[SOLVED] Current transformer design and debugging

[renga92]

Hi. I thought of fixing the current sensing circuit separately and then add to this SMPS power supply circuit design. Can some one suggest me how to give the excitation source for CT (high frequency (50kHz) current)? I have normally used signal generators which generate different voltage signals. Will adding a load across the signal generator output and measure the current in the process, be used as an excitation source ? If not please suggest some method for me to excite the CT. Thanks a lot for your support then now and for what is to come.

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I am planning to make a small PC board with just the CT and signal conditioning circuitry, to debug and understand how it works.

 

[c_mitra]

This is sufficiently small to be included in the main board. Anyway, the current transformer should be in the main board because it may not be layout-friendly to have a longer current return path.

Of course you will need to test the design using a signal generator - perhaps your signal generator may not be able to provide the current levels needed for testing.

 

[Easy peasy]

you can resonate the primary winding of the CT with a large low loss cap at 50kHz say, you will need the square wave out of your sig gen and buffered by a couple of emitter followers and a good power supply (15V say) with 470uF right across the xtors, you will have to vary the freq ad the cap to get a match some where in the 50k - 100k Hz region, if you have an ammeter in your psu this will show you resonance, (higher current) you should also see it on the CT secondary...

 

[renga92]

Hi. This is what I planned to do. I will give it a try. I was looking into hall effect based current sensor. Can it measure high frequency current ?

 

[c_mitra]

I was looking into hall effect based current sensor. Can it measure high frequency current ?

50kHz is not high frequency for Hall sensors. But I do not know about the downstream circuits. But remember that the sensor is sensitive to magnetic field and not current per se.

 

[renga92]

@c_mitra : Can you give me more detail on what's a downstream circuit is ?

 

[c_mitra]

@c_mitra : Can you give me more detail on what's a downstream circuit is ?

The circuits that process the signal generated by the Hall sensor. Watch out for resistor capacitor low pass filters.

 

[renga92]

Sure. I am uploading a circuit to test the both hall effect current sensor and as well high frequency current transformer.
Please comment if there is anything that I need to add or change. Another question is do we need to give a current path for the current transformer when the MOSFET is ON ?

 

[FvM]

Your test circuit is confusing in several regards.

1. It's outputting an unipolar current and prone to saturate the current transformer. Not a suitable test or calibration setup for an AC current sensor.

2. c_mitra was asking about intended signal processing for the hall sensor. The sensor can be expected to give a signal proportional to instantaneous current. It will need rectification and averaging to produce the apparently intended magnitude value.

 

[Easy peasy]

I agree with FvM its all bad...

 

[renga92]

Hi FVM. Thanks a lot. I didn't think about it. I was planning to use bench top power supply as the power source. Do you think half bridge circuit be any better for testing AC current sensor ?
I finally got what he was telling about.I am now working on signal conditioning circuit for the hall sensor.

 

[FvM]

A half bridge with output capacitor or a full bridge are surely options to generate a dc free voltage, respectively current through a series resistor.

 

[renga92]

Hi. I got the over current protection done through a hall effect sensor. Now it is working as intended. I still have a way to go with current transformer.