INA199: DC current measurement on Neutral Line

Hello Mahesh, 

Thanks for the question. The INA199 (and many other INAs/CSAs) could work as long as its voltage supply (Vs-to-GND) floats with Neutral. This is because of the Absolute Maximum Input Common-Mode voltage rating of -0.1V to +26V.

The next problem is level shifting the output from LINE to Earth GND or system ground, so some ADC can record voltage measurements.

One idea is to use some isolated switching power supply to generate the Vs rail for INA199 and then use a voltage isolator for the VOUT signal. You could also do the same thing, but use a digital part and then isolate the digital bus with a digital isolator. A third option is to use a current sense amplifier (CSA) with built in isolation such as the AMC1300, AMC1301, or AMC1302.

Here is some high-voltage sensing publications you could reference.

40 V to 400 V Uni-directional Current/Voltage/Power Monitoring Reference Design

http://www.ti.com/lit/ug/tidu849/tidu849.pdf

High-voltage, high-side floating current sensing circuit using current output, current sense amplifier

http://www.ti.com/lit/an/sboa295/sboa295.pdf

–48-V Telecom Current, Voltage, and Power Sense With Isolation Reference Design

Sincerely,

Peter

Thank you Peter for quick response.

In our design, system ground and Neutral line are same. So yes, Voltage supply (Vs to GND) floats with Neutral.

Micro controller which has ADC also referencing to Neutral line.  In this case can we use INA199  or any other  INAs/CSAs ?

do we need to add additional Amplifier to increase the INA199 output voltage ?

I have partial representation of our circuit. ( Measurement point is not accurate in the picture, we plan to measure at the AC LEDs strip return side)

Hi Peter,

How about using INA28X series part which has wider common voltage spec and also gives different reference options.?  

Thanks

Mahesh

Hey Mahesh,

I don't think using the INA28x series will provide any benefit in terms of VCM range. I say this because it seems your circuit is a low-side set up where you are measuring ground current of LEDs. While understand that Neutral is where HOT current returns and that Neutral is eventually connected to Earth Ground, I am unfamiliar with connecting Neutral to the GND output of 12VDC supply (GND2). I do not know what specifications or topology are for the "Off-line P.S. 12VDC" so I am not certain that connecting N to GND2 is a good idea.

Overall as long as the Absolute Maximum input VCM range of the amplifier is not violated, then the part will operate as intended.

I would recommend starting out measuring ground currents of GND2 and GND3 while they are not connected to Neutral. I believe this is what you are saying. Anyway, it seems LEDs are actually driven by DC current and not AC so this simplifies the circuitry. Just place a shunt under the LED load and above GND3 to measure LED current. If shunt is at GND2, then you are measuring the ground current of the 12 VDC. If the 12 VDC has a transformer inside and you place shunt on Neutral, then you are measuring the primary side current of 12 VDC and this current will actually be smaller than the true LED current.

Sincerely,

Peter Iliya

Thanks Peter, I asked another related question in the forum.

We are using VIPER114LSTR part as buck converter from Line to 12V. (Buck regulator GND is connected back to Neutral)

Here is the block diagram where INA282 added for reference. We are free to move Sense Resistor position to make simpler for the Current sense amplifier.

Hi Peter,

Wondering if you got chance to review our block diagram and INA282 connection. We believe common mode voltage on this line will be below 80V (which is within the spec). Please let us know if you have any comments on this.

Thanks

Mahesh 

Hi Peter,

Yes, we plan to use as low side current sense device. Thanks for reviewing the design.

Thanks

Mahesh