Electronics > Projects, Designs, and Technical Stuff
30A precision current source
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Zero999:

--- Quote from: ali_asadzadeh on April 08, 2019, 05:37:58 am ---
--- Quote ---No that circuit will only produce magic smoke. Q3 and Q4 are connected backwards and will just short Q1 and Q2 to 0V when they conduct.
--- End quote ---
OH, I see that now, thanks.


--- Quote ---IF a dual power supply is an issue, the circuit I posted previously can be bridged.
--- End quote ---
Did you draw your circuit in LT spice? would you share the design file? also can it be done with MOSFET's? and finally if I use some DC/DC converter to lower the voltage even lower like 2.5V or 1.8V is it doable? I mean using something like LMZ31530 from TI so in that way the heat dissipation would be way lower.



--- Quote ---Is it possible to access the CT or is it inside a case?

If so, then how about just wrapping more turns through the middle?

Alternatively, get another current transformer and run it in reverse.
--- End quote ---
No it's not possible, because this device main use would be to calibrate a system that we are producing.


There comes another Idea to my Mind too, Can I use the other side of the Bridge mosfets to just conduct and make a short during each sin wave cycle, so in this way I can lower the drive voltage to something even lower, like 1V ! and the total dissipation would be 30W ;)

--- End quote ---
Yes, I drew it in LTSpice. I can't upload the design file because I don't have access to that PC at the moment.

How do you plan to calibrate this piece of test equipment? You need calibrated current meter.

Using a transformer to boost the output current is the only sane way to do this. I suggest getting another current transformer, run in reverse and measure the output current using a calibrated meter.
ali_asadzadeh:

--- Quote ---Yes, I drew it in LTSpice. I can't upload the design file because I don't have access to that PC at the moment.

How do you plan to calibrate this piece of test equipment? You need calibrated current meter.

Using a transformer to boost the output current is the only sane way to do this. I suggest getting another current transformer, run in reverse and measure the output current using a calibrated meter.
--- End quote ---

Thanks for the tips, 0.1% accuracy is good enough for me, so maybe I use a 5.5 digit or a 6.5 digit bench mulitmeter to calibrate it, although it can be done at most to 10A,

Also this device would be a 4 channel one, because it would be used for a 3 phase system including earth, and I can not use another CT because I should be able to calibrate the phases of the channels too. including another CT would add phase shift into each channel output and would complicate things a lot more, I can use better Mosfets with much lower RDs on too for my last suggestion, so I can reduce the output voltage lower to reduce the dissipation.
Zero999:
Phase shift won't a problem, if it's the same for all phases.

Using MOSFET doesn't gain you much, because anything operating in its linear mode needs to drop some voltage. You could use a class D amplifier to save power, but no doubt the high frequency noise will be a concern.

I suggest you invest in a clamp meter to calibrate this.
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