JAJSFD2A May 2018 – June 2018 OPA521
PRODUCTION DATA.
The high-voltage capacitor (HV Cap) blocks the low-frequency mains voltage by forming a voltage divider with the winding inductance of the line coupling transformer. In many applications, a maximum reactive power (VA limit) on the HV Cap may be required. To meet this requirement, the HV Cap value is calculated by Equation 1.
For a 240-VAC, 50-Hz application with a 10-VA limit, the maximum value for the HV Cap is shown in Equation 2.
A 470-nF capacitor is frequently used in these types of applications. A metallized polypropylene electromagnetic interference and radio frequency interference (EMI/RFI) suppression capacitor is recommended because of the low loss factor associated with the dielectric, which results in minimal internal self-heating. Operating the capacitor at approximately 80% of its ac-rated voltage ensures a long component operating life. See Circuit Protection of this document for additional discussion on selecting the correct HV Cap value to withstand impulses on the mains.