| Electronics > Projects, Designs, and Technical Stuff |
| How to probe high-side Mosfet gate |
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| Romain:
What solutions are there to probe high-side N Mosfet gates in a 40-100V motor controller application? I'm trying to build a list that could be useful for beginners and more advanced engineers. 1. Normal scope + differential probe (USD150-300): https://www.eevblog.com/product/hvp70/ 2. Scope with isolated inputs (USD 10k): https://cleverscope.com/news/cs448/ Video on the CS448: |
| filssavi:
Differential probes will work in a pinch, only you Usually get massive ringing due to inductance/capacitance of the lead’s probes and the high dv/dt. The gold standard right now are optically isolated probes, in the lab we have the luck of having a tek isoVu with the new mso58 and comparing the same signal between it and the normal differential probe is night and day That scope seems nice, and 10k$ is much less than what you would pay a single isovue and scope (I think it is in the 60k region msrp however we had accademic pricing for the 1gig bandwidth). However you are trusting a niche manufacturer,and also that scope is basically a 1 trick pony, with a normal scope you can do much more... Also it is really rare to need more than 1 high side gate channel, as usually once the driver is nailed you only work on timing and for that a regular probe is enough Second caveat is that if you are not using SiC/GaN and pushing really hard when switching all this is not needed |
| Dave:
At work we're using a R&S RTH1054 for this exact purpose. Does the job quite well. Contrary to popular belief, the dv/dt in motor controller power stages are often not even that high, because they're limited to reduce the EM emissions. It's always a balance between reducing the switching losses and passing the EMC tests. |
| filssavi:
--- Quote from: Dave on June 04, 2020, 10:05:13 am ---At work we're using a R&S RTH1054 for this exact purpose. Does the job quite well. Contrary to popular belief, the dv/dt in motor controller power stages are often not even that high, because they're limited to reduce the EM emissions. It's always a balance between reducing the switching losses and passing the EMC tests. --- End quote --- In case of general industrial motor drives, which are predominantly Si IGBT based you are correct, howvever that is far from being guaranteed, With wide bandgap devices, in decent surface mount packages/modules, and a good layout with loops as tight as possible, and good bypassing on the DC link, you can push the switching times way down if you need. Usually it is done where power density is desired such as on vehicular applications(planes and electric cars). The voltage range the original poster is interested in however is still low enough where he might even get away with a 100:1 passive probe (if grounding the negative dc link is not an issue) |
| free_electron:
isolation probe. |
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