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30A precision current source

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ali_asadzadeh:
Hi,
I want to generate from 1mA to 30A 50Hz sin wave currents for a system, it’s main use is to test and calibrate the DUT internal CT’s and current measurements circuits.

Here is a suggested circuit, That I have in my mind, I would generate a sin wave with a 16bit dac 0 – 3.3 V connected to my MCU, the output of the DAC would go to the positive input of the op-amp.

For simplicity I have only drawn 2 MOSFETs , But I plan to use 5 to 10 parallel MOSFETs, I want to use a PC power supply as the DC source of this circuit, I will use the 5V output for the current source, is this circuit Idea practical? And does this circuit generate a sin wave without DC bias?

Also, I thought Maybe I should change the 10mOhm sense resistor with a current sense IC like ACS712 from allegro, But the problem with them is that their zero current value is mid supply which is 2.5V, any Idea on how to use them, they would make it much simpler.

For the DAC Part I plan to use DAC8411IDCKR from TI,
Any Ideas?


gf:

--- Quote from: ali_asadzadeh on April 06, 2019, 06:29:40 am ---And does this circuit generate a sin wave without DC bias?
--- End quote ---

No, it is a (unidirectional) current sink, which draws current from DUT's pin 2.
But would you really want to feed a positive current into DUT's pin 2?
The latter would imply that the voltage at the DUT's pin 2 would need to be raised to > 5V, and the 5V voltage source would need to be capable to sink the current (I doubt that a PC power supply can sink significant amounts of current).

ali_asadzadeh:

--- Quote ---No, it is a (unidirectional) current sink, which draws current from DUT's pin 2.
But would you really want to feed a positive current into DUT's pin 2?
The latter would imply that the voltage at the DUT's pin 2 would need to be raised to > 5V, and the 5V voltage source would need to be capable to sink the current (I doubt that a PC power supply can sink significant amounts of current).
--- End quote ---

Thanks for the feedback, the DUT is just a simple short wire, it would goes across the center of CT,So does this solve the sink current to the PC power supply?

what's your Idea about the circuit? how should I change it?

Zero999:
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.

soldar:
You could use an old arc welding machine which is just a stray field transformer (a transformer with a magnetic bypass or shunt in its core) which limits max current. Set it to 30 Amps or less although for very low currents you will probably need to use a resistor.

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