Solution Finder


Posted by: underthebridge on Wed, 03/21/2012

I'm designing a LED system using LNK458, and I find it's hard to observe some signal.
For instance, I want to see the voltage of R3 in the following picture. But the system may blow when I add the probe on my board.
Is it a must to use isolated probe?


Submitted by PI-Jono on Thu, 03/22/2012

For topologies such as buck or buck-boost and once the source pin has no definite ground then you need to use differential probe.

In case you do not have a differential probe, you can use the math function of your oscilloscope. Example across R3, one probe (ch1) on the cathode of D2 to bulk ground and one probe(ch2) to the source pin to bulk ground. Then, set the math function of the scope by subtracting ch1 to ch2 to get the waveform across R3.