APPLICATION INFORMATION

FUNCTIONAL PRINCIPLE OF CLOSED-LOOP CURRENT SENSORS WITH MAGNETIC PROBE

Integrator

Filter

Probe

Interface

H−Bridge

Driver

V

OUT

REF

IN

I

COMP2

R

S

I

COMP1

Compensation

Diff

Amp

Timing, Error Detection,

and Power Control

Degauss

V

REF

V

REF

GND

+5V

IS1

IS2

DRV401

I

P

Compensation Winding

Magnetic Core

Primary Winding

Field Probe

FUNCTIONAL DESCRIPTION

DRV401-EP

USING THE DRV401

Closed-loop current sensors measure current over wide frequency ranges, including dc. These types of devices

offer a contact-free method as well as excellent galvanic isolation performance combined with high resolution,

accuracy, and reliability.

At dc and in low-frequency ranges, the magnetic field induced from the current in the primary winding is

compensated by a current flowing through a compensation winding. A magnetic field probe, located in the

magnetic core loop, detects the magnetic flux. This probe delivers the signal to the amplifier that drives the

current through the compensation coil, bringing the magnetic flux back to zero. This compensation current is

proportional to the primary current, relative to the winding ratio.

In higher frequency ranges, the compensation winding acts as the secondary winding in the current transformer,

while the H-bridge compensation driver is rolled off and provides low output impedance.

A difference amplifier senses the voltage across a small shunt resistor that is connected to the compensation

loop. This difference amplifier generates the output voltage that is referenced to REFIN and is proportional to the

primary current. Figure 1 shows the DRV401 used as a compensation current sensor.

Figure 1. Principle of Compensation Current Sensor With the DRV401

The DRV401 operates from a single +5 V supply. It is a complete sensor signal conditioning circuit that directly

connects to the current sensor, providing all necessary functions for the sensor operation. The DRV401 provides

magnetic field probe excitation, signal conditioning, and compensation coil driver amplification. In addition, it

detects error conditions and handles overload situations. A precise differential amplifier allows translation of the

compensation current into an output voltage using a small shunt resistor. A buffered voltage reference can be

used for comparator, analog-to-digital converter (ADC), or bipolar zero reference voltages.

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): DRV401-EP