SD2000 Installing a better FET

[Unregistered]

The FET should not be getting hot, when testing my 2000 the FET can run warm but not hot unless I have shorted the case to the positive ground!! When I was designing the PI back it '99 I had a similar problem, at first the engineer said that maybe the switching wasn't real square-waves, I found out it was the damping resistor. Changed that and no more hot FET. I would say that the FET is just not compatible enough. Stick with the 840 can't really see what you would gain with the one you are using now. A FET should not get real hot if everything is designed to suit it. You could do like I did and change the dampening resistors (remember they use 12+ in the 2000!)

Regards Ismael
www.minelabmods.com

Your engineer was right, minelab isn`t it,...they incorporate some sine wave so the "edges" are "rounded off".

[Sean_Goddard]

Like a scope calibration signal when the probe is misaligned due to poor frequency response?

I think it's not incorporation of SIN waves, but extraction, due to slew rate limited driving, and as we all know a FET ONLY dissipates power whilst it is switching, so..The faster you switch it, the cooler it will run. Sharpen up the edges of the Tx drive and the whole thing will be much more efficient, BUT.. I suspect Mr. Candy has a reason for limiting this rise time, perhpas to stop RF QRM (interference) to meet with CE approval OR maybe just to slow the current build up for some other reason. Maybe circuit inadeqacies elsewhere?

[JC1]

Eric Foster

Like a scope calibration signal when the probe is misaligned due to poor frequency response?

I think it's not incorporation of SIN waves, but extraction, due to slew rate limited driving, and as we all know a FET ONLY dissipates power whilst it is switching, so..The faster you switch it, the cooler it will run. Sharpen up the edges of the Tx drive and the whole thing will be much more efficient, BUT.. I suspect Mr. Candy has a reason for limiting this rise time, perhpas to stop RF QRM (interference) to meet with CE approval OR maybe just to slow the current build up for some other reason. Maybe circuit inadeqacies elsewhere?

Hi Sean,

Slow current build up because the dI/dT is what

induces current into the target. As Eric Foster has

explained to everyone the current induced on the

turn on can somewhat cancel out the turn off if not

given time to die out before turn off. The slow rise

in current would induce less current to start with

and hench less to die down. Sawtooth looking waveform.

Just a guess, I don't know what Candy was really up to.

[Qiaozhi]

Hi Sean,

Slow current build up because the dI/dT is what

induces current into the target. As Eric Foster has

explained to everyone the current induced on the

turn on can somewhat cancel out the turn off if not

given time to die out before turn off. The slow rise

in current would induce less current to start with

and hench less to die down. Sawtooth looking waveform.

Just a guess, I don't know what Candy was really up to.

Hi JC1,

I have a question for you that's not related to this thread: Why are all your posts double-spaced with short lines??

[gef12]

Hi JC1,

I have a question for you that's not related to this thread: Why are all your posts double-spaced with short lines??

[JC1]

Good Question

Hi JC1,

I have a question for you that's not related to this thread: Why are all your posts double-spaced with short lines??

Hey that is a good question.

Don't know why.

Just are.

Funny.

[Qiaozhi]

Hey that is a good question.

Don't know why.

Just are.

Funny.

Are you on a Linux machine by any chance, or using FireFox or something similar?

[JC1]

hey

It is a windows machine but i have been using firefox but have netscape and even window ie crap that i don't use no more. Hey, just cause everybody else has been conditioned to follow societies norms, don/t mean i has too. i got out of the box, long time ago,

really

[Qiaozhi]

It is a windows machine but i have been using firefox but have netscape and even window ie crap that i don't use no more. Hey, just cause everybody else has been conditioned to follow societies norms, don/t mean i has too. i got out of the box, long time ago,

really

So you only

post this way

to be different.

[Mr. Bean]

Am different

Hi Qiaozhi,

No I really am different.

I was born on a farm.

Help me.

I was born on a farm.

Really

Rowan Atkinson was born on a farm in Durham on January 8th, 1956. He got his Electrical engineering degree on Oxford university. His comedy career started at the Edinburgh fringe. He was also a late member of "Monty Python".

http://www.geocities.com/TelevisionCity/5349/biogra.htm

[gef12]

Yes he only posts this way to be different and stand out in the crowd
we all knows that

[Mr. Bean]

Wacko

Yes he only posts this way to be different and stand out in the crowd
we all knows that

I think the guy is wacko myself.

He was posting double space two years ago.

I think he is wacko.

Look.

https://www.geotech1.com/thuntings/s...ad.php?t=11065

Hi Eric,

Hope you're getting this.

Part of Classwork.

There will be a test.

Performance.

So build it yourself, lots of time, hmmmm, Receipe.

Take a 1.0 nV/rtHz or less JFet, add a drain resistor, add opamp, close loop on whole thing.

No not that easy, but not that bad either.

Good start?

[Sean_Goddard]

Noisama what now???

OK I can follow those calculations but they make my head hurt. I just know what works and what don't, WHY it don't is usually based on experience, but it's nice to see the math now and again.

BTW I sometimes post double spaced. If I try to post HTML then it happens that way. Glitch in forum coding I guess.

[Mr. Bean]

Math

Noisama what now???

OK I can follow those calculations but they make my head hurt. I just know what works and what don't, WHY it don't is usually based on experience, but it's nice to see the math now and again.

BTW I sometimes post double spaced. If I try to post HTML then it happens that way. Glitch in forum coding I guess.

I like the Math. With Math Man went to the Moon.

And returned safely. Many times. Analyzed to pieces.

Without Math. Man had big ideas.

Like shoot self to Moon out of big Canon.

Not good idea.

[Max]

I like the Math. With Math Man went to the Moon.

And returned safely. Many times. Analyzed to pieces.

Without Math. Man had big ideas.

Like shoot self to Moon out of big Canon.

Not good idea.

Hi,
ehm yes... sure... but but but... math said also that probability of a "safe" land & return was 50% for Apollo11 after spent $24 billion

not a big result from my point of view...

The onboard computer of Apollo11-lander (LEM) had a serious problem just during the landing and manual controls must be used by Armstrong to compensate the error and find on the fly a "possible" landing surface with his eyes (not math) between big-stones and a crater and they spent about all the residual fuel just when the lander touched the Moon... big math calculations... oh yeah !

They were lucky on the Moon... cause if you look also at Apollo1 on-pad-fire and Apollo-13 on-board explosion you'll get the picture that no math can avoid disasters when things get too complex and you are in a hurry.

So the Moon program success was math success too ? ... uhm... maybe... but I think not only.

Kind regards,
Max