Tool/software:
I want to design a current amplifier for measuring current through motors buy using shunts
the motors are DC
AC 3 phase motor
AC Pwm motors
frequency 0-300k
current 0-5A
voltage between lines can reach up too 680v AC
output of amplifier 0-+- 10v
can be also an amplifier with supply voltage of one polarity better 2 polarities
Hello Sammy,
You may want to use a difference amplifier for this application, however, if you are doing inline current sense, and the common-mode range is switching quickly, you may begin to see distortion due to the amplifier feedback loop being unable to adjust for the change in common-mode. Please see the below thread on a similar application.
Unfortunately, we do not have a higher speed difference amplifier capable of large common-mode voltage swings, and even the INA149 cannot support all the way up to 680V AC.
The INA149 is the highest voltage difference amplifier we currently have.
Building a solution for this discretely would be difficult, since you will need substantial attenuation, which requires large resistance, which will introduce a low-pass filter due to the large resistance and the small input capacitance of your device. For example, using the RES60A-Q1 and the INA848, you will see a -3dB point at 471kHz just based on the input resistance of RES60 and the input capacitance of INA848. This does not include any capacitance from the RES60. Using smaller value resistors will mean that you have less effect from the capacitance, but will now have some extra power loss through the resistor divider.
Discrete circuit with simplified RES60
Transient Simulation:
AC Simulation
Best,
Gerasimos
