Snubber capacitor to safeguard HiperPFS B(Vdss) of 530V?
Page 18 of the HiperPFS Boost PFC controller datasheet says that a 33-100pF capacitor should be connected across the Boost PFC diode in order to prevent the internal FET’s B(Vdss) of 530V from being breached.
Page 18 says that the 530V level is most likely to be breached during heavy loading of the Boost output to almost the overload level.
How can such a capacitor be of any use? Surely it would just create more circuit noise due to high di/dt as such a snubber capacitor gets rapidly charged/discharged?
How could the drain of the internal FET go up to 530V?....As soon as the drain voltage goes above Vout then the Boost diode will clamp the drain voltage to vout…..which wouldn’t get anywhere near 530V.
The only way the drain could get up to 530V would be due to PCB trace stray inductance…but this should be minimised with tight layout and having a small value ceramic cap right at the internal boost diode cathode going down to the controller’s star ground point with the power ground.