# How to measure current pulses in a floating resistance?

Discussion in 'The Projects Forum' started by jpborunda, Oct 31, 2014.

1. ### jpborunda Thread Starter Member

Apr 9, 2014
55
0
Hello guys. Thanks to the help of a lot of you, I've built a constant current source/sink circuit. ( See VCCS attachment). The circuit is an op amp + transistor current sink, and I'm using an H bridge stage to switch the direction of the current through the Load.

The circuit works with square pulses. They are in the range of 250-500µs(pulse width) and 20-100 Hz. Each time a pulse is delivered, the H bridge alternates polarity so that the next one flows in the opposite direction.

I would like to see the CURRENT waveform at the Rload, so that I can actually evaluate how well the circuit works. To do that, I'm using 2 oscilloscope probes, connected at each side of Rload, then, by sustracting Probe1 from Probe2, I get the voltage drop at RLoad, and since Rload is known, we can calculate the current, and "see" it in the oscilloscope.

I was wondering if there is another method applicable to my circuit to measure and see the current waveform, or is this the best way to go about this. Maybe somebody has had this problem before, I don't really think I can get my hands in a current probe, they are a little to expensive for me.

Thanks a lot for the help everyone!
Happy Halloween

EDIT: sorry about the double attachments.

File size:
135.3 KB
Views:
53
File size:
147.2 KB
Views:
48
File size:
147.2 KB
Views:
27
File size:
135.3 KB
Views:
34
2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
If you used FETs for your H-bridge, the currrent in the 10 Ohm shunt would be the same as the current in the load... With BiPolars, you are summing the base currents into the shunt.

3. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
428
general radio makes some high frequency current probes (clamp on type) that should show you the waveform. a regular power line type clampon probably would not work.

4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,849
965
unless your load has a reactive component like inductance or cspacitance then the shape and phasing of your current waveform will match the voltage wave. they do not differ much in purely resistive circuits.