Driver for IGBT? (-ve off and +ve on from CMOS)

"Law of Murphy." ;-)

Cheers! Rich

(off)

the chip only sees the total supply voltage. as long as that is within the device ratings, its fine.

your job is to ensure the "0V" point - where you connect the IGBT emitter - is sufficiently stiff. in practice that means +10V and -5V supply capacitors that are a lot bigger than Cge, and a good layout.

200A is a fairly big IGBT, so the zener circuit may not be the best option. but that depends on switching frequency too. My take? its an expensive part, I'd use a pair of supplies, +12V and -5V sound good.

your IGBT could have up to 100nF of gate capacitance (I have some 600A powerex/bitsashitty parts with about 120nF Cge), so you will want at least 1uF across the zener, and tens of uF of low-ESR caps across the supply rail(s).

ware the ESR of "hobbyist" electrolytics - I have seen a 10uF 16V smt part with 27 Ohms ESR, at room temperature. Personally, I never use an electrolytic unless its got 105C stamped on it....

buy the semikron driver. its not dirt cheap, but it will work, and is fully isolated. those IGBTs wont be cheap.

and *KEEP THE INDUCTANCE LOW*

Actually the "three R's" of drive design are:

Reduce Inductance Reduce Inductance Reduce Inductance

Cheers Terry

the 21094 is specd to operate between 10 & 20Vdc so could easily provide

+/- 10V, or +15V/-5V

oh yeah, its got a piss-weak output stage, too - about 120mA source,

250mA sink. dreadful.

I've been following this thread, and I'm getting a bad feeling. Unless you really dramatically hack the welder, no matter how fast you chop the current, it isn't going to switch from DCEN to DCEP - it's just going to be chopped. To go from DCEN to DCEP, you have to reverse the whole 200 (or whatever) amps. And you have to do this FAST. I think you might be barking up a tree, so to speak, but hey, it's your welder, and your IGBTs, so you can do whatever you want, and you can't help but learn a lot one way or the other. :-)

Good Luck! Rich

That's largely a sales gimmick, it only detects a dead short.

Yeah- but look at that delay time.

Oh who cares about that cryptic little thing...

How they keep that bipolar from going into secondary breakdown is the question. There must be a diode from G-E to pull it out with the reverse current. Now things are starting to fall in place- I thought that Miller effect story was hokus-pokus.

I mean a diode from G-B....

Yes, I really like their feedback features and safety features and output power. My time is not free. If I could spend $50 instead of spending a month endlessly ordering parts and such to add another output stage to an IC, I would rather do that. Obviously, there is a limit to how much I want to spend, as well.

i

High Vce could be a result of low gate/emitter voltage. Many chips have protection against that, but it is nice to see a gate driver that protects against actual problem (high Vce) rather than one of its causes, low Vge.

High Vce leaves a little bit of time to shut down the IGBT.

Yep... that's very nice in fact...

It is, though, a half bridge driver, I think that I need two to drive a full bridge.

i

have a look at

I havent used it, its their driver selection software.

or look at

for their various drivers. they work well.

Cheers Terry

LOL :)

usually. or some dumb mechanical reason. I've seen a badly melted Schnorr washer, prised from between two 1.6mm thick 300mm x 600mm Cu bus plates which were once separated with 1mm nomex. Ten bucks says it was put there during assembly.

and a loose cap screw can arc, especially if there is vibration present. arc then boom.

the correlation between changing line staff and production failures was quite pronounced, too.

Cheers Terry

It is impossible to create in my welder, which is limited to 200A. A welding machine shorts all the time (like when an electrode sticks to the workpiece), and my machine handles it just fine.

My situation is 100% different from, say, a power supply using utility power or a big battery. My situation is a "constant current" power supply.

So, while I follow the shorting discussion with interest, it does not apply to my situation. If I cannot find these semikrons at a good price, perhaps I would need to make an output stage for a small chip, but this would not be my preference.

I am actually negotiating with someone regarding buying them. He wants too much money.

I want to clarify something. To drive a full bridge, it is my understanding that I need TWO of these semikron 23 boards.

Is that correct?

i

Yes, that's what I am planning, to reverse the whole 200 amps, using a full bridge made up of two separate IGBT bricks (each is a half bridge).

Ultimately, this inverter will become part of the welder and will be mounted inside.

I agree, worst case, I will "learn a lot" and lose some money. That welder cost me $9.99 (no kidding). That said, that's why I am looking at gate drivers, to invert the current the right way, fast etc.

i

No inductive flyback? I fear that statement, my dear Ignoramus1797, in the context of our discussion, is the embodiment of ignorance.

$50 for a Semikron 23, Bwaahahaha! Oh, wait, I got one for $39 on eBay. Nice.

--
 Thanks,
    - Win

I haven't seen the schematic for the welder in question, but Miller DC TIG welders in the pre-inverter era typically used a magnetic amplifier for AC current regulation prior to rectification, with a smoothing inductor following rectification. (The mag amp "transformer" accounts for about 300 lbs of the 400 lb welder weight in these now antiquated workhorses, which will probably still be working 50 years from now when someone finally carts it off to the scrapyard.) In the Millers I have worked on there is no output current feedback to the mag amp DC control winding, (which is varied to set operating current); with a current setting of 200 A the machine might put out about 200 A with an 18 volt arc, 250 A into a dead short and 60 V on open circuit (after the inductor current dies). Might be a set of I/V curves in the welder manual but probably nothing on response times.

my welder puts out exactly what is specified, regardless of arc resistance (if the arc does not extinguish, that is). It is a hobart cybertig.

i

So, was that you who won the last auction?

In any case... I will soon receive some very nice IR2114SS chips, that do, basically, something very similar to Semikrons. They are designed for driving large IGBTs. And the nice part is, I will get them for free as samples. If all works out well, that is. Check out their datasheet, maybe you will like what it says.

i