SBVS343A March 2019 – September 2019 TPS7A78
The peak AC supply voltage for this example is equal to 375 V (√2 × 265) and the electrical fast transient immunity (EFT) requirement is given as 1 kV. Thus, a TVS with a maximum clamping voltage of 1000 V can be used. Equation 11 shows the calculated RS (MIN) value.
Because both the device IPEAK current and the device maximum ISHUNT current flow through RS, the power rating of RS must be able to handle these currents values. See the Checking for the Device Maximum ISHUNT Current section for the ISHUNT current calculation and RS power rating for this application.
If the application already has an upstream hot-plug current-limit circuit, then the requirement for the surge resistor can be relaxed to significantly improve the solution standby-power; see the Standby Power and Output Efficiency section for details.