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

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term 'high side drive'.

before venturing into this

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

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

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 dumbshit 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......

Thanks Don. I will definitely start reading a lot about that stuff.

i

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

measure anyway !

Yup. ;-)

Best regards, Spehro Pefhany

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

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:

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 There are other designs there as well.

Good luck.

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

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

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

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

Thanks. I will check out his website.

That's a good idea. I will check things out.

Thanks. I spent a while reading that page, and was quite impressed.

I have not seen it yet, but I will check it out.

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

D>>

Thanks. I ordered the art of electronics and will peruse it.

I found this schematic to be actually understandable.

from

If I end up using IGBT's as that guy did, I would have one big one per each leg of the letter H.

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

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.

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