Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

Not directly.

You'll need some level translation.

If you don't know what that means then you shouldn't be attempting to make a
welder.

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Graham

Pooh Bear wrote:
Ignoramus965 wrote:


My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?


Not directly.

You'll need some level translation.

If you don't know what that means then you shouldn't be attempting to make a
welder.

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Graham


There's quite a bit of gate capacitance in larger MOSFETS that has to be
quickly filled or emptied. Drivers are by no means trivial.

In fact, the design of the driver stage is usually much more difficult
than the output stage.


--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email:

Please visit my GURU's LAIR web site at http://www.tinaja.com

Ignoramus965 wrote:

On Fri, 09 Sep 2005 04:34:10 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

Not directly.

You'll need some level translation.

do you refer to signal voltage level?

If you don't know what that means then you shouldn't be attempting to make a
welder.

I would love to hear you share your knowledge.

i

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Graham

Ignoramus965 wrote:

Don, what are your thoughts on using IGBT's for switching?

Graham replies that they're very good these days.

Mosfets are best at the higher frequencies though.

IGBTs have their own little 'quirks'.

trouble is.... you really have to have been doing this stuff for ages to pick up
the relevant issues. For a beginner, jumping in at the deep end involves a
cliff-like learning curve.

Graham

Ignoramus965 wrote:

There's quite a bit of gate capacitance in larger MOSFETS that has to be
quickly filled or emptied. Drivers are by no means trivial.


Don, what are your thoughts on using IGBT's for switching?

Oh, boy! Now, you're REALLY getting in deep water!

The FETs are a lot more forgiving of shorts and linear operation, and
at the voltages you are looking at, they work a lot better, too.

But, still, you need perhaps 2-3 A of gate current for EACH FET in
your circuit! If you put 5 in parallel, you need 10-15 A of gate
current to charge the gates. Now, that is only for 50 nS or so,
then the current in the gate drops to zero. But, if you don't
provide this kind of current, the transistor will burn up in the
linear region before it ever gets fully turned on.

With IGBTs, if they are ever allowed to operate in the linear region,
even for a hundred nS, they are destroyed! The FETs have what is
called negative temperature coefficient, when they get hot, the
current they will conduct drops. This allows them to distribute
current evenly across the transistor, and across multiple transistors,
even when in the linear region. IGBTs flatten out in the saturation
region, but have a strong POSITIVE temp coeff. in the linear region.
Current will "hog" to the hottest part of the transistor die in the
linear region, and the transistor will self-destruct.

So, you really want to avoid the IGBT.

And, you will not be able to use your signal generator because it
can't provide several amps. You could do a low-power test, maybe
lighting an LED with it, to see the rise-times, etc. on your
scope.

For an H bridge, you need 4 different gate drives. Two of them
can be ground-referenced, but two of them (for the "high-side"
transistors) will have to be floating. You don't want to use
complementary transistors, ie. P channel, as they have MUCH lower
performance than N channel. So, using all N channel, the high side
transistors have their source connected to the floating output
terminal. So, the gate driver must supply gate voltage referenced
to the floating output voltage.

The IR 2113 and related chips can handle much of this stuff for
you.

One final problem is the DC welder will have a huge inductor at the
output. Thus, the output will probably have large voltage excursions
when the electrode touches the workpiece and the arc starts. So, you
can't depend on getting a steady 40 V DC or whatever. When the arc
breaks or sputters, you may have hundreds of Volts on the electrode
cable. I think the standard practice is to move the inductor to the
electrode cable AFTER the switching circuit. But, the design of
the welder may make this hard to do. Certainly in AC "buzz box"
welders, the output inductance is just built into the transformer,
it is not a separately-connected coil. I guess they can't do that
in a DC welder, so you may be able to change the connection there.

Jon

Ignoramus965 wrote:

On Fri, 09 Sep 2005 05:07:38 +0100, Pooh Bear wrote:

Ignoramus965 wrote:

On Fri, 09 Sep 2005 04:34:10 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

Not directly.

You'll need some level translation.

do you refer to signal voltage level?

If you don't know what that means then you shouldn't be attempting to make a
welder.

I would love to hear you share your knowledge.

i

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Thanks. I just read their spec sheet. Is there some other document
that you have in mind?

I can think of loads ! You can't imagine how many data sources I used before venturing into this
arena.

You need to examine the application notes really.

The ANs normally contain 'nuggets of wisdom' worth as much or more than gold.

Graham

Pooh Bear wrote:
Ignoramus965 wrote:


Don, what are your thoughts on using IGBT's for switching?


Graham replies that they're very good these days.

Mosfets are best at the higher frequencies though.

IGBTs have their own little 'quirks'.

trouble is.... you really have to have been doing this stuff for ages to pick up
the relevant issues. For a beginner, jumping in at the deep end involves a
cliff-like learning curve.
Yeah, like hanging on the cliff while the enemy is strafing you!
Actually, that is being showered by incandescent particles of your
expensive IGBTs, right after the cannon-like bang when they explode!
I know, I've been there. The last inverter design I worked on, I
had two glowing IGBTs shoot past my head on either side. After that,
I took to powering the thing up while crouching under the table with
ear protectors on. Once it survived power-up, I got up and looked at
the picture on the scope with a lot less fear.

I told all this stuff about keeping out of the linear region, etc.
to a guy working on a hybrid electric car drive, but he had to do
it his way! He ended up with a Ford Taurus wagon filled with batteries
almost doing a wheelie inside a garage full of people when the IGBT
popped!

Jon

On Fri, 09 Sep 2005 05:07:38 +0100, the renowned Pooh Bear
wrote:


Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Graham


Better read the application notes really carefully too. What you don't
know will fry expensive semiconductors, typically a few at a time.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Spehro Pefhany wrote:

On Fri, 09 Sep 2005 05:07:38 +0100, the renowned Pooh Bear
wrote:

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Graham

Better read the application notes really carefully too. What you don't
know will fry expensive semiconductors, typically a few at a time.

Best regards,
Spehro Pefhany

Trouble is....

Even when you do know it, you're likely to fry several by accident for good measure anyway !

Fzzztttzzzzzzttt ! poPPPP ! BANG !!

Graham ;-)

Ignoramus965 wrote:

On Fri, 09 Sep 2005 05:32:36 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

On Fri, 09 Sep 2005 05:07:38 +0100, Pooh Bear wrote:

Ignoramus965 wrote:

On Fri, 09 Sep 2005 04:34:10 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

Not directly.

You'll need some level translation.

do you refer to signal voltage level?

If you don't know what that means then you shouldn't be attempting to make a
welder.

I would love to hear you share your knowledge.

i

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Thanks. I just read their spec sheet. Is there some other document
that you have in mind?

I can think of loads ! You can't imagine how many data sources I used before venturing into this
arena.

You need to examine the application notes really.

The ANs normally contain 'nuggets of wisdom' worth as much or more than gold.

Thanks. I will read them closely tomorrow, when I print that document
out.

That said, can I get some intro on how these chips are used? Are they
connected to DC power (for sending signals to MOSFETs), as well as to
a signal generator that "drives" the chip? How do I tell the chip what
to do?

Is that big enough for a 12 kW power transmission device, or is it
just an example?

I apologize if this question is answered in application notes.

So many issues !

When you've read a few ANs about gate drivers pop back in and ask again.

Ohh - and you do know about how to control circulating currents in pcbs ?

Graham

Ignoramus965 wrote:

On Fri, 09 Sep 2005 06:05:45 +0100, Pooh Bear wrote:

Ignoramus965 wrote:

On Fri, 09 Sep 2005 05:32:36 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

On Fri, 09 Sep 2005 05:07:38 +0100, Pooh Bear wrote:

Ignoramus965 wrote:

On Fri, 09 Sep 2005 04:34:10 +0100, Pooh Bear wrote:
Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

Not directly.

You'll need some level translation.

do you refer to signal voltage level?

If you don't know what that means then you shouldn't be attempting to make a
welder.

I would love to hear you share your knowledge.

i

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term 'high side drive'.

Thanks. I just read their spec sheet. Is there some other document
that you have in mind?

I can think of loads ! You can't imagine how many data sources I used before venturing into this
arena.

You need to examine the application notes really.

The ANs normally contain 'nuggets of wisdom' worth as much or more than gold.

Thanks. I will read them closely tomorrow, when I print that document
out.

That said, can I get some intro on how these chips are used? Are they
connected to DC power (for sending signals to MOSFETs), as well as to
a signal generator that "drives" the chip? How do I tell the chip what
to do?

Is that big enough for a 12 kW power transmission device, or is it
just an example?

I apologize if this question is answered in application notes.

So many issues !

When you've read a few ANs about gate drivers pop back in and ask again.

Ohh - and you do know about how to control circulating currents in pcbs ?

Thanks. I will spend quite a while reading that stuff. That said, all
I find are spec sheets. Is there some secret location for application
notes, say for the IR 2113 driver?

Look Sonny ! All the semi makers write app notes about how to use their products best so that they can
hopefully sell more of them !

I have no trouble finding the ANs. Why do you ?

Try 'navigating the site' ! Most sites have their own search facility.

OTOH if you don't know how to use the internet as a search tool......

Graham

Ignoramus965 wrote:

scratch that, I found something

http://www.irf.com/technical-info/appnotes/an-978.pdf


That's a very good app note indeed.

For your application you should perhaps be thinking about a high side auxiliary supply. Prolly a 555 would
do the job.

Graham

On Fri, 09 Sep 2005 04:39:29 GMT, Ignoramus965
wrote:


I am hoping that I can get some help from learned and esteemed experts
here... Doubtless, I could not undertake this project alone. I hope
that there will be people who may take enough interest to stop me if I
do something stupid. I am not really afraid of, say, losing $80 that I
would spend on components that blow up, although I would prefer not to
endanger anyone's safety.

I already did many interesting things by "standing on the shoulders of
giants", such as repair of a diesel generator or building of a phase
converter etc. I am saying this not to brag -- these were relatively
simple things compared to electronic design issues that some of you
are experts in -- but rather to underscore that projects can be brought
to successful completion with a bit of care, open mind and good advice.

A bit of care, an open mind and good advice won't suffice here,
particularly if you selectively ignore the advice. Those who do
things like this successfully have had to study, why do you think that
you can skip it? Vastly superior intellect perhaps?

Some of your questions have been answered more than once, with
consistent advice that perhaps you think you can regard as "optional".
It is, of course, optional, but the results are predictable -- and
have been predicted consistently if with varying degrees of color
and emphasis.

The topic of switching high currents with solid-state devices is far
too complex to cover with answers to a few specific questions. I
think it is presumptuous of you to expect many folks to spend time
responding to isolated questions in preference to your doing the same
homework they/we had to do in order to be able to answer your
questions -- not homework specific to your questions, but to
learn the technology. There are textbooks. There is a wealth of
application notes from various semiconductor fmrs. There are
courses and seminars.

You have been told about MOSFET drivers and high-side drivers several
times. You persist in wanting to just use a sig gen. So do it!
You have been told about inductive power sources at least twice.
You were told about MOSFETs -- so you proposed IGBT's.

This does not suggest "inquiring mind" to me; it suggests lack of
discipline and perhaps laziness, lookin' for a back door, a shortcut,
the "easy way". There is a reason engineering is called a
"discipline".

I would like to see some evidence that you have spent some of *your*
time at serious study and lab (bench) work yourself before you ask
further questions of this incredibly willing and often eager group.
I think it's fair, and a reasonable courtesy to ask. You'll need
to research your own questions a bit if you're to understand the
answers -- and the (many) other relevant questions you probably don't
yet know you should have.

Anticipating a possible 30-second response of "Thank you, and what
might those questions be?", I can only say the myriad of questions
those skilled in the art have forgotten they once had while staring at
a charred spot where a transistor used to be. (BTW, the T in MOSFET
stands for transistor....) "Those skilled in the art" means we
dumb**** drones that did the homework and learned the technology.
You don't have to do all of it, but you do have to do some. It's a
tiny subset of electrical engineering. Nearly all who work with power
elex are mostly or entirely self-taught in that specific field, using
the same resources I've recommended to you.

Questions that might be more productive for you, when you're ready to
ask them, might more like "here's what I did, here's what happened,
what did I do wrong?", followed by "OK, I did what you suggested (if
you really did), here's what happened ......" and so on.

If your objective is simply to have a welder, then I'd strongly
suggest you find a good bargain and buy it. You do seem to be
skilled at finding bargains. The engineers at Lincoln and Miller
are not idiots. If a squarewave addon box could be done for a buck,
they'd be doing it for a buck and selling it for two. They've spent
most of two decades learning to apply power electronics to welding.

Then, of course, you'll want to learn to weld......

Ignoramus965 writes:

On Thu, 08 Sep 2005 20:41:09 -0700, Don Lancaster wrote:
Pooh Bear wrote:
Ignoramus965 wrote:



There's quite a bit of gate capacitance in larger MOSFETS that has to be
quickly filled or emptied. Drivers are by no means trivial.

Don, what are your thoughts on using IGBT's for switching?


Ig, I think you would be better served by getting a pile of little
transistors, a couple 9v batteries and working on your H bridge design
until you can get it generating AC sufficient to light 2 leds in
parallel with polarities opposed. Once you have AC, then start
increasing power.

Worrying about selection of hi power output drivers at this point isn't
getting you any closer to making H bridges. What people are trying to
tell you is H bridges are difficult to make, particularly for high
power. If you're trying to make a welder, then you are in for a very
difficult job. Bridges look great on paper, but once start trying to
move kilowatts around with them things get lots more complicate.

Gregm

On Fri, 09 Sep 2005 05:56:24 +0100, the renowned Pooh Bear
wrote:


Trouble is....

Even when you do know it, you're likely to fry several by accident for good measure anyway !

Fzzztttzzzzzzttt ! poPPPP ! BANG !!

Graham ;-)

Yup. ;-)


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Ignoramus965 wrote:
My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

i

No. You need a different signal for the high side drivers referenced
to the midpoint of the bridge. Wasn't this question answered already
in an earlier thread? Also, large power stages require a lot of
current to drive them. In basic EE classes, they teach you the gate
driver problem (how can a circuit with no dissipative elements still
dissipate power). You need to understand this problem before designing
gate drivers. I believe Don Lancaster has a nice article on this
matter somewhere on his web site.

Why don't you reference a working design and ask questions based on
that? This will give a reality check and stop you from wasting
people's time and generating all kinds of noise?

I have spent some time checking the following reference design out. I
am fairly sure it will work:

http://www3.telus.net/public/a5a26316/TIG_Welder.html

Sure, you can argue all day about using a signal generator or using
MOSFET's instead of IGBT's, but why don't you reference some questions
to this design. Also, you might be able to get some advice at
www.diywelder.com. There are other designs there as well.

Good luck.

Many thanks to you, Don Lancaster, for all your teachin's over the years.
Bet your sweet bippy I've bookmarked your site!

Bob Swinney
"Don Lancaster" wrote in message
...
Pooh Bear wrote:
Ignoramus965 wrote:


My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?


Not directly.

You'll need some level translation.

If you don't know what that means then you shouldn't be attempting to
make a
welder.

Unless you fancy welding *yourself* to something ? Terminally maybe ?

Btw - electronics hobbyists are advised to try out *low current* stuff
before progressing to the 'arcs and sparks' scenario !

Graham


There's quite a bit of gate capacitance in larger MOSFETS that has to be
quickly filled or emptied. Drivers are by no means trivial.

In fact, the design of the driver stage is usually much more difficult
than the output stage.


--
Many thanks,

Don Lancaster
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
voice: (928)428-4073 email:

Please visit my GURU's LAIR web site at http://www.tinaja.com

Just curious. You want to build something that can be difficult for
experienced engineers, for instance the fellow working on the bench
opposite mine last week. What electronic test equipment do you have?

jw

Graham sez:

" trouble is.... you really have to have been doing this stuff for ages to
pick up
the relevant issues. For a beginner, jumping in at the deep end involves a
cliff-like learning curve."

Your best reply so far! Hopefully, Iggy will be wise enough to heed some of
your (and other's) advice and pull back his ambition enough to realize there
are no instant answers to success in the electronics game.

Bob Swinney





"Pooh Bear" wrote in message
...

Ignoramus965 wrote:

Don, what are your thoughts on using IGBT's for switching?

Graham replies that they're very good these days.

Mosfets are best at the higher frequencies though.

IGBTs have their own little 'quirks'.


Graham

You'll need a high-frequency Tek current probe and a shunt to debug
power circuits. A big Variac and some load resistors are very helpful.

jw

I've been following these threads and I must say I find it kinda scary.
I've been "doing" electronics since I was about 12 and I'm now 70.
I've done radios, audio, logic, switching power supplies and other
things. Of these, I have found the switching power supplies the most
difficult to get right. I built my first one in 1960. The higher the
power, the more difficult dealing with a myriad of tricky details.

In spite of all that experience, my welder is a Thermal Dynamics (now
Thermal Arc) 250 GTSW. I never even considered building my own. For
one thing, I'll lay better than even odds it would cost me more.

If you want to get into switching, try a class D audio amp. Then go on
to something like a variable voltage, current limited + and - 0 to 50
volt 10amp bench power supply.

Then think about whether you want to do a welder.

This is not intended to put you down or discourage you, rather to try to
set you on a path where you can expect reasonable success.

Ted

Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

thanks

i

I would not use the signal generator because it isn't really optimal for the
job, and if you get for example a drain to gate short in a blown MOSFET,
you will quite likely destroy your Wavetek. Get the National Semiconductor
datasheet for a 555 timer and build yourself an oscillator. This is
seriously just as good for what you are doing, and when it blows up you
will be less upset (or at least I would). If you need to drive MOSFET
gates fast, I recommend TC4421 or TC4422 chips connected after the 555,
they are supposed to put out 9 Amps, which your Wavetek can't do. The 555
can run off a 5V regulator. Keep the wires from the TC4421 to the MOSFET
shorter than 1 inch for low inductance, and put ceramic and electrolytic
decoupling caps right next to each 4421.
Chris

Well said Don. I was thinking along the same lines, only to find you'd
said it better already.

Steve

Don Foreman wrote:

On Fri, 09 Sep 2005 04:39:29 GMT, Ignoramus965
wrote:




I am hoping that I can get some help from learned and esteemed experts
here... Doubtless, I could not undertake this project alone. I hope
that there will be people who may take enough interest to stop me if I
do something stupid. I am not really afraid of, say, losing $80 that I
would spend on components that blow up, although I would prefer not to
endanger anyone's safety.

I already did many interesting things by "standing on the shoulders of
giants", such as repair of a diesel generator or building of a phase
converter etc. I am saying this not to brag -- these were relatively
simple things compared to electronic design issues that some of you
are experts in -- but rather to underscore that projects can be brought
to successful completion with a bit of care, open mind and good advice.



A bit of care, an open mind and good advice won't suffice here,
particularly if you selectively ignore the advice. Those who do
things like this successfully have had to study, why do you think that
you can skip it? Vastly superior intellect perhaps?

Some of your questions have been answered more than once, with
consistent advice that perhaps you think you can regard as "optional".
It is, of course, optional, but the results are predictable -- and
have been predicted consistently if with varying degrees of color
and emphasis.

The topic of switching high currents with solid-state devices is far
too complex to cover with answers to a few specific questions. I
think it is presumptuous of you to expect many folks to spend time
responding to isolated questions in preference to your doing the same
homework they/we had to do in order to be able to answer your
questions -- not homework specific to your questions, but to
learn the technology. There are textbooks. There is a wealth of
application notes from various semiconductor fmrs. There are
courses and seminars.

You have been told about MOSFET drivers and high-side drivers several
times. You persist in wanting to just use a sig gen. So do it!
You have been told about inductive power sources at least twice.
You were told about MOSFETs -- so you proposed IGBT's.

This does not suggest "inquiring mind" to me; it suggests lack of
discipline and perhaps laziness, lookin' for a back door, a shortcut,
the "easy way". There is a reason engineering is called a
"discipline".

I would like to see some evidence that you have spent some of *your*
time at serious study and lab (bench) work yourself before you ask
further questions of this incredibly willing and often eager group.
I think it's fair, and a reasonable courtesy to ask. You'll need
to research your own questions a bit if you're to understand the
answers -- and the (many) other relevant questions you probably don't
yet know you should have.

Anticipating a possible 30-second response of "Thank you, and what
might those questions be?", I can only say the myriad of questions
those skilled in the art have forgotten they once had while staring at
a charred spot where a transistor used to be. (BTW, the T in MOSFET
stands for transistor....) "Those skilled in the art" means we
dumb**** drones that did the homework and learned the technology.
You don't have to do all of it, but you do have to do some. It's a
tiny subset of electrical engineering. Nearly all who work with power
elex are mostly or entirely self-taught in that specific field, using
the same resources I've recommended to you.

Questions that might be more productive for you, when you're ready to
ask them, might more like "here's what I did, here's what happened,
what did I do wrong?", followed by "OK, I did what you suggested (if
you really did), here's what happened ......" and so on.

If your objective is simply to have a welder, then I'd strongly
suggest you find a good bargain and buy it. You do seem to be
skilled at finding bargains. The engineers at Lincoln and Miller
are not idiots. If a squarewave addon box could be done for a buck,
they'd be doing it for a buck and selling it for two. They've spent
most of two decades learning to apply power electronics to welding.

Then, of course, you'll want to learn to weld......

Chris Jones wrote:
Ignoramus965 wrote:


My objective is to make a square wave inverter for high amperage DC
for TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the
H bridge?

thanks

i


I would not use the signal generator because it isn't really optimal for the
job, and if you get for example a drain to gate short in a blown MOSFET,
you will quite likely destroy your Wavetek. Get the National Semiconductor
datasheet for a 555 timer and build yourself an oscillator. This is
seriously just as good for what you are doing, and when it blows up you
will be less upset (or at least I would). If you need to drive MOSFET
gates fast, I recommend TC4421 or TC4422 chips connected after the 555,
they are supposed to put out 9 Amps, which your Wavetek can't do. The 555
can run off a 5V regulator. Keep the wires from the TC4421 to the MOSFET
shorter than 1 inch for low inductance, and put ceramic and electrolytic
decoupling caps right next to each 4421.
Chris


Triple 5's work great but you might want to look into an astable
multivibrator with a tuning capacitor as you can build one up to handle
voltages you can't imagine. Then if you hookup a pocket O'scope ($160
allelectronics.com), or build a simple freq counter($30 parts find free
scats online). Then you can monitor your output frequency. And as an
alternative to mosfets try a power triac(2 Z diodes chained together) or
a variac might work but cost prohibitive if they smoke up, I usually
just use them as clean-low power power supplies. What Chris recommended
will work I just wanted to give you a different perspective and some
other options.

X

On Sat, 10 Sep 2005 01:00:20 GMT, Ignoramus965
wrote:



What I am not sure about is what kind of signal is sent to inputs of
the IR 2110 chip. I have its application notes printed out, but have
not yet read it.

i

Anyone who could answer this question has read the specsheet. Why
can't you?

On Sat, 10 Sep 2005 03:48:40 GMT, Ignoramus965
wrote:

On Fri, 09 Sep 2005 22:46:02 -0500, Don Foreman wrote:
On Sat, 10 Sep 2005 01:00:20 GMT, Ignoramus965
wrote:



What I am not sure about is what kind of signal is sent to inputs of
the IR 2110 chip. I have its application notes printed out, but have
not yet read it.

i

Anyone who could answer this question has read the specsheet. Why
can't you?


I have it on paper, in front of me. There are specifications of levels
and such, but not a description of what it does. I will check it some
more.

Having it in front of you doesn't help unless you read it, which
admittedly takes time than it does to post another question.
There are sections in the datasheet entitled:

"Description"
"Typical Connection"
"Functional block diagram"

On Sat, 10 Sep 2005 03:48:40 GMT, Ignoramus965
wrote:

On Fri, 09 Sep 2005 22:46:02 -0500, Don Foreman wrote:
On Sat, 10 Sep 2005 01:00:20 GMT, Ignoramus965
wrote:



What I am not sure about is what kind of signal is sent to inputs of
the IR 2110 chip. I have its application notes printed out, but have
not yet read it.

i

Anyone who could answer this question has read the specsheet. Why
can't you?


I have it on paper, in front of me. There are specifications of levels
and such, but not a description of what it does. I will check it some
more.

i

This has to be a troll. Congratulations, i, ya got me and us for a
while.

"Don Foreman" wrote in message
...
On Sat, 10 Sep 2005 03:48:40 GMT, Ignoramus965
wrote:

On Fri, 09 Sep 2005 22:46:02 -0500, Don Foreman
wrote:
On Sat, 10 Sep 2005 01:00:20 GMT, Ignoramus965
wrote:



What I am not sure about is what kind of signal is sent to inputs of
the IR 2110 chip. I have its application notes printed out, but have
not yet read it.

i

Anyone who could answer this question has read the specsheet. Why
can't you?


I have it on paper, in front of me. There are specifications of levels
and such, but not a description of what it does. I will check it some
more.

i

This has to be a troll. Congratulations, i, ya got me and us for a
while.


No troll, just the new head of FEMA !!!!

Best Regards
Tom.

On Fri, 09 Sep 2005 03:08:52 +0000, Ignoramus965 wrote:

My objective is to make a square wave inverter for high amperage DC for
TIG welding, from a 300A CC DC welding power supply.

I would actually be content with 200A current. AC would be used for
aluminum only.

I own a Wavetek 171 signal generator:

http://www.labx.com/v2/spiderdealer2...m?LVid=2779965

It can do up to 10 volts, supposedly, and any frequency.

Can I simply use it to drive either MOSFETs or IGBT's that make up the H
bridge?

I would disrecommend an H-bridge - the workpiece has to be grounded
to ground, or you run a risk of serious injury.

I'd be very surprised if you could design and build a circuit that would
turn your DC welder into an AC one, for less money than you can just go
buy an AC welder.

Good Luck!
Rich

Pooh Bear wrote:


Spehro Pefhany wrote:

On Fri, 09 Sep 2005 05:07:38 +0100, the renowned Pooh Bear
wrote:

Google IR2011.

That'll explain driving H bridges a bit. Be especially aware of the term
'high side drive'.

Graham

Better read the application notes really carefully too. What you don't
know will fry expensive semiconductors, typically a few at a time.

Best regards,
Spehro Pefhany

Trouble is....

Even when you do know it, you're likely to fry several by accident for
good measure anyway !

Fzzztttzzzzzzttt ! poPPPP ! BANG !!

Graham ;-)

I testify to that. I have even managed to make a plastic to-92 package
explode. Driven a power FET into thermal runaway and destroy it. and fried
more IC's with electrostatic damage than i could count.
--
JosephKK

Ignoramus965 wrote:

On 09 Sep 2005 07:48:05 -0400, Greg Menke
wrote:
Ignoramus965 writes:

On Thu, 08 Sep 2005 20:41:09 -0700, Don Lancaster
wrote:
Pooh Bear wrote:
Ignoramus965 wrote:



There's quite a bit of gate capacitance in larger MOSFETS that has to
be quickly filled or emptied. Drivers are by no means trivial.

Don, what are your thoughts on using IGBT's for switching?


Ig, I think you would be better served by getting a pile of little
transistors, a couple 9v batteries and working on your H bridge design
until you can get it generating AC sufficient to light 2 leds in
parallel with polarities opposed. Once you have AC, then start
increasing power.

Worrying about selection of hi power output drivers at this point isn't
getting you any closer to making H bridges. What people are trying to
tell you is H bridges are difficult to make, particularly for high
power. If you're trying to make a welder, then you are in for a very
difficult job. Bridges look great on paper, but once start trying to
move kilowatts around with them things get lots more complicate.

Fair enough. If I get that welder, then I will start with a smaller
scale inverter. I hope that I could reuse it for larger scale, in some
manner.

i
Actually you might try to make a micro-arc-welder before scaling the power
up much. The load properties of an arc-welder includes almost all of the
worst case load characteristics, including open circuit, short circuit,
very high harmonic contents, wildly variable load impedances, and negative
resistance slopes. protect and oversize your components zealously.
--
JosephKK