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Forum Index : Electronics : Replacing a BJT with an IBGT?
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SimpleSafeName Guru  Joined: 28/07/2019 Location: United StatesPosts: 319 |
Hi guys, I've got an old Yaskawa drive that had an event the other day. It looks like some of the BJT triggering wires got shorted together and put a couple of large, ancient, transistors conducting which took out the dynamic braking resistors as well as a 2SD466 and a 2SD915 transistors. The '466 transistor isn't so bad, but the '915 is $55 which got me wondering if I could use a similar IGBT as a replacement? And yeah, $70 for both BJTs isn't bad, but how many others are on "death's doorstep" after what happen (the remaining ones seem to check out okay with a DMM). The control boards seem to have survived unscathed, so this might be an easy fix. Ideally, we would like to replace the drive with something a bit more modern (the drive is from 1980). The motor that it runs is a spindle motor for a lathe with resolver feedback. The motor itself is a synchronous AC 3 phase motor. Any thoughts on a replacement for it? Thanks, John |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Bjt's are current driven devices, so will need to have continual current supplied during each switching event, however IGBTs (like mosfets) are a voltage device, so once the gate is " charged " thats it.. saying that, it completely depends on how each device is driven, sometimes they can be interchangeable but would have to know how they switched. Also ( I don't think in this case, but could be wrong) BJTs can be " biased " on ( so partially on) eg. like in a amplifier, obviously this would be devastating to the device if a IGBT or Mosfet is used as a drop in replacement as it would most likely never turn off. Maybe if you could get a schematic for the device if possible, would greatly help determining whether or not you can.. I think it works !! |
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| SimpleSafeName Guru Joined: 28/07/2019 Location: United StatesPosts: 319 |
Your point on the MOSFET staying on is well taken, and I was aware of this. But I would think that the base returning to zero volts would switch the IGBT back off. Whether the base actually returns to zero is another matter entirely... As for modulating the current from the BJT, it's a PWM drive so saturating the IGBT (or BJT in this case) is a good thing and to be expected. I did find a much better source for the BJTs, $6 each, although it's a TO-3 package instead of a stud mount package. Beggars can't be choosers. We will just have to get creative with a heatsink for it. I bought 3 of each since I can see myself messing up the only 2SN915 BJT in the western hemisphere if I got just one of them. I also managed to shave $15 - $35 off of the resistors by going with a more common 150 ohm, 100 watts (times six in parallel) instead of the harder to get 100 ohm, 150 watt (times four in parallel) configuration. We are planning to move the resistors outside of the drive box in any case so this works out perfectly. Thanks for the reply and insight. :) I'm going to go with the proper-ish BJTs and hope for the best on the control boards. If they got messed up, I'll be pretty much done for. As for a schematic, I've got the Yaskawa manual for the CPCR-QR drive. Brace yourself, I'm pretty sure that it pre-dates the Gutenberg press... :) DE6429218.pdf |
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| noneyabussiness Guru Joined: 31/07/2017 Location: AustraliaPosts: 512 |
Probably the safest to go with original, I do agree that by the looks of it there is no biasing, just switching, but what voltages are used for switching etc.. the only thing i can see ( please correct me if im wrong) is a " base driver " which could be anything... Sorry I couldn't be more help... I think it works !! |
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