subwoofer enclosure it is integrated into will not be small either.
Good luck with that!zenmasterbrian said:
All very good points.zenmasterbrian said:
My upper limit is around 17kHz. Amazingly enough my father's upper limit is 21kHz. He's 59. I know he's not lying either because he could tell me when I switched my tone generator on and off while not looking at me! Everybody's hearing is slightly different.zenmasterbrian said:
I'm planning on two versions of this amp, small and big.
The small one is for a movable subwoofer. So it plugs into 115VAC, and at power peaks will take about the most you can get out of a 15A outlet.
This is about 180O Watts. So it will have an 1800 Watt toroidal power transformer. The steady state power is much much less. But the core has to be big enough for that 1800W.
The large version is for a built-in subwoofer. This will have an even bigger transformer, which is hard wired to 230VAC. Its power will be far greater. As long as I leave the electric stove off, I've got 12,000 Watts of service to play with, although its for all the audio channels.
( At the San Jose Tech museum there is an earth quake simulator which has a 12KW or 20KW sound system! )
Part of the reason for wanting such extreme capabilites, is just purism. But I am also interested in the 64' pipe organ octave. I want to experiment with infrasonics. Specifically going down to 8hz, or maybe a bit lower. I'm not sure if this can really be used in music, but I want to experiment. There are three pipe organs in the world which will do the 8hz.
I believe it could make for a very interesting kind of ambient music.
This system will also make for superb bass for the more standard musical range.
The 32' organ octave, going down to 16hz, sounds wonderful!
A 32" kettle drum ( the most common large ones are 28", for 16' F ) will go down to 16' C, at 32hz.
I once heard a cover of Niel Young's "Old Man Take a Look at Your Life" The song was in the key of D, and they used a pair of such kettle drums at C# and D. It sounded wonderful.
I know that some stuff is on the market now that does not use power transformers. I have reservations about this.
All of these matter I have broached in subwoofers->Giant Subwoofer.
The small one is for a movable subwoofer. So it plugs into 115VAC, and at power peaks will take about the most you can get out of a 15A outlet.
This is about 180O Watts. So it will have an 1800 Watt toroidal power transformer. The steady state power is much much less. But the core has to be big enough for that 1800W.
The large version is for a built-in subwoofer. This will have an even bigger transformer, which is hard wired to 230VAC. Its power will be far greater. As long as I leave the electric stove off, I've got 12,000 Watts of service to play with, although its for all the audio channels.
( At the San Jose Tech museum there is an earth quake simulator which has a 12KW or 20KW sound system! )
Part of the reason for wanting such extreme capabilites, is just purism. But I am also interested in the 64' pipe organ octave. I want to experiment with infrasonics. Specifically going down to 8hz, or maybe a bit lower. I'm not sure if this can really be used in music, but I want to experiment. There are three pipe organs in the world which will do the 8hz.
I believe it could make for a very interesting kind of ambient music.
This system will also make for superb bass for the more standard musical range.
The 32' organ octave, going down to 16hz, sounds wonderful!
A 32" kettle drum ( the most common large ones are 28", for 16' F ) will go down to 16' C, at 32hz.
I once heard a cover of Niel Young's "Old Man Take a Look at Your Life" The song was in the key of D, and they used a pair of such kettle drums at C# and D. It sounded wonderful.
I know that some stuff is on the market now that does not use power transformers. I have reservations about this.
All of these matter I have broached in subwoofers->Giant Subwoofer.
BWRX, how much signal strength do you need to have for your father to hear 21khz.
And what are you using for a transducer?
What do you believe is the lowest ultrasonic people can be exposed to on a continual basis, without being even subliminally effected?
And what are you using for a transducer?
What do you believe is the lowest ultrasonic people can be exposed to on a continual basis, without being even subliminally effected?
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