Overshooting, ringing and blowing up mosfets if you build stuff based on irresponsible advice - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Closed Thread
 
Thread Tools Search this Thread
Old 25th July 2003, 07:09 PM   #1
diyAudio Retiree
 
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Default Simple is as simple does........

"Steve: That is ultimate simplicity!"

http://www.diyaudio.com/forums/attac...&postid=213170

Hmmm.......... A high inductive transformer winding and a highly capacitive mosfet gate with no damping or voltage clamps. Yep, that is about the simplest designer that I have seen here.
 
Old 25th July 2003, 07:23 PM   #2
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Default Re: Simple is as simple does........

Quote:
Originally posted by Fred Dieckmann
"Steve: That is ultimate simplicity!"

Hmmm.......... A high inductive transformer winding and a highly capacitive mosfet gate with no damping or voltage clamps. Yep, that is about the simplest designer that I have seen here.
No damping? What, did Jensen discover room temperature superconductors and are using them to wind their transformers unbeknownst to everyone else?

And what highly inductive transformer winding? The only inductance the input capacitance of the MOSFET would see is the small amount of leakage inductance, which is in series with the non-resistance of those superconductive windings.

se
 
Old 26th July 2003, 10:10 AM   #3
diyAudio Retiree
 
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Default Where did supercondutors come into this?

"No damping? What, did Jensen discover room temperature superconductors and are using them to wind their transformers unbeknownst to everyone else?

And what highly inductive transformer winding? The only inductance the input capacitance of the MOSFET would see is the small amount of leakage inductance, which is in series with the non-resistance of those superconductive windings.

se"

"Not if they're loaded properly. The Jensen JT-13K7-A which is a 1:5 step-up has a flat response across its bandwidth, which is from 0.9Hz to 120kHz."


I am sorry I thought anyone would know I was taking about adding external damping resistor, especially you after the loading statment. BTW it would only see solely leakage inductance with the primary shorted Perhaps you tell us the resistive component of the leakage inductance ( actually it would be a a leakage impedance if it is an RL circuit as you stated) and tell us the resonant frequency it will from with the mosfet capacitance and the resulting Q of that circuit . It couldn't possibly be a high Q circuit that will ring like hell, could it? Pure idle speculation of my part I'm sure. Isn't this the same guy that puts a snubber on the secondary of his isolation transformers? The number times the recommendation for putting gate damping resistors on Fets has been posted here (usually by Mr. Pass) is in the double digits. Gate damper resistors are a good idea for even wiring inductance resonating with gate capacitance and oscillating. I thought you knew a lot about transformers and capacitive loading. I apologize, I won't make that mistake again. It will probably only oscillate or overshoot long enough to punch through the Mosfet gate dielectric and destroy the transistor and stop any oscillation, or amplification. Be sure to DC couple the output for further parts saving, you're speaker won't mind the resulting DC in a fault condition described above. I suppose this is just a matter of opinion though. You would never risk offering advice on a subject that was beyond your understanding and could result in an amplifier blowing up from building such a circuit.

I will however apologize sincerely for the statement:

"Yep, that is about the simplest designer that I have seen here."

It was supposed to read:

"Yep, that is about the simplest DESIGN that I have seen here."

It was sloppiness and haste. I had no intention of stating or even implying ( for the many that read between the lines on this forum) that you were a simpleton. Thanks for not taking offense at my carelessness.

mea culpa,
Fred
 
Old 26th July 2003, 06:00 PM   #4
diyAudio Retiree
 
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Default There's been some hard feelings here About some words that were said

If I may reflect a bit on the subject at hand......

"You're looking at it backwards. A 1:9 step-up transformer doesn't reflect the load back to the source by a factor of 81, but a factor of 1/81 (looking back from the load to the source it's a step-down transformer). It's the source that gets reflected to the load by a factor of 81."


Reducing the impedance by a factor of the 81 is the the same thing as increasing the capacitance by the same factor.
http://w1.859.telia.com/~u85920178/begin/calc-00.htm
Reactance of a Capacitor
Formula: Reactance = 1 / (2 * Pi * F * C)



When you look into one winding the load on the secondary winding relflects by the square of the turns ratio. That's why the call them step up or step down transformers and why the distinction is
one of which side your looking into.

http://www.bowest.com.au/library/machines.html#01

The primary circuit impedance Z1 referred to the secondary circuit for an ideal transformer with N1 primary turns and N2 secondary turns is:
Z12 = Z1(N2 / N1)2

The secondary circuit impedance Z2 referred to the primary circuit for an ideal transformer with N1 primary turns and N2 secondary turns is:
Z21 = Z2(N1 / N2)2

As Paul Simon said "One man's ceiling is another mans floor"

Have I told you how much we have missed you. I usually have to pay money for entertainment and education like this. but the truth will set you free.

Yeah we tease him a lot cause we've got him on the spot, welcome back,
Fred
 
Old 26th July 2003, 06:35 PM   #5
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Default Re: Where did supercondutors come into this?

Quote:
Originally posted by Fred Dieckmann
I am sorry I thought anyone would know I was taking about adding external damping resistor, especially you after the loading statment.
I know you were talking about an external damping resistor. But you said there was no damping. To wit:

A high inductive transformer winding and a highly capacitive mosfet gate with no damping or voltage clamps.

In order for that to be the case, the secondary would have to have been wound with some sort of resistanceless superconductive wire.

Point being, there's damping built-in in the form of the secondary's winding resistance, which in the case of the transformer I had in mind, is about 470 ohms.

Quote:
BTW it would only see solely leakage inductance with the primary shorted
The only other inductance it would see would be any inductance from the source, which would typically just be the inductance of the interconnects.

Quote:
Perhaps you tell us the resistive component of the leakage inductance ( actually it would be a a leakage impedance if it is an RL circuit as you stated)...
The resistive component would be the secondary winding resistance which again in this case is 471 ohms. Of course the source resistance also becomes part of this.

Quote:
...and tell us the resonant frequency it will from with the mosfet capacitance and the resulting Q of that circuit . It couldn't possibly be a high Q circuit that will ring like hell, could it?
Don't see how it could be with such a small amount of inductance and a large amount of resistance. Certainly there will be some resonance, but I don't see how it could have a terribly high Q.

Quote:
Pure idle speculation of my part I'm sure.
Well, I think you could stand to brush up a bit on transformer basics.

Quote:
Isn't this the same guy that puts a snubber on the secondary of his isolation transformers?
Yes, but it's optional. Some people freak if there's any deviation from objective perfection.

Quote:
The number times the recommendation for putting gate damping resistors on Fets has been posted here (usually by Mr. Pass) is in the double digits.
The damping is there. It's just not written out literally in the idealized schematic.

Quote:
Gate damper resistors are a good idea for even wiring inductance resonating with gate capacitance and oscillating.
But in that case, the ratio of the inductance to wire resistance is much smaller. In the case of a transformer's secondary, the ratio of the winding resistance to the leakage inductance is far far greater.

Quote:
I thought you knew a lot about transformers and capacitive loading. I apologize, I won't make that mistake again.
And I thought you knew at least a little something about transformers. I apologize. I won't make that mistake again.

Quote:
It will probably only oscillate or overshoot long enough to punch through the Mosfet gate dielectric and destroy the transistor and stop any oscillation, or amplification.
Christ. Get a grip on yourself, Fred.

Quote:
Be sure to DC couple the output for further parts saving, you're speaker won't mind the resulting DC in a fault condition described above.


Quote:
I suppose this is just a matter of opinion though. You would never risk offering advice on a subject that was beyond your understanding and could result in an amplifier blowing up from building such a circuit.
I understand that the leakage inductance is quite small and winding resistance quite high. And I wasn't the the one effectively claiming that transformers have zero winding resistance and therefore no damping.

se
 
Old 26th July 2003, 09:16 PM   #6
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Default Re: There's been some hard feelings here About some words that were said

Quote:
Originally posted by Fred Dieckmann
Reducing the impedance by a factor of the 81 is the the same thing as increasing the capacitance by the same factor.
http://w1.859.telia.com/~u85920178/begin/calc-00.htm
Reactance of a Capacitor
Formula: Reactance = 1 / (2 * Pi * F * C)
Aye. Oversight on my part.

Quote:
Have I told you how much we have missed you. I usually have to pay money for entertainment and education like this. but the truth will set you free.
Just returning the favor. I'd have never known that transformer manufacturers were now using room temperature superconducting wire. Thanks for bringing me up to speed on that one.

se
 
Old 27th July 2003, 12:01 AM   #7
Account Disabled
 
Join Date: Apr 2003
Location: US
Default Re: Re: There's been some hard feelings here About some words that were said

Quote:
Originally posted by Steve Eddy
Just returning the favor. I'd have never known that transformer manufacturers were now using room temperature superconducting wire. Thanks for bringing me up to speed on that one.

se

that's a funny one.

Didn't I say that if you listen to Fred long enough, you will sure pick up a scientific breakthrough sooner or later,
 
Old 27th July 2003, 12:13 AM   #8
diyAudio Retiree
 
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Default Thanks for bringing me up to speed on that one.

Not at all. For guy who wants talk about parasitics like leakage inductance, you should probably learn the basics equations for reflected impedance first. Leakage inductance is distributed parameter like winding capacitance and not accurately described by a simple lump element leakage inductance term in an idealized model of a transformer. The reflected impedance from the primary is complex impedance and a function of the source impedance and the interconnect which is a transmission line and not a simple inductance and capacitance. I have worked on pulse transformer design with compensation networks and EMI reduction on switching power supplies. But you would rather talk about superconductors and idealized models that you don't even have the basics down for. Thanks for the advice on transformer basics. You know I would even have a problem discussing this with someone who knew something about the subject, but to be second guessed someone who has barely dipped his toe into some pretty complicated design issues is just priceless......... A little knowledge is a dangerous thing. A very little knowledge with pretensions of being an expert, well that is true humor that I enjoy beyond description. That is why I read this forum, for just such moments of transcendental absurdity. I just pray the Jocko doesn't read this until the next time he comes over, so I can watch him roll around on the floor in hysterics. thanks for straighting me out on about ten years engineering misperceptions, including a failure to understand any of the half a dozen books I have read on magnetics, the computer models, and the time domain reflectometry measurements. Thanks again for your breathtaking efforts to entertain and educate us. I wouldn't have it any other way.

One of your biggest fans,

Fred
 
Old 27th July 2003, 01:35 AM   #9
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Fred, why do you even bother educating Rita?

Cheers,
__________________
Frank
 
Old 27th July 2003, 03:24 AM   #10
diyAudio Member
 
Steve Eddy's Avatar
 
Join Date: Sep 2002
Location: Sacramento, CA
Default Re: Thanks for bringing me up to speed on that one.

Quote:
Originally posted by Fred Dieckmann
For guy who wants talk about parasitics like leakage inductance, you should probably learn the basics equations for reflected impedance first.
I'm well aware of the basic equations for reflected impedance. My error was one of laziness and not thinking through and realizing that where a purely capacitive load is being considered, reducing the load impedance by a factor of 81 is the same as increasing capacitance by the same factor.

Quote:
Leakage inductance is distributed parameter like winding capacitance and not accurately described by a simple lump element leakage inductance term in an idealized model of a transformer.
What!?

Lumped parameters are just fine until the system size starts approaching 1/4 wavelength of the shortest wavelength you plan on passing thruogh the system or the system is capable of passing. Seeing as we're talking about audio here, even considering an unusually sluggish propagation velocity of 50% C, at 20kHz we're talking about a wavelength of about 5 miles, 1/4 of that being a little over a mile.

And by the way, leakage inductance and winding capacitance aren't part of the idealized model. That's why it's called an idealized model.

Quote:
The reflected impedance from the primary is complex impedance and a function of the source impedance and the interconnect which is a transmission line and not a simple inductance and capacitance.
Still boils down to the lumped inductance and capacitance at audio frequencies.

Quote:
I have worked on pulse transformer design with compensation networks and EMI reduction on switching power supplies.
So? This is audio. We're not trying to pass narrow 100kHz pulses through the system.

Quote:
But you would rather talk about superconductors and idealized models that you don't even have the basics down for.
You apparently don't even know what an idealized model is. Or for that matter what the word idealized means. When you start adding parasitics, it's no longer an idealized model. So when I'm talking about leakage inductance and winding resistance and capacitance, I'm clearly not talking about the idealized model.

se
 

Closed Thread


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
ringing of mosfets in UcD simulation zilog Class D 9 21st December 2006 02:19 PM
Ringing Mosfets Rog Solid State 1 2nd March 2004 09:21 PM


New To Site? Need Help?

All times are GMT. The time now is 09:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2