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AMC1200EVM: High voltage current measurement

Ismail Hussain
Prodigy 40 points
Part Number: AMC1200EVM
Other Parts Discussed in Thread: AMC1200, TIPD104

Hi, I want to measure a current from a high voltage isolated power supply (3000 volts, with ground is different (isolated) from circuit ground), The current measurement ranges from 1 microamps to 1000 microamps with a resolution of 1 microamps. I would like to measure the current either from low side or by measuring the differential voltage across a shunt resistor (1k ohm). Please let me know if i can use AMC1200EVM board to measure current or differential voltage (1 milivolts to 1 volts ). If not, please let me know the solution for measuring the current from isolated high voltage supply.  

Regards.

Ismail

  • 0
    TI__Guru**** 168485 points
    Hi Ismail,

    Welcome to our e2e forum! Can you share the schematic you intend to use with the AMC1200? The input voltage range to the AMC1200 is only +/-250mV, so your 1k shunt sounds a little high. Is the 3000V supply AC or DC?
  • 0 in reply to Tom Hendrick
    Prodigy 40 points

    Dear Tom,

    Thanks for your prompt reply, I do not have the exact schematic of AMC1200 for my circuit. Instead I have attached another schematic in which i need to replace ACPL-c87 with AMC 1200. Can I use a 100 ohm shunt resistor, so that the voltage across the resistor will be 0.1mV to 100 mV.  How can I find the resolution of AMC1200.

  • 0 in reply to Ismail Hussain
    TI__Guru**** 168485 points
    Hi Ismail,

    The ACPL device has a 0-2V input range with a gain of 1, while the AMC1200 has a +/- .250V input range with a gain of 8. If you want to measure 1A at 100mV, you would need to use a 0.1 ohm shunt. Are you trying to measure current or voltage?
  • 0 in reply to Tom Hendrick
    Prodigy 40 points

    Dear Tom,

    My ultimate aim is to measure current for the high voltage power supply.

    I am looking for the solution similar to this one. (Isolated Current Sensing Reference Design Solution, 5A, 2kV) The difference is my current ranges from (1 micro amp to 1 milli amp). Towards this requirement, if I calculate the value of shunt resistance Rsh(max) = 250 mV / 1 mA = 250 ohm. So that I will get Vout = 2V.  However when my minimum current is 1 microamps. The shunt resistance voltage is 250 micro Volts, and the Vout = 8*250 micro volts = 2 milli volts. 

    My question is: can I able to observe the value of 2 mili volts at the output?

    Or Can I go for option 2:

    Current in the range of 1 micro amps to 200 micro amps:

    Rsh(max) = (250mV / 200 microamps) = 1.25 k ohm

    minimum Vin= 1.25 k ohm * 1 microamps = 1.25 mili volts.

    minimum Vout = 8 * Vin =  8 * 1.25 milli Volts = 10 milli Volts.

    www.ti.com/.../slau521.pdf

  • 0 in reply to Ismail Hussain
    Expert 2580 points

    Hi Ismail,

    probably a logarithmic amplifier will do a good Job here ..

    With best regards

    Gerhard

  • 0 in reply to Tom Hendrick
    Prodigy 40 points
    Dear Tom,

    Any suggestion for current measurement. Please Look my reply for your previous suggestion.
  • 0 in reply to Ismail Hussain
    TI__Guru**** 168485 points
    Hi Ismail,

    My appologies - I mis-read your initial post. You wrote micro amps but I read milli amps. As Gerhard suggested, you need some gain. The shunt resistor used with the AMC1200 would ideally be sub-ohms. Large shunts will cause offset and gain errors. You could consider putting an amplifier ahead of the AMC1200 to boost (or attenuate) your signal into the full scale input range. Take a look at TIPD104.