The TPS7A78 improves the overall efficiency and standby-power in power-supplies in an
easy-to-use, non-magnetic approach to AC/DC conversion. The TPS7A78 uses a capacitor-drop
architecture to lower the AC source voltage before actively clamping the rectified voltage. The
device then regulates this rectified voltage down to the application-specific operating voltage.
The unique architecture of the device allows the standby power to be reduced to just a few 10s of
milliwatts. The TPS7A78 switched-capacitor stage reduces power losses by stepping down the
rectified input voltage by a factor of four and increasing the output-to-input current by the same
ratio, as given by PIN ≅ POUT and
VIN ≅ VOUT × 4. Compared to a traditional
capacitor-drop (cap-drop) stage, this step down reduces input current, thus minimizing the value of
the capacitance needed.
Electricity-metering applications, where the power supply must be reliable and magnetic
tamper-proof, benefits from using the TPS7A78 because this device does not require external
magnetics. This feature makes complying with IEC 61000-4-8 easier while minimizing magnetic
Additionally, the TPS7A78 also comes with a user-programmable, power-fail detection
threshold that can provide an early alert to power failures and enable shutdown before complete
power loss. The power-good indicator (PG) is also provided for sequencing or resetting a
The TPS7A78 is available in a 14-pin HTSSOP (PWP) package.