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Old 10-02-2010, 11:29 AM   #411 (permalink)
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there is a trick I've used on FET's before, honestly I haven't worked with IGBT's nearly as much so I'm not sure how similar the results would be. We put a diode across the gate resistor because we wanted the turn-off to be faster than the turn-on, I think for EMI tuning or something at the time. Cool trick though, it worked.

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Old 10-02-2010, 12:08 PM   #412 (permalink)
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Hey! That's the exact trick that Fran suggested to me. I ordered some schottky diodes, 1.8Ohm, and 3.0 Ohm resistors, so that the turn on will be 3 Ohm, and the turn off will be 1.1 Ohm. Those resistances work out so that the turn on current will be about 5 amps, and the turn off will be about 5 amps too, since the miller knee or whatever it's called happens around 6v for big igbts.
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Old 10-04-2010, 03:44 AM   #413 (permalink)
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Paul, are you using a negative voltage rail on your drivers to turn the IGBT's off? Not using it could also lead to slow turn-off times, making it run hot.
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Old 10-05-2010, 09:06 PM   #414 (permalink)
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well I'm finally at a point where I can appreciate microchip more glad they have such a pdip selection. The examples compile "out of the box", no-charge. And they have some nifty features (i.e. quadrature encoders, can bus), plus 16 bit architecture (yess!) and 30mhz clock. Had some build goodness on sine-drive pmac without much fuss. got my pickitclonekit and a couple dsPIC30F4012 en route

Release build of project `AN1017.mcp' succeeded.
Language tool versions: pic30-as.exe v3.24, pic30-gcc.exe v3.24, pic30-ld.exe v3.24, pic30-ar.exe v3.24
Tue Oct 05 19:32:10 2010
----------------------------------------------------------------------
BUILD SUCCEEDED
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Old 10-05-2010, 09:18 PM   #415 (permalink)
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Heck ya! Getting everything initialized properly with the dsPICs is a little like giving birth to a very very large talk show host, but once it's done it's done. They really are very versatile chips, that are designed around every type of motor control. It really shows.

Oh! The gate resistors and diode came today, so now I get to see how that bugger behaves with on gate resistor value of 3 Ohms, and off resistor value of 1.1 Ohms. I can't wait! It's so much fun having a job so that there's no time to work on this! hurray! hahahaha. Just kidding. That's not actually fun.
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Old 10-05-2010, 09:28 PM   #416 (permalink)
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more fun than not being able to afford parts
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Old 10-05-2010, 10:25 PM   #417 (permalink)
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From experience I can say its the same amount of fun. haha
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Old 10-09-2010, 02:39 PM   #418 (permalink)
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:3 So any improvement with them new parts? XD Or just too busy?
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Old 10-09-2010, 02:43 PM   #419 (permalink)
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I just added the new gate resistors and diodes this morning. And am waiting until more time available for testing. I re-did the board to fix a couple tiny things, and I need to test an overvoltage/undervoltage circuit on a breadboard. I'm thinking of just doing a mindless top voltage hardware pwm cutout circuit so that regen doesn't get to wild with the batteries.
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Old 10-09-2010, 06:34 PM   #420 (permalink)
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Oh ya, and I am waiting a couple days for the oscilloscope for testing the new gate resistors. What? Didn't it arrive already?! Yes...

Here's the story. The oscilloscope was bought by a dear dear friend that I owe a kidney to, and then the guy on ebay didn't have it in stock (he had it posted on accident), so he asked if it was ok to send me a lower end version for a few days until the other one arrives. I said sure! It arrived a couple days later, and worked great, and just 2 days ago the new and improved one arrived at his store, so that I mailed the other one back to him, and I'm waiting PATIENTLY for the other one to get here. It'll be here in a couple days! hurray!

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