Current measurement for a mosfet h-bridge

[rpicatoste]

Dear all,

I have a mosfet h-bridge feeding the phase of an electric motor.

For measuring the current we were using so far a **broken link removed** but now the ADC will be in the high power side and therefore the isolation given by this component is not an advantage anymore.

I am trying to get an accuracy of around 0.15 A for a ±15 A range. (0.5 % of full range)

Is this kind of device still a good option or a sense resistor could give better results? (or other way)

I think that probably a precision resistor (0.1% tolerance for example), plus the amplification and offset (to get a proportional shifted voltage between 0 and 5 V to be read by the ADC) could give better accuracy than the LTSR (0.7% accuracy plus 0.1% non-linearity), but probably the common mode voltage applied to the resistor could make a precise measurement difficult.

The switching frequency is 50 kHz, and the voltage supply for the bridge 170 V.

Thank you very much in advance for any advice!
Ricardo

 

[FvM]

You didn't tell, but apparently you want to measure the motor current. Usually an isolated current sensor (hall effect or shunt with isolation amplifier) is the best way to measure it.

 

[rpicatoste]

Hi FvM, thanks for your reply!

Indeed it is to measure the motor phase current.

In this case as I mention the isolation is not needed anymore since the ADC will be in the high power side and the signals transmitted and isolated digitally to the microcontroller.

And since the accuracy given for the current sensor is just over the needed one, I was considering the shunt resistor, which seems a simple solution but is not that common to use, and I would like to know if there are obvious reasons not to do so.

Ricardo