TPS7A78 – 120-mA smart cap-drop low-dropout (LDO) linear voltage regulator

TPS7A78 – 120-mA smart cap-drop low-dropout (LDO) linear voltage regulator

Texas Instruments TPS7A78 Low-Dropout (LDO) Linear Regulator 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 shielding cost. 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 microcontroller.


  • Non-isolated power solution for ≥ 18VAC RMS
    • Up to 75% efficiency
    • 15mW (typical) standby power consumption
    • Line-voltage, cap-drop capacitor as small as 1/4th the size of linear solutions
  • Available in fixed output voltages
    • 1.3V to 5V (50mV steps)
  • Power-fail detection
  • Power-good indication
  • 1% typical accuracy
  • Package
    • 5mm x 6.5mm HTSSOP-14 (PWP)

Block Diagram

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Mike is the founder and editor of, an electronics engineering community/news and project sharing platform. He studied Electronics and Physics and enjoys everything that has moving electrons and fun. His interests lying on solar cells, microcontrollers and switchmode power supplies. Feel free to reach him for feedback, random tips or just to say hello :-)

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