Figure 7 shows an ac line current monitor that demonstrates both safety isolation and level shifting. Safety isolation
galvanically isolates the 110 VAC line from the low-voltage, ground-based circuits. This circuit uses resistive shunt
R1 to sense ac current. The high-voltage interface circuit is referenced to the ac neutral (white) wire in a two-wire
(non-earth grounded) single-phase ac service.
ISOlinear input-side bias voltage is line-derived and uses a 3 V linear regulator. The low-voltage output-side
circuits are biased by a ground-referenced supply. Because there is no earth ground in this system, an ac line
perturbation can potentially cause high voltage to appear on the neutral (white) wire. This elevated neutral line
common-mode voltage is rejected by the Si86xx isolator's high CMTI of 35 kV/μs minimum, 50 kV/μs typical. For
more isolated level shifting application examples, see Silicon Labs Application Note “AN598: High-Speed Level
Shifting Using Si8xxx Isolators”.
Figure 8 shows a common ground loop in the transmission path of two linear circuits (a common scenario in test
and measurement, audio and other applications that use cable interconnects). The ground loop in the top diagram
circulates between the connector grounds while parasitic inductance (Z) causes ringing that generates output
noise. The bottom circuit of Figure 8 inserts the ISOlinear circuit between the signal source and receiver, breaking
the ground loop and dramatically reducing the local ground path lengths and associated parasitic inductance.