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| 30A precision current source |
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| Doctorandus_P:
I would probably build this from an audio amplifier and a resistor to measure the current, or measure the current by putting a DMM in series. You can also easily relax the current you have to drive by putting a few windings on your current transformer. I.E, if you put 5 windings on the transformer, you only have to generate 30/5 = 6A. Also think about what sort of accuracy you want. 1mA resolution in a 30A range is 1:30000, which would require a 15 bit adc. An easy solution is to make 2 or even 3 measurement ranges. |
| Zero999:
--- Quote from: ali_asadzadeh on April 07, 2019, 06:27:16 am ---Thanks all for your suggestions and hints. --- Quote ---It's clearly not a bipolar current source (it's a simple current sink). I'm guessing you implied you want a bipolar source (and several here have understood so, probably because of your 'DC bias' remark) whereas I don't see it clearly stated in your post unless I missed something. With a 0-3.3V input sine signal, you'll just get a current sink between Imin (won't be 0, there will be a significant offset) and 3.3/Rshunt basically. That could be what you wanted after all. Unclear. Also, with 5V supply for your DUT, make sure you'll have enough headroom - we don't know anything about your DUT. --- End quote --- As I mentioned the DUT is a simple wire wrapping 1 turn inside a CT. --- End 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. --- Quote --- --- Quote ---No the circuit will not generate an AC current, without a DC bias. What's the frequency range? What's the maximum output voltage, at 30A? If space isn't limited and the output voltage only needs to be 1V or so, then how about using a transformer to step-up the current, whist reducing the voltage? 1mA to 30A is a huge dynamic range. Your circuit will need multiple different range settings to give a decent level of accuracy. --- End quote --- The frequency range is from 40Hz to 400Hz, the maximum open output voltage is not important, the lower the better, because we have less dissipation. Here Came something completely different to my mind! I can buy dirt cheap 5V 40A power supplies, something like this, Also for the DAC, I decided to switch to an audio codec part, with 24Bit resolution (CS4344), This time the output is bidirectional, also I have managed to use a current sense IC instead of shunt resistor, Any Idea's about this new design? --- End 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. IF a dual power supply is an issue, the circuit I posted previously can be bridged. |
| ali_asadzadeh:
--- 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 ;) |
| gf:
--- Quote from: ali_asadzadeh on April 08, 2019, 05:37:58 am ---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 --- Note, the MOSFET you had selected has a specified ON resistance of up to 77 mOhm. At 30A this gives already a voltage drop of up to 2.3V at a single, fully condicting MOSFET (and you need to drive the gate with > 10V in order to get this state -> btw, keep in mind the required output voltage swing of the driving opamp). So with two ones in series (bridge), there are only 0.4V left for the DUT, at 5V anyway. Btw, what is on the other side of the CT? The impedance at the secondary side eventually gets transformed to the primary side, therefore the impedance which terminates your AC current source may be significantly higher than just the resistance of the wire (and may require a higher voltage then). |
| pansku:
I once did some planning for a similar project, but never got to the point of simulation. However I suggest that you could look at this paper for some inspiration: A Wide-Band Transconductance Amplifier for Current Calibrations That circuitry is good for 8A Rms and has over 100kHz of -3dB bandwidth. |
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