Re: General Board Current Monitoring on Scope

VA a écrit :
Hi all,

I am a power electronics engineer and work for a company that
manufacturers multphase synchronous buck converter control ICs (VRM)
for core power applications (among other things).

For an analysis that I am doing I am trying to capture on the scope
multiple phases inductor currents to see controller's current sharing
scheme. The controller uses a DCR current sense network and the IC is
voltage mode control. I use a standard Textronic 4 channel
oscilloscope (TDS 3032).

http://www.valuetronics.com/Details.aspx?ProdID=4238&Model=Tektronix_TDS3032
I have tried the following ways

1. Using a current probe and a current loop near the inductor. I want
to avoid such a measurement since the loop adds inductances to my
current path and will interfere with DCR time constants and my current
sense network

2. Using a differential probe and measure the voltage across across
the Capacitor (Cb) of the DCR sensing network. The signal levels are
in the order of 30-50mV at full load. The offsets in the probe cause
erroneous readings. If there is a good differential probes that any of
you recommend, it would be helpful.

3. Floating Ground measurements: Float the scopes ground and measure
the differentia voltage across Cb by removing the ground connections
on a standard scope probe. One end of Cb is close to Vout and hence is
a quiet point which I can use as a reference. This measurement
technique gives me accurate results but I cannot observe more than one
phase current at a time as there is a circulating current path through
the VRM and the scope that messes up my scope capture.

If anybody has used any circuit, instrument or have ideas which you
think can help me....do let me know. Looking for ideas....thanks in
advance

With this...I complete my third part of my triology of some of my
interesting problems....great to find a discussion forum like this.
VA
ps:


If the needed voltage compliance isn't too high (under 10V) then there's a superb diff probe amplifier for you : AD8129-8130. And it'll provide way more BW than you'll ever dream.
A small PCB will the usual surrounding protection stuff for all the channels you need and voilà.


--
Thanks,
Fred.
.

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