When AC voltage is applied, CAPZero blocks current flow in the X capacitor safety discharge resistors, reducing the power loss to less than 5 mW, or essentially zero* at 230 VAC. When AC voltage is disconnected, CAPZero automatically discharges the X capacitor by connecting the bleed resistors in parallel. This operation allows total flexibility in the choice of the X capacitor to optimize differential mode EMI filtering and reduce inductor costs, with no change in power consumption.
Designing with CAPZero is simply a matter of selecting the appropriate CAPZero device and external resistor values in Table 1 for the X capacitor value being used. This design choice will provide a worst case RC time constant, when the AC supply is disconnected, of less than 1 second as required by international safety standards.
The simplicity and ruggedness of the two terminal CAPZero chip makes it an ideal choice in systems designed to meet EuP Lot 6 requirements.
The CAPZero family has two voltage grades: 825 V is used when an MOV is connected in parallel to the X capacitor in Figure 1. 1000 V is used when the MOV is placed elsewhere in the system in combination with differential surge voltage requirements of >1.5 kV. See Key Applications Considerations section for details.
*IEC62301 Clause 4.5 rounds standby power use below 5 mW to zero.