RS Components (RS), a leading distributor for engineers, is now stocking the CapZero family of automatic discharge ICs from Power Integrations, which eliminate the energy losses incurred when using resistors alone to discharge the X capacitors of mains-powered equipment safely.
X capacitors connected from line to line at the AC input stop electromagnetic interference going back onto the grid. New safety standards such as IEC 62368-1 place increasing importance on discharging capacitors when power is removed, to prevent risk of electric shock. A parallel resistor is effective, but can dissipate around 20mW or more even during standby or power-off modes. This hinders meeting eco-design standards such as external power supply regulations and ErP Lot 6.
Inserting a Power Integrations CapZero IC in series blocks current to the resistor while the AC supply is connected, reducing power loss to less than 5mW. When the supply is disconnected, CapZero activates allowing the capacitor to discharge with a time constant less than one second.
CapZero not only saves power, but also allows the use of larger X capacitance values to increase EMI suppression. The family of ICs allows designers to select the right device to work with total X capacitance from below 500nF to as much as 5µF. 825V or 1000V voltage grades are available, giving flexibility to meet various surge requirements.