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Current clamp oscillating at 50MHz
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Topic: Current clamp oscillating at 50MHz (Read 920 times)
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ocset
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Current clamp oscillating at 50MHz
«
on:
November 17, 2018, 04:04:25 pm »
We have a DALI power bus comprising a 15mA current clamp in a 15V rail. (as in attached schematic)
As a test, I turned on the transistor, Q4.
When I clipped a scope probe (or even a TA041 diff probe ) across the 82R resistor, I sometimes saw a 50MHz sinusoidal oscillation across this 82R resistor, of about 250mV pk2pk.
Sometimes I have to grab and release the ends of the probe to “start the oscillation off”.
We want to stop this oscillation. Do you agree that a good way to damp out this oscillation is to put an RC series circuit from Collector to base of Q3? ( Values of 10n, 10R)
I did this in the lab and it certainly put an end to the oscillation, though we wonder if there is a better way to stop it?
NXJ1S1215 datasheet:
https://power.murata.com/data/power/ncl/kdc_nxj1.pdf
TLV431 datasheet:
https://www.diodes.com/assets/Datasheets/TLV431.pdf
FMMT491A datasheet:
https://www.diodes.com/assets/Datasheets/FMMT491A.pdf
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Wolfgang
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Its great if it finally works !
Re: Current clamp oscillating at 50MHz
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Reply #1 on:
November 17, 2018, 09:24:33 pm »
... another way would be a resistor between the sense input of the TLV431 and the current sense resistor (say, 1K), plus a small cap between the anode of the TLV431 and the sense input (try a few 100pF).
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