ZHCS779C March 2012 – July 2025 UCC28070 , UCC28070A
PRODUCTION DATA
The value of the output capacitor is governed by the required hold-up time and the allowable ripple voltage on the output.
The hold-up time depends on the load current and the minimum acceptable voltage at the output.
The value of the output capacitor must be large enough to provide the required hold-up time and keep the ripple voltage at twice-line frequency within acceptable limits. Normally a capacitance value of about 0.6μF per Watt of output power (for ~400V output) is a reasonable compromise where hold-up time is not significant. At 300W this would indicate a capacitance of about 200μF.
The low-frequency (at twice-line frequency) rms voltage ripple on VOUT is given by Equation 49:
The resulting twice-line low-frequency current in the capacitor is: