SBASAD0B March 2022 – December 2024 AMC23C10
PRODUCTION DATA
The value of the shunt resistor R5 is determined by the maximum peak input voltage of 230 VRMS × 1.1 × √2 = 360 VPK and the maximum allowed current of 150 μA. R5 is therefore calculated as 360 VPK / 150 μA = 2.4 MΩ. R5 must be divided into a minimum of five unit resistors of 480 kΩ each to limit the maximum voltage drop per resistor to the allowed 75 V. The closest value from the E96 series is 487 kΩ and, therefore, the total R5 value is 5 × 487 kΩ = 2.43 MΩ.
The two diodes D1 and D2 have a forward-bias voltage from 200 mV to 500 mV at 150-μA forward current, depending on temperature, and therefore satisfy both the minimum required voltage swing and the maximum allowed input voltage at the INP pin.
The reverse-bias capacitance of D1 and D3 of 3 pF (maximum) together with R5 form an input filter with a corner frequency of less than 22.1 kHz or a delay time of approximately 7.2 μs (maximum). The corner frequency of the low-pass filter can be adjusted down by inserting a small-value capacitor (C6). A larger filter capacitance is preferable to increase noise immunity if the system can tolerate the additional delay. The total delay time of the zero-crossing detection is 7.2 μs from the input filter plus the propagation delay of the comparator of 320 ns (maximum). The slew rate of the AC line voltage during the zero crossing is 360 VPK × 2 × π × 50 Hz = 113 mV/μs. The effective zero-crossing threshold therefore is 113 mV/μs × (7.2 μs + 320 ns) = 850 mV.
Table 7-2 summarizes the key parameters of the design.
PARAMETER | VALUE |
---|---|
Shunt resistor value R5 | 2.43 MΩ (5 × 487 kΩ) |
Maximum current through R5 | 148 μA |
Effective switching threshold | ±850 mV |
Propagation delay | <8 μs |