Hi,
I want to know what is the selection of high power mosfet (N channel) for audio amplifier purpose. Currently I use 2sk 3911 (Toshiba), seems it has high spec (600V, 20A), but very high input capacitance (around 4nF).
Considering another kind of MOSFET to get more clear, nice sound of my DIY power amp, or just to parallel the same mosfet to get more damping factor?
Some mosfet available e.g. IRFP 240 (popular), 2sk 1058 (also popular) etc. The original design is using IRFP 350 hexfet. There are some other mosfets available in my local market (not remember).
Thanks,
Ervin L
I want to know what is the selection of high power mosfet (N channel) for audio amplifier purpose. Currently I use 2sk 3911 (Toshiba), seems it has high spec (600V, 20A), but very high input capacitance (around 4nF).
Considering another kind of MOSFET to get more clear, nice sound of my DIY power amp, or just to parallel the same mosfet to get more damping factor?
Some mosfet available e.g. IRFP 240 (popular), 2sk 1058 (also popular) etc. The original design is using IRFP 350 hexfet. There are some other mosfets available in my local market (not remember).
Thanks,
Ervin L
Any schematic available?
2SK1058 is a lateral mosfet. It does not require temperature compensation as do the vertical types like IRFPXXX ect in Class AB bias. Look at the transfer characteristics of these two devices and you will notice the zero temperature coefficients is not the same. The vertical types require some type of temp compensation, as do BJT's, at class AB bias levels even if it is Quasi.
Damping factor has much more to do with the drive circuit than it does the overall Gm. Paralleling many together won't help you much with this variable.
2SK1058 is a lateral mosfet. It does not require temperature compensation as do the vertical types like IRFPXXX ect in Class AB bias. Look at the transfer characteristics of these two devices and you will notice the zero temperature coefficients is not the same. The vertical types require some type of temp compensation, as do BJT's, at class AB bias levels even if it is Quasi.
Damping factor has much more to do with the drive circuit than it does the overall Gm. Paralleling many together won't help you much with this variable.
Which one is better for MOSFET Power Audio Amplifier, higher voltage or higher current (e.g. to achieve linearity, slew rate, good damping factor, low THD etc)?
I ask this basically to enhance current DIY Power Follower (Pavel Macura based).
If there should be thermal adjustment/compensation, how to do so with this simple SE Class A? I also notice when it runs hot, the bias setting will be different than when it is cold (different voltage measured at source).
Or does it mean using lateral MOSFET is better for this schematic (instead the original was IRFP 350, an HEXFET, and some other schema is IRFP 240 and 150).
I ask this basically to enhance current DIY Power Follower (Pavel Macura based).
If there should be thermal adjustment/compensation, how to do so with this simple SE Class A? I also notice when it runs hot, the bias setting will be different than when it is cold (different voltage measured at source).
Or does it mean using lateral MOSFET is better for this schematic (instead the original was IRFP 350, an HEXFET, and some other schema is IRFP 240 and 150).
The lateral mosfets have their thermal advantages, but also lower transconductance. I think that they sound great, but so do the IRF and Fairchild MOSFETs I use in my F5 amps.
Troy Huebner wrote application note for National Semi in which he discussed the merits -- I think that the best measured results came from the 2SJ201/2SK1530 -- but these do need some thermal compensation. The Ap Note is, I believe, AN-1645. In his case, the driver they were using (a Nat Semi chip) couldn't provide sufficient bias to the IRF devices, and he notes that this is a shortcoming of the analysis.
Troy Huebner wrote application note for National Semi in which he discussed the merits -- I think that the best measured results came from the 2SJ201/2SK1530 -- but these do need some thermal compensation. The Ap Note is, I believe, AN-1645. In his case, the driver they were using (a Nat Semi chip) couldn't provide sufficient bias to the IRF devices, and he notes that this is a shortcoming of the analysis.
I have had good results with IRFP240. Its input capacitance is quite low compared to other IRFP series. They are also very cheap compared to some of the more exotic MOSFET's.
Vertical power MOSFETs (and similar technologies, such as PI and trench types like Toshiba J200/K1530) tend to have a 'sweet spot' where the capacitance, gm and current are sensible enough tp get good performance in audio - usually this happens in MOSFETs with Vdsmax between 100 and 300V - usually on the lower end of this range for P channel MOSFETs, and on the higher end for N channel MOSFETs fro, the IRF(P) and similar MOSFETs. For the same geometry, P and N channel MOSFETs get to have different characteristics so it's not trivial to find complementary pairs, unless the MOSFETs were not made to be pairs, like the Toshiba parts - if you opened up the case, you would find completely different chips inside, size wise as well as what is diffused on the silicon.
What i am trying to say is, there are a LOT of MOSFETs that will produce great results in amps IF you know how to use them properly - just like any ather part. But there are hidden pitfalls - like finding correct complementaries in the case of IRF(P) types, for instance. Also, the output stages can topologically be quite different in order to drive MOSFETs correctly - it's not just a case of sticking different output devices into the amp and biassing them properly. One thing to look out for and handle, is the nonlinearity of input capacitance, as well as gm at low drain currents. All MOSFETs have this problem, however, progress in the way MOSFETs are normally used (power electronics) tend to provide ever better characteristics for N channel MOSFETs which points to use in single ended class A or quasicomp circuits of multiple kinds. That, just like declaring a single type of MOSFET is 'best' just means you happen to be satisfied with solving the problems inherent in ANY MOSFET by the brute force method at hand, and declare the trade-off (and there is always one or more of those) as acceptable - when in fact, it's all the same underlying physics and set of problems, just in different amounts, producing different 'flavors' of the same basic behavior.
What i am trying to say is, there are a LOT of MOSFETs that will produce great results in amps IF you know how to use them properly - just like any ather part. But there are hidden pitfalls - like finding correct complementaries in the case of IRF(P) types, for instance. Also, the output stages can topologically be quite different in order to drive MOSFETs correctly - it's not just a case of sticking different output devices into the amp and biassing them properly. One thing to look out for and handle, is the nonlinearity of input capacitance, as well as gm at low drain currents. All MOSFETs have this problem, however, progress in the way MOSFETs are normally used (power electronics) tend to provide ever better characteristics for N channel MOSFETs which points to use in single ended class A or quasicomp circuits of multiple kinds. That, just like declaring a single type of MOSFET is 'best' just means you happen to be satisfied with solving the problems inherent in ANY MOSFET by the brute force method at hand, and declare the trade-off (and there is always one or more of those) as acceptable - when in fact, it's all the same underlying physics and set of problems, just in different amounts, producing different 'flavors' of the same basic behavior.
The IRFP240/9240 pair are by far not compliemntary yet you can still design a decent amplifier using them.
A lof of differences are reduced by using lots of feedback.
True, but as you know, the best way not to have a problem is not to correct it when it's there, but not to have it in the first place. This sort of thing tends to result in abuse of NPV. One other possibility would be to put a source resistor on the IRFP240, but not on the 9240. Or, simply, use IRFP340 instead of IRFP240. My point is, know thy MOSFETs 
- there are many methods to make them sing.
- there are many methods to make them sing.
Hi Ervin,
We have designed some unique lateral MOSFETs which are much better than most others out there. I would highly recommend you try them out.
Currently we have a 125W N / P Channel and a 250W N / P Channel.
The specifications are on the website (Pro Audio - Alfet Lateral MOSFETs) which should tell you all the information you need to know. They can be purchased from Lateral MOSFETs - Class-d Limited should you take an interest to them.
If you have any questions at all we will be more than happy to help you. The best thing to do is speak to our technical director (Mike) on 07980 600 373 and he will be able to tell you everything you need to know. Alternatively, you can drop him an email mike@proaudio.ltd.uk and he will get back to you shortly.
Best of luck,
Pro Audio Ltd
We have designed some unique lateral MOSFETs which are much better than most others out there. I would highly recommend you try them out.
Currently we have a 125W N / P Channel and a 250W N / P Channel.
The specifications are on the website (Pro Audio - Alfet Lateral MOSFETs) which should tell you all the information you need to know. They can be purchased from Lateral MOSFETs - Class-d Limited should you take an interest to them.
If you have any questions at all we will be more than happy to help you. The best thing to do is speak to our technical director (Mike) on 07980 600 373 and he will be able to tell you everything you need to know. Alternatively, you can drop him an email mike@proaudio.ltd.uk and he will get back to you shortly.
Best of luck,
Pro Audio Ltd
Ive been interested in these, and have been looking for datasheets, is any available as yet.
I find the toshiba vertical mosfets to sound better than the irf parts and by quite a margin, if used in the same application, measured performance is also superior with the toshibas, price is a problem tough.
When it comes to laterals which I prefer over vertical types Im still in the cold, how I miss the old 2sj50 and 2sk135, the newer 2sk1058 and compl just doesnt sound the same. Ive had to use the newer parts to repair a channel of a amp I built as a teenager and one can clearly hear a difference between the 2 channels.
When it comes to laterals which I prefer over vertical types Im still in the cold, how I miss the old 2sj50 and 2sk135, the newer 2sk1058 and compl just doesnt sound the same. Ive had to use the newer parts to repair a channel of a amp I built as a teenager and one can clearly hear a difference between the 2 channels.
True, but as you know, the best way not to have a problem is not to correct it when it's there, but not to have it in the first place. This sort of thing tends to result in abuse of NPV. One other possibility would be to put a source resistor on the IRFP240, but not on the 9240. Or, simply, use IRFP340 instead of IRFP240. My point is, know thy MOSFETs
This is quite true, and a trick some are unaware of. When talking complementary, better matching is good, but one must also say in what characteristic. It is fundamentally very difficult, given the physics, to have N and P channel MOSFETs matched in every regard. This is also true of BJTs and the sex of most human beings.
Nevertheless, if you know what you are doing, superb results can be had with MOSFETs like the IRFP240/9240. At about three times the price, the Toshiba devices are indeed somewhat better.
BTW, going quasi comp just because you can get both devices to be N-type is silly because the quasi comp output stages are fundamentally asymmetrical. Most BJT designers left the quasi comps behind nearly 40 years ago.
Cheers,
Bob
This is the datasheet for the ALFET Lateral MOSFETs. If you need any more information, please give the office a ring on 01623 654080 and someone will be able to help you out.
http://www.lateralmosfet.com/Lateral Mosfet Datasheet.pdf
Kind Regards,
Pro Audio
How are these MOSFETs unique? They look like they're based on the Hitachi laterals from many years back. Also how are they "much better" than other FETs when the application circuits you show in your datasheet only achieve distortion of <0.07% ?
I would like to know why the Class D /Pro Audio Alfet mosfets seem to have an higher claimed current rating than the other Semelab Alfet mosfets from Magnatec
Single die
http://www.semelab.com/pdf/magnatec/ALF08N16V ALF08N20V.pdf
Double Die
http://www.semelab.com/pdf/magnatec/ALF16N16W ALF16N20W.pdf
or Profusion
Double Die
http://www.profusionplc.com/images/data sheets/ecw20n20-z.pdf
Or are Class D Claiming that their Alfet Semelab Mosfets are somehow different to the Other alfet Semelab Mosfets that are available??????????.
Profusion is now listing the Alfet type mosfets as available but they don't call them Alfets.
Magnatec are supplying spec shets for alfet mosfets but I don't know about availbility.
from MagnatecSingle die
http://www.semelab.com/pdf/magnatec/ALF08N16V ALF08N20V.pdf
Double Die
http://www.semelab.com/pdf/magnatec/ALF16N16W ALF16N20W.pdf
or Profusion
Double Die
http://www.profusionplc.com/images/data sheets/ecw20n20-z.pdf
Or are Class D Claiming that their Alfet Semelab Mosfets are somehow different to the Other alfet Semelab Mosfets that are available??????????.
Profusion is now listing the Alfet type mosfets as available but they don't call them Alfets.
Magnatec are supplying spec shets for alfet mosfets but I don't know about availbility.
Toshibas are not 3 times the price if you buy in sufficient quantities.
More like 1.5-2x to IRFP240 at the same quantities (>>100).
If you have a fully symmetrical design that require true complementaries, then for me there are no better devices.
Hitachi laterals just don't have enough transconductance.
If you parallel more to make that up, then they are really expensive.
Semelabs are expensive and not (much) better, if at all.
Patrick
More like 1.5-2x to IRFP240 at the same quantities (>>100).
If you have a fully symmetrical design that require true complementaries, then for me there are no better devices.
Hitachi laterals just don't have enough transconductance.
If you parallel more to make that up, then they are really expensive.
Semelabs are expensive and not (much) better, if at all.
Patrick
It has been a long time but i say that 2sk3497 is good at transconductance but it has 2,5 times more input capacitance than 2sk1530 and it may cause reducing at high frequencies.
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