| Electronics > Projects, Designs, and Technical Stuff |
| How to probe high-side Mosfet gate |
| << < (3/3) |
| David Hess:
--- Quote from: filssavi on June 04, 2020, 07:33:05 pm ---The old two probe subtraction trick can work for general electronics, however it is not applicable to high side gate drivers since it has basically no CMRR, this means you will have huge ringing during the commutation transients. that basically render looking at the gate useless (you can see if the transistor works by looking at the output voltage or current. --- End quote --- The CMRR of the probe pair needs to be calibrated before use. The variable function on the oscilloscope corrects the DC CMRR and the probe compensation trims the AC CMRR. In the past special probe pairs were available for this application which provided very good performance. The probes in other respects operate like any high impedance probe and present a high DC resistance the source shunted by the probe tip capacitance and when properly used, will work better than the differential input of a high voltage differential probe. Ringing problems indicate misuse of the probe and apply to any probe include a high voltage differential probe. The big advantage of using common probes is the availability of a coaxial connection. But a good high voltage differential probe is much easier to use. |
| uer166:
Subscribing to the thread, I would love to see a <$1k solution to measure high-side Vgs directly over reasonable edge rates (say a 200V common mode swing over 40ns), normal Si, not GaN or SiC. |
| filssavi:
Tektronix high voltage differential probes start at 1100€ for the P5200A, it does not have too much bandwidth(50MHz) but it will do if you just want to see what the gate is doing (signal integrity leaves a bit To be desired with the long antennas they call probe leads but that is unavoidable at this price point) Keysight N2791A starts even lower at 700ish dollars, however it has an even lower bandwidth (25 MHz). I am agire you can find something cheaper from China, however I would not touch those with a 10 foot pole |
| David Hess:
I think high voltage differential probes from companies like Tektronix and Keysight are lower bandwidth because they are more realistic. At higher bandwidth, the common mode rejection is so difficult to maintain that the extra bandwidth is of questionable use. |
| Navigation |
| Message Index |
| Previous page |