STMicroelectronics STEVAL-IHT008V1 User Manual page 27

UM2027
The next equation gives the proportional coefficient between V
For example, with R
resistor values and the K parameter are determined. For high accuracy, a 1% resistor
tolerance is recommended.
on the I
values:
Zero AC line voltage detection
The TRIAC phase-control needs to be synchronized with the AC line voltage. The zero AC
line voltage crossing detection uses the AC line voltage measurement. Indeed, the zero AC
line voltage occurs when the line voltage (V
case, a comparator (U7), connected to the pin 17 of the MCU, compares the V
V voltage. As soon as V
N_IM
low level, as shown in
shows that the typical delay of the ZVS signal versus the real VAC zero is 36 µs for a 230
V 50 Hz grid voltage.
= 2 MΩ, V
U AC_RMS_Max
board schematic, the resistor bridges are defined with the following
CL
is lower than V
L_IM
Figure 18: "AC line voltage measurement
DocID029048 Rev 1
AC voltage monitoring and zero-voltage
AC
= 264 V, and V
AC_IM_Max
) and the neutral voltage (V
L
the output comparator switches to the
N_IM
synchronisation
and V .
AC_IM
= 4 V, the following
) are equal. In this
N
and
L_IM
principle". This figure
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