SNOSDI4 March 2024 TLV1872
PRODMIX
Figure 7-3 below shows a bipolar input zero cross detector circuit. The signal source is the secondary of a current or voltage transformer which outputs a bipolar (±100 mVp to ±12 Vp) AC signal that swings around 0V (GND). Since the input voltages are not AC coupled, level shifted or further attenuated, DC accurate millivolt zero cross accuracy is possible (even with distorted waveforms). This is due to the direct DC coupled input allowing below-ground bipolar detection range afforded by the split ±12V supplies and rail-to-rail input of the TLV187x. DC coupling also avoids phase shifts caused by AC coupling and non-linearities caused by diode clamping. As the output does not require any further level-shifting or attenuation, the best possible output edge is available for the processor.