Electronics > Projects, Designs, and Technical Stuff
Expected quite some noise, but found nearly none.
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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