zenmasterbrian said:
How do you manage personal relationships whilst being such a vacantly pretentious person?
DNA
Like 1-2kV and several kA capable bipolars? 😀Workhorse said:
OK, fair enough, your mosfet has a little bit better switching charasteristics 😀
MOS still has higher on resistances than Bipolar, agreed?
At a low switching freq, bipolar can still do more power with the same number of transistors and the same heat sink.
The issue is, what frequency is the turning point.
But before that, what frequency needs to be used here?
That's why I started this thread this way.
At a low switching freq, bipolar can still do more power with the same number of transistors and the same heat sink.
The issue is, what frequency is the turning point.
But before that, what frequency needs to be used here?
That's why I started this thread this way.
Paralleling mosfets is better than paralleling bipolar devices because mosfets have a positive temperature coeffiecient and bipolars have a negative temperature coefficient.
Since mosfets perform better at higher switching frequencies than bipolars there's no reason they wouldn't be superior at lower switching frequencies as well.
Bipolars are current gain devices so whatever advantage they may have in on state resistance will be lost in the required base drive circuitry.
Just shoot for a switching frequency around 100kHz as a starting point.
Since mosfets perform better at higher switching frequencies than bipolars there's no reason they wouldn't be superior at lower switching frequencies as well.
Bipolars are current gain devices so whatever advantage they may have in on state resistance will be lost in the required base drive circuitry.
Just shoot for a switching frequency around 100kHz as a starting point.
Hi classd4sure
APT for now is the only device that can handle the power output I need with only 4 output. I have made lot of test, even with IXYS and for now only APT is able to handle that power at that effiency...Something special here!
Fredos
www.d-amp.com
APT for now is the only device that can handle the power output I need with only 4 output. I have made lot of test, even with IXYS and for now only APT is able to handle that power at that effiency...Something special here!
Fredos
www.d-amp.com
Switching power supplies went to 40khz and 100khz, and beyond because they want the magnetics to be as small as possible.
So their design requires MOSFETs.
But for this, a Class D subwoofer amp, minimizing the size of the magnetics is not an issue.
Rather, I'd like to get the highest efficiency possible.
How high, depends on how low the switching frequency can be.
Assume the amp never has to deal with anything greater than 200hz.
So, for the Nyquist criterion, I just need 400hz, plus some filtering buffer.
But in practice, it is had to filter at that low of frequencies. Also, there will still be some of the switching signal left.
So I believe it has to be ultrasonic.
Are there examples where people built class D and kept in in say the 22khz range to 30khz????
I don't want to irritate dogs. Is there some agreed upon minimum frequency for such things???
So their design requires MOSFETs.
But for this, a Class D subwoofer amp, minimizing the size of the magnetics is not an issue.
Rather, I'd like to get the highest efficiency possible.
How high, depends on how low the switching frequency can be.
Assume the amp never has to deal with anything greater than 200hz.
So, for the Nyquist criterion, I just need 400hz, plus some filtering buffer.
But in practice, it is had to filter at that low of frequencies. Also, there will still be some of the switching signal left.
So I believe it has to be ultrasonic.
Are there examples where people built class D and kept in in say the 22khz range to 30khz????
I don't want to irritate dogs. Is there some agreed upon minimum frequency for such things???
Just use 100KHz like suggested and get on with it, 3 pages about this now and still no decision. Or design your circuit so you can adjust the frequency easily between say 50KHz and 100KHz and get going on some real design.
-SL
-SL
OK Zen Master, we are waiting your 'big base driver' maybe we can use your design to drive mosfet too.
Anyway as I know so far, the winner for smallest 'on resistance' is still APT18_, do you have candidate from bipolar?
Anyway as I know so far, the winner for smallest 'on resistance' is still APT18_, do you have candidate from bipolar?
I'd have to look in data books. But with a pair of TO-3 bipolars on large heat sinks, no fans, you can do 200 watts for recorded music. For PA or musical instrument that number will be lower.
MOS will generate more heat for the same current flow. So you will need more of them.
Wheter MOS works better or bipolar does, is largely a matter of frequency. MOS will be better above a certain frequency.
So the place to start here is frequency.
So, is there some standard for low high you have to be, so as not to bother dogs or cats, etc, with ultrasonic getting through a filter?😎
MOS will generate more heat for the same current flow. So you will need more of them.
Wheter MOS works better or bipolar does, is largely a matter of frequency. MOS will be better above a certain frequency.
So the place to start here is frequency.
So, is there some standard for low high you have to be, so as not to bother dogs or cats, etc, with ultrasonic getting through a filter?😎
Frankly I don't think you have the knowledge to undertake such a project.
You seem to be confusing class B amps with class D.
The same current with the same voltage across the device will produce the same power dissapation no matter what type of transistor it is. P = V * I, device type doesn't enter into the equation.
When I said 200 watts for a pair of T0-3 bipolars, I meant class B.
I say this, because it is more than you could do with a pair of MOS transistors.
MOS drops more voltage, so it generates more heat.
At low enough frequencies, bipolar will get better efficiency in class D, than does MOS.
Early switching power supplies were always bipolar. They went to higher frequencies to get the size of the magnetics down, ans so they have to use MOS.
So the question is, how low can the switching frequency be for a Class D subwoofer amp?
Is there a good book that addresses this?😎
I say this, because it is more than you could do with a pair of MOS transistors.
MOS drops more voltage, so it generates more heat.
At low enough frequencies, bipolar will get better efficiency in class D, than does MOS.
Early switching power supplies were always bipolar. They went to higher frequencies to get the size of the magnetics down, ans so they have to use MOS.
So the question is, how low can the switching frequency be for a Class D subwoofer amp?
Is there a good book that addresses this?😎
zenmasterbrian said:
Say you're using an IRFZ48 like RX5 did in his project. That will have an on state resistance of 18mohms with a Vgs of 10V and a drain current of 43A. That equates to a voltage drop across the fet of only 0.774V. And that's only a continuous rating. When switching it can obviously handle more peak current and the losses will be lower. Don't forget that you'll only need to charge the gate up once and hold it there to keep the fet conducting. Don't forget you'll need to supply continuous current to the base to keep the bjt conducting. With the lower gain of power bjts you may need an amp or more of base current to saturate a bjt with a 43A collector current. Now, what sort of power dissipation will a similar bipolar device have?
Read through this if you haven't already:
http://sound.westhost.com/articles/pwm.htm
There IS a reason you don't see many class d amps using bipolar devices anymore.
I'll read you materials, and any more you can supply.
If you can supply a link for that transistor? Especially a book all about class D design.
But I know you can do more power per transistor at low frequency with Bipolar. It is a vertical process, so the resistance is lower.
A 40khz MOS switching power supply has better efficiency than a 100khz MOS switching power supply.
A 25khz MOS switching power supply will have still better efficiency. And at that low a frequency, a Bipolar switching power supply will have even better efficiency.
The move to higher frequency was to get smaller magnetics in switching power supplies, and to get good broad band audio.
I don't care about smallest magnetics. And I just want a subwoofer amp.
The question I am really posing is how low a frequency can I go? Some will get through the filtering. So it seems that it must be ultrasonic.
But how high? It seems an environmental concern?
Is 25khz high enough? Will that not be perceptible, even subliminally? And will it bother animals?
( if it bothers insects, I'll be pleased )
Lets address the frequency issue, then the implementation technology.
If you can supply a link for that transistor? Especially a book all about class D design.
But I know you can do more power per transistor at low frequency with Bipolar. It is a vertical process, so the resistance is lower.
A 40khz MOS switching power supply has better efficiency than a 100khz MOS switching power supply.
A 25khz MOS switching power supply will have still better efficiency. And at that low a frequency, a Bipolar switching power supply will have even better efficiency.
The move to higher frequency was to get smaller magnetics in switching power supplies, and to get good broad band audio.
I don't care about smallest magnetics. And I just want a subwoofer amp.
The question I am really posing is how low a frequency can I go? Some will get through the filtering. So it seems that it must be ultrasonic.
But how high? It seems an environmental concern?
Is 25khz high enough? Will that not be perceptible, even subliminally? And will it bother animals?
( if it bothers insects, I'll be pleased )
Lets address the frequency issue, then the implementation technology.
BWRX, what power spec is on the data sheet for the transistor you mention?
Understand that that power spec is just a measure of its thermal resistance. It is die size, the package, and the mounting substrate thickness, between the die and the package. It is also substrate material.
For bipolars, in the Motorola catalog, the highest is 350W, NPN only. Then there is a pair of complementaries at 300W.
But the breakdown voltage is really too low for audio.
Then there are transistors at 250W, complementary. These are widely used for audio.
Actually the TO-3 power rating is the same as for PowerTab. But! That will drop more for power tab if you have it insulated from the heatsink.
These numbers are for the case being kept at 25 deg C, which is unrealistic.
What is it for your best MOS?
But also understand that with a switching, or Class D application, the power disipated in the output transistors is due to switching speed and on resistance.
For on resistance, bipolar will be better.
But lets first focus on frequency, how low can this be? Then look at technology.
Understand that that power spec is just a measure of its thermal resistance. It is die size, the package, and the mounting substrate thickness, between the die and the package. It is also substrate material.
For bipolars, in the Motorola catalog, the highest is 350W, NPN only. Then there is a pair of complementaries at 300W.
But the breakdown voltage is really too low for audio.
Then there are transistors at 250W, complementary. These are widely used for audio.
Actually the TO-3 power rating is the same as for PowerTab. But! That will drop more for power tab if you have it insulated from the heatsink.
These numbers are for the case being kept at 25 deg C, which is unrealistic.
What is it for your best MOS?
But also understand that with a switching, or Class D application, the power disipated in the output transistors is due to switching speed and on resistance.
For on resistance, bipolar will be better.
But lets first focus on frequency, how low can this be? Then look at technology.
Actually, for Class D audio, that 350W Motorola transistor could be the way to go.
Given that I'll probably be at 4 or 2 ohms, so I won't need a huge voltage, and given that Class D would not seem to benefit from any push pull or four transistor bridge, that 350w NPN could be the way. Some could be paralleled ( with small emitter resistors ) and run between a positive and negative supply, with the filter components.
Maybe not. maybe still need two transistors.
But anyway, I know class D will be much different from linear.
First, is there any agreement on how low a frequency you can spew out in a driver, without being considered an environmental hazard????
Given that I'll probably be at 4 or 2 ohms, so I won't need a huge voltage, and given that Class D would not seem to benefit from any push pull or four transistor bridge, that 350w NPN could be the way. Some could be paralleled ( with small emitter resistors ) and run between a positive and negative supply, with the filter components.
Maybe not. maybe still need two transistors.
But anyway, I know class D will be much different from linear.
First, is there any agreement on how low a frequency you can spew out in a driver, without being considered an environmental hazard????
I would love to see a book that analyzes all the aspects of class D audio.
I suspect that two NPNs in the quaisi complementary config. is the best way. So, an emitter follower on top of a common emitter.
But again, frequency?
Say I have a 1000Watt amp. Say I've got a filter that takes the switching signal down 50dB!!
Say this amp puts 0.1 watts on the driver at the switching freq any time it is turned on.
Now, the driver is a stout subwoofer. It won't be bothered by this. Also, overall efficiency is not bothered by this.
But is it a psycho acoustic problem?? Would it bother humans? How about birds and animals?
If it was 0.1 watts at 25khz? Is that ok?
22khz ?? It makes a difference. From tables I've seen, there are efficiency drops when you start to go higher. Also, you need to go to MOS. This does not increase the efficiency, but it does stop it from being degraded as much.
So the first question is how low can the switching frequency be?😎
I suspect that two NPNs in the quaisi complementary config. is the best way. So, an emitter follower on top of a common emitter.
But again, frequency?
Say I have a 1000Watt amp. Say I've got a filter that takes the switching signal down 50dB!!
Say this amp puts 0.1 watts on the driver at the switching freq any time it is turned on.
Now, the driver is a stout subwoofer. It won't be bothered by this. Also, overall efficiency is not bothered by this.
But is it a psycho acoustic problem?? Would it bother humans? How about birds and animals?
If it was 0.1 watts at 25khz? Is that ok?
22khz ?? It makes a difference. From tables I've seen, there are efficiency drops when you start to go higher. Also, you need to go to MOS. This does not increase the efficiency, but it does stop it from being degraded as much.
So the first question is how low can the switching frequency be?😎
Hi ZEN,
What made you to think THAT MOSFETS PRODUCE MORE HEAT DISSIPATION THAN BIPOLARS....
regards,
K a n w a r
What made you to think THAT MOSFETS PRODUCE MORE HEAT DISSIPATION THAN BIPOLARS....
regards,
K a n w a r
In a linear amp situation the disipation is not going to be higher. But still, the MOS devices are not usually able to disipate as much.
Here, I am looking at Power Control with Solid-State Devices by Irving M. Gottlieb.
He says that ON resistance of MOS is clearly higher than comparable size bipolars. So when used in a switching power supply or class D amp, the thermal disipation will be higher for MOS.
Right now, I want to talk about frequency.
According to Gottlieb, early switching power supplies ran at 20khz to 25khz, and were bipolar.
They didn't want to run slower because of audible noise.
The move to higher frequencyies was facilitated by MOS, but the purpose was smaller magnetics. MOS lets you get the higher frequency and smaller magnetics, but it still does have a higher on resistance.
Clearly for a broadband, up to 20khz class D audio amp, you need to use more than 40Khz, and most probably will go MOS.
But I am only interested in a subwoofer amp.
So how low can I go, given that some of the switching frequency will get through the filter? 25khz? 24khz? 22khz?
I don't want to create anykind of negative psychosubliminal effect. There must be some conventional wisdom on this.
After this is resolved, we can look at semiconductor technology.
Here, I am looking at Power Control with Solid-State Devices by Irving M. Gottlieb.
He says that ON resistance of MOS is clearly higher than comparable size bipolars. So when used in a switching power supply or class D amp, the thermal disipation will be higher for MOS.
Right now, I want to talk about frequency.
According to Gottlieb, early switching power supplies ran at 20khz to 25khz, and were bipolar.
They didn't want to run slower because of audible noise.
The move to higher frequencyies was facilitated by MOS, but the purpose was smaller magnetics. MOS lets you get the higher frequency and smaller magnetics, but it still does have a higher on resistance.
Clearly for a broadband, up to 20khz class D audio amp, you need to use more than 40Khz, and most probably will go MOS.
But I am only interested in a subwoofer amp.
So how low can I go, given that some of the switching frequency will get through the filter? 25khz? 24khz? 22khz?
I don't want to create anykind of negative psychosubliminal effect. There must be some conventional wisdom on this.
After this is resolved, we can look at semiconductor technology.
zenmasterbrian said:
It's called the nyquist criterion. The absolute minimum sampling frequency required is 2x the maximum frequency being sampled.
zenmasterbrian said:
You make it sound like you want to use humongous inductors and capacitors??? Smaller magnetics are beneficial for a number of reasons. You can get higher quality components that are smaller and have less parasitics. They can obviously cost less too.
Higher switching frequencies push the noise further away from the audio band and allow the use of lower value inductors and caps which again have reduced parasitics.
If you're having trouble deciding on a switching frequency and think bipolars are better than mosfets how are you going to design a 1000W amp? Not bashing you or anything, more curious than anything.
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