Electronics > Projects, Designs, and Technical Stuff

Expected quite some noise, but found nearly none.

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eTobey:
Hi,

i have a coil, that i send current through with a half bridge. After the coil i have a shunt resistor, and there i measure the current (green trace in ampere), that swings (seemingly) about 2.6A pk-pk with quite a steep slope. It is the second ringing on the screenshots, that i refer to.

Blue trace:    Gate of HS
Red trace:     Voltage of shunt (0.104Ohm)
Yellow trace:  Measured noise with a 15mm shorted loop.
Green trace:  Ampereof coil

Full bandwith with peakdetect.

The loop was help right on the cable, but there was only 20mVpk noise. I would have expected about 10 times more. Other chips on the PCB generate higher peak noise.

Do i measure a signal that is not there with that amplidtude, or do i have to measure this noise differently?


temperance:
The induced voltage depends on the rate of change of current.

eTobey:

--- Quote from: temperance on January 11, 2025, 11:55:21 pm ---The induced voltage depends on the rate of change of current.

--- End quote ---
227A/us would not be quite a rate of change?

jonpaul:
Ringing due to poor probe technique and bad breadboard setup.


Read about power supply measurements and probe measurements first.

j

mtwieg:
Your descriptions of the scope traces don't make much sense:


--- Quote ---Blue trace:    Gate of HS
--- End quote ---
I'm guessing we see two transitions because of dead time in the half bridge? Is the y scaling right, drive voltage is only around 5V?

--- Quote ---Red trace:     Voltage of shunt (0.104Ohm)
--- End quote ---
So it looks like the current shoots up to >30A (3V/0.1ohm), at which point the trace is off the screen... is that right?

--- Quote ---Yellow trace:  Measured noise with a 15mm shorted loop.
--- End quote ---
.... what?

--- Quote ---Green trace:  Ampereof coil
--- End quote ---
So you're measuring current with something else besides the shunt resistor (red trace)? What's the sensitivity of this sensor?

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