Both Fluke and Hantek have 20kHz clemp current probes. Both eat 9V batteries—not because they are particularly power hungy, but because it is easy to leave them on by accident. For work projects, this is no problem. I just grab another battery from the supply cabinet. But for work at home, I got tired of having to buy 9V batteries and instead made a simple circuit to take 5V USB power from my oscilloscope and convert it to 9V for my current probe.
Current probes are bidirectional and need to drive both positive and negative signals to the oscilloscope. Since they only have a single 9V battery as a power supply, they operate with a virtual ground at the midrail of the power supply. Since the battery is entirely seperate from the ground of the oscilloscope, you can connect this midrail node as ground and the scope will see a signal below midrail as a negative signal. Because of this, it is necessary to use an isolated power supply for the current probe. If a linear regulator or buck converter were used, the midrail supply would be shorted to ground and the circuit would not work as intended.
CUI has a nice series of SIP (Single In-line Package) 1.5kV DC-DC converters that take a several ranges of inputs ro generate several ranges of outputs. For this application, I selected PDSE1-S5-S9-S since it takes 5V in and generates 9V out. The actual circuit board is trivially simple—it just provides input and output filtering, a place to solder the USB cable and a place to solder the 9V connector.
CUI has a nice series of SIP (Single In-line Package) 1.5kV DC-DC converters that take a several ranges of inputs ro generate several ranges of outputs. For this application, I selected PDSE1-S5-S9-S since it takes 5V in and generates 9V out. The actual circuit board is trivially simple—it just provides input and output filtering, a place to solder the USB cable and a place to solder the 9V connector.
I cut the plastic case of my current probe.