Importance
of the floating bus voltage for current sensing
This is used in high voltage
>100V, high side current sensing applications
For some application 400V common the mode is prepared but ic available on market will support only somewhere around
100V, but the circuit can be modified slightly to support them to 400V, its
called a floating supply voltage to the current sensor where the current sensor
is not referred to GND but supply rails are between supported voltage, this is
done but using Zenor diode which will float supply rail of the current sensor
between 400V and 395V if 5V Zenor is used.
The following reference is from Texas instruments
Rail-to-rail opamp OPA333 used to mirror the sense voltage across the shunt resistor on a precision resistor R1.
OPA333 is mirroring the sense of the voltage across Rshunt to the R2
The opa333 is floated up to 400V by
Zener diode, so the OPA333 is not referred to as the GND, it sits somewhere
between 395V to 400V so supply rail difference is 5.1V, also inputs are not
referred to the GND in this circuit.
The 600V P-Fet is used to perform
the current following where the gate is controlled by OPA333, the P-Fetis never
fully turned on, gate voltage will be adjusted by opa333 precisely to mirror
the Vshunt across R2.
The voltage across R1 sets the drain a current of the FET and by matching the resistor R2 in the drain of the FET to
be equal to R1, VSENSE voltage is developed across R2 (VR2).
Additional INA226 is not also on
400V, so it does not need higher common-mode voltage, voltage divider has used
to drop 400V to INA226,
INA226 measure only 100mV across the
R2
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