Dear All,
I plan to prepare a current probe.
I want to see the waveform of a switching current on a PCB.
The frequency of the switching current is 300 kHz and the peak to peak current is 50 A.
I know a usual resistor is not suitable for it. Rogowski coil is very hard to implement. coaxial shunt also is difficult!
How can I solve the problem?
Regards,
Ras
dear researcher
please check this attachment and refer to it.
Regards
https://www.transphormusa.com/sites/default/files/public/AN0003-Layout%20and%20probe%20R%202.0.0_0.pdf
Hello, slightly depends on whether you only want to make interim measurements or require a permanent solution... And - naturally - on costs.
1 milliOhm resistors are available for such tasks - regarding permanent solutions.
As well there are current transducers (check e.g. for "LEM" - a swiss company).
If you only want to assess waveforms in AC, you could resort to your "homemade" current transformer: interrupt the PCB trace, solder a wire to the stubs and thread it through HF ferrite toroid. Now you can thread some turns of a second wire through the toroid and terminate them with a resistor (higher resistance preferred). Measuring the voltage over the resistor gives you an AC assessment of the primary current. (This setup is nothing else than a transformer, so transformer rules apply.)
An afterthought: when using a current transducer, check for max. current, max. frequency AND "DC capabilities". This will ease your life. (AC transducers are ok if you have the experience to interpret the results. DC transducers are more like "showing the bitter truth" and require less of interpretation.)
Wish you success - - - and have fun!
I think a usual resistor has some inductive effect and it is not suitable for switching currents; so there is coaxial shunts
But I wouldn't like to break traces on the pcb during research phase. So hall effect/fluxgate/rogowski concepts are suitable for this.
I tried a toroidal coil with a few turns and get a good result. It is simply possible to detection transients, determine duty cycles and ...
To obtain original waveform We can integrate the output of the coil. An important point is to use a high frequency core material.
But there is some question:
- What is the difference between current transformer and rogowski coil wounded on a magnetic core?
- Is it possible to use such a rogwski coil in open secondary? ( in current transformer it isn't possible )
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