Automatic X Capacitor Discharge IC

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Figure 1. Typical Application – Not a Simplified Circuit.

Data Sheets

Product Details

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.


Key Features

  • Blocks current through X capacitor discharge resistors when AC voltage is connected
  • Automatically discharges X capacitors through discharge resistors when AC is disconnected
  • Simplifies EMI filter design – larger X capacitor allows smaller inductive components with no change in consumption
  • Only two terminals – meets safety standards for use before or after system input fuse
  • >4 mm creepage on package and pcb
  • Self supplied – no external bias required
  • High common mode surge immunity – no external ground connection
  • High differential surge withstand – 1000 V internal MOSFETs

EcoSmart® – Energy Efficient

  • <5 mW consumption at 230 VAC for all X capacitor values


  • All ACDC converters with X capacitors >100 nF
  • Appliances requiring EuP Lot 6 compliance
  • Adapters requiring ultra low no-load consumption
  • All converters requiring very low standby power

*IEC62301 Clause 4.5 rounds standby power use below 5 mW to zero.

Component Selection Guide

Product2BVDSSMax Total X CapacitanceTotal
(R1 + R2)
825 V
1000 V
500 nF 1.5 MΩ
825 V
1000 V
750 nF 1.02 MΩ
825 V
1000 V
1 µF 780 kΩ
825 V
1000 V
1.5 µF 480 kΩ
825 V
1000 V
2 µF 360 kΩ
825 V
1000 V
2.5 µF 300 kΩ
825 V
1000 V
3.5 µF 200 kΩ
825 V
1000 V
5 µF 150 kΩ


  1. Values are nominal. RC time constant is <1 second with ±20% X capacitor and ±5% REXT from these nominal values.
  2. Packages: D: SO-8.

Product Documents

Design Examples

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