New CAPZero ICs Automatically and Safely Discharge X Capacitors

Jun 9, 2010 4:05 PM

Power Integrations has launched CAPZero, a family of innovative, two-terminal, automatic X capacitor discharge ICs that eliminate power losses while allowing power supplies to comply with safety standards.

X capacitors are typically positioned across a power supply's input terminals to filter differential EMI noise. Alone, these components could present a safety hazard because they can store unsafe levels of high-voltage energy for long periods of time after the AC is disconnected. To meet safety standards, resistors are commonly used in parallel with the X capacitor and across the AC line to provide a discharge path. However, these discharge resistors produce a constant power loss while the AC is connected and are a significant contributor to no-load and standby input power consumption.

CAPZero acts as a smart high-voltage switch when placed in series with discharge resistors. When AC voltage is applied, CAPZero blocks current flow in the X capacitor safety discharge resistors, reducing the power wasted in these components to zero at 230 VAC. When the AC voltage is disconnected, CAPZero automatically and safely discharges the X capacitor by closing the circuit through the bleed resistors and directing the energy away from the exposed AC plug. This approach provides engineers with total flexibility in their choice of the X capacitor used to optimize differential-mode EMI filtering without worrying about the effect of the required bleed resistors on system no-load and standby power budget. The innovative two-terminal design inherently meets international safety standards for all open and short-circuit fault tests, allowing CAPZero to be used before or after the system input fuse.

CAPZero is suitable for all AC-DC converters with X capacitors that require very low standby power, and is offered with 825 V or 1000 V MOSFETs to support a variety of power supply design needs. It is ideal for a wide range of applications, including PCs, servers/workstations, monitors and TVs, printers and notebooks, as well as appliances requiring EuP Lot 6 compliance and adapters requiring ultra-low no-load consumption.

CAPZero devices are available now in an SO-8 package at $0.40 each for 10,000-piece quantities.

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