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# TIDA-00753: Amplifier Gain/burden resistor selection in CT/shunt/Closed loop hall application

Part Number: TIDA-00753

Hi,

When you design CT front end circuit, how could you select R(Burden resistor) and amplifier gain? Why 0.1R are selected? Thanks.

Regards,

Xiaobing (Eric)

• Hello Eric,

Thanks for reaching out to us. While designing current sensing using CT couple of input and system specification will help to decide CT burden and Amplifier gain.

As mentioned in design guide accuracy of CT is effected with external burden resistor as mentioned in section 4.1.
If you know required current range and system accuracy you calculate burden and required Amplifier Gain.

Regards,
Srinivasan
• Hi Srinivasan,

Tks for your feedback. Here're system specification for your comments:

Primary current range: 0 to 100A,

Input current frequency: 50 or 60 Hz,

Accuracy requirement for 10% to 120% (or 100%) of full scale primary current: 0.5% (or 1%),

CT turns ratio 1:3000, C/CT-1206 from Kemet (Datasheet for reference: www.mouser.com/.../KEM_SE0204_C_CT-1104528.pdf). So pls suggest How could select appropriate parameters for CT burden resistance and amplifier gain? Tks.

Regards,

Eric

• Hello Eric,

I assume you are looking for 10% of accuracy @ 100A.

Kindly go through CT error calculations (equivalent circuit) using internal details which needs to be obtained from CT manufacturer.

Knowing full scale voltage needed @   ADC input you can compute Amplifier gain required from burden calculations from CT equivalent circuit.

Vs=Ib*Rs (Ib is burden current and Rs is burden resistor)

The design document error budget tool will help to compute total non adjusted error to be expected @ amplifier output.

Regards,

Srinivasan