The TPS7A78 looks ideal for an application we have for a wireless device where we have previously used a cap dropper circuit or a cap dropper followed by a buck converter (TPS54601).
I'd just like to clarify the device efficiency.
In a conventional cap dropper a Zener diode clamps the rectified voltage. Current that passes through Cs and is not used by the application is dissipated as heat in the Zener. The power consumed by the circuit is fixed by the value of Cs whether it is used or not.
Am I right in understanding that the TPS7A78 shunts excess current via the controlled bridge back into the AC supply? The apparent power will remain unaffected by this but the real power consumed by the application will be reduced?