Datasheet

"#$%
SBVS070B − JUNE 2006 − REVISED MAY 2009
www.ti.com
12
APPLICATIONS INFORMATION
FUNCTIONAL PRINCIPLE OF CLOSED-LOOP
CURRENT SENSORS WITH MAGNETIC
PROBE 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 REF
IN
and is proportional to the primary
current. Figure 1 shows the DRV401 used as a
compensation current sensor.
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
Figure 1. Principle of Compensation Current Sensor with the DRV401