Can I use a stock SIGNAL GENERATOR to drive an H bridge?

[Pooh Bear]

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

 

[Pooh Bear]

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

 

[Greg Menke]

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

 

[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 ;-)

Yup. ;-)


Best regards,
Spehro Pefhany

 

[Ignoramus965]

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

 

[Robert Swinney]

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

 

[[email protected]]

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

 

[Robert Swinney]

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

 

[Ignoramus965]

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?

Not much, a Tek 475 oscilloscope, a nice multimeter, and also a HP
spectrum analyzer. Also wavetek 171 signal generator, hp 204D (which I
incorrectly mentioned yesterday as HP 204C), and some frequency
counters. A megohm meter also. I use that stuff mostly to test
military surplus things that I sell on eBay.

i

 

[[email protected]]

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

 

[Ted Edwards]

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

 

[Chris Jones]

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/vistaSearchDetails.cfm?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

 

[Rich Grise]

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/vistaSearchDetails.cfm?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

 

[JosephKK]

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]

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.