No. I am sorry not to review the circuit (312). I have offered, for free, the circuit that works and I can guarantee its proper function. Anyway, I cannot go through the half-cooked ideas and try to fix it.
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Thanks Mooly - I see this is available from my usual source at $3.28 if I buy 10.
Thanks Pavel! two of these are available from my usual source
IRFP90N20D 200V 0.023ohm 94A - $4.55
IRFS59N10D 100V 0.025ohm 59A - $2.53
I also found this, but there are concerns about it not being a major manufacturer ?
IPD200N15N3G 150V 0.020ohm 50A- $2.51
and of more 'repute'
IRFB4227PBF 200V 0.024ohm 65A - $2.89
I have installed clamping diodes to the output of the amplifier already, reverse biassed across the emitter-collectors of each BJT output device - is this what you are referring to ?
Yes - you are correct !
A look at the data sheet for the part I suggested does indeed show the need for this resistor. They also have a part with the resistor included inside the package but alas that version is not available from my usual source. I've attached the relevant section from the datasheet.
I would agree, but there is the danger of higher voltages when interrupting current flow through inductive speaker.
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Do you know what? I really empathize with Pavel. You guys are just hounding him unneccessarily. Just quit all this paranoid s**t and build it yourself. Then test it yourself and then thank him for a great design, or if it fails - which it hasn't yet - then fix it yourself. It's a gift for heavens sake. Accept it with gratitude.
There are too many parasitic members hiding in the woodwork of this forum, and they think that they are immune to all the social norms, well guess what, she's a small world out there fellows.
I am guilty too, but one thing is for sure, we all spend too much time on the computer and not enough time backing up the talk talk with real product.
Not at all impressed.
sincerely, Phil E.
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Nobody is hounding anybody. There isn't really any obligation for people to build and test and 'back up their talk with any real products' - this is a hobby forum and some people enjoy talking about design without building or are unable to build due to personal circumstances. You are a man of action, I've seen your builds, but not everyone is as active
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This correct. Most mosfets (especially the Trench technology ones) are rated for inductive load dump. You can calculate the energy from your speaker and cabling inductances and the peak current. Typically the channel will avalanche at 5 to 10 percent above the rated Vds.
"I have installed clamping diodes to the output of the amplifier already, reverse biassed across the emitter-collectors of each BJT output device - is this what you are referring to ?"
I think they are on the wrong side of the relay. I don't know if the FETs can take a multi-hundred volt inductive shot from fly-back energy without the D5, D6 diodes.
I think they are on the wrong side of the relay. I don't know if the FETs can take a multi-hundred volt inductive shot from fly-back energy without the D5, D6 diodes.
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I also have fuses in the rails. I have fuses in the collector leads for the output power transistors and fuses back at the PSU in each rail (rated slightly lower than those next to the power devices).I always use a relay in series with the speaker and fuses in the supply lines(after the caps. in series with the amp.) for each amp. Never had any prob. If something would happen the fuses blow and the relay switches off. Painless
good, as I'm leaning heavily towards use of IPD200N15N3 which I have a need to order some shortly
Thanks! - I will ensure I have clamp diodes before and after.
* The Resistor *
==========
Looking at the value of the resistor I need to place between the FET gates in order to help discharge the gates during turn off - there is a trade-off between the desire for it to be small for high speed but not so small as to load down the opto-isolator.
The chosen opt can provide 12uA into a short and 7V into an open circuit. I figure this can be crudely thought of as a battery with internal resistance of 580k. The gate discharge resistor will load down the output so that it is no longer able to reach 7V. Therefore, the resistor must be large enough so that the voltage at the output of the opt is still sufficient to turn the FETs hard-on. I figure 5V is a safe value which requires a load resistor of around 1.5meg.
To turn off the FETs the resistor must discharge the gates to below the threshold voltage which I'll take as worse case 2V. The voltage will roughly fall off exponentially, the time constant is equal to RC and the voltage will fall by a factor of 'e' or roughly 2.71 during this time. We only need one time constant to turn off the FETs.
I'll take a worse case total gate + wiring capacitance of 4,000pF per gate then with two devices we have to discharge a total of 8nF through 1.5meg. This means the turn-off time will be around 12ms.
Sound reasonable ?
Some more philosophy.
I got a bit excited last night because there seems to be a lot of one way traffic on some of the DIY forums. I also used some provocative terms for which I would like to apologise. I am sorry for upsetting the status quo.
As Bigun told me in an ensuing post "it is only natural that we want to know more and ask a question or two". That is just normal and I do it too.
On the other hand, at times we just have to accept that things are the way they are when it comes to complicated issues like these.
A philosophy that has served me well in the past is known to some as "Suck it and see" - (SIAS), meaning that you just wont know how it will go until you actually give it a go.
The process of giving it a go, sheds light on the inherent nature of a problem, weather it be thickening a stew or building a Jacobs Ladder the same SIAS principal applies and reveals techniques that are learnt in the process. 'Natural Learning'.
Bigun also made the comment that some members may not wish to build or are incapable of building and with these people I truly sympathise, because those people obviously lack imagination, motivation or both.
By this I mean, If you cant, or dont want to build electronics; Then why not try something else? Why even join a forum dedicated to doing just this, -i.e. DIY or Do It Yourself.
I will give you an example of what I am driving at:
I have some arthritus in my fingers and before too long I may not be able to hold a soldering iron. If and when this happens I will have achieved enough to finally let go. But for me to let go simply means that one door closes whilst another opens.... Perhaps I will write a novel, I just dont know.
I can't reply to all of the mail I received last night because I am going to build Pavel's circuit with some different components sourced from the tip! If I keep trying honestly and dont give up I should have a result by Friday. If not, I'll have to revert to the bad old fuse.
PS. I would like you all to take a look at post #333 it shows that at least to some extent, the man probably felt a bit overwhelmed by our response.
Cheers and bye for now, Phil E.
I got a bit excited last night because there seems to be a lot of one way traffic on some of the DIY forums. I also used some provocative terms for which I would like to apologise. I am sorry for upsetting the status quo.
As Bigun told me in an ensuing post "it is only natural that we want to know more and ask a question or two". That is just normal and I do it too.
On the other hand, at times we just have to accept that things are the way they are when it comes to complicated issues like these.
A philosophy that has served me well in the past is known to some as "Suck it and see" - (SIAS), meaning that you just wont know how it will go until you actually give it a go.
The process of giving it a go, sheds light on the inherent nature of a problem, weather it be thickening a stew or building a Jacobs Ladder the same SIAS principal applies and reveals techniques that are learnt in the process. 'Natural Learning'.
Bigun also made the comment that some members may not wish to build or are incapable of building and with these people I truly sympathise, because those people obviously lack imagination, motivation or both.
By this I mean, If you cant, or dont want to build electronics; Then why not try something else? Why even join a forum dedicated to doing just this, -i.e. DIY or Do It Yourself.
I will give you an example of what I am driving at:
I have some arthritus in my fingers and before too long I may not be able to hold a soldering iron. If and when this happens I will have achieved enough to finally let go. But for me to let go simply means that one door closes whilst another opens.... Perhaps I will write a novel, I just dont know.
I can't reply to all of the mail I received last night because I am going to build Pavel's circuit with some different components sourced from the tip! If I keep trying honestly and dont give up I should have a result by Friday. If not, I'll have to revert to the bad old fuse.
PS. I would like you all to take a look at post #333 it shows that at least to some extent, the man probably felt a bit overwhelmed by our response.
Cheers and bye for now, Phil E.