Lac781p Schematic Top [work] — Verified Source

+-----------------+ | | AC IN ~ | | | [Bridge Rectifier] | | | +-------+---------+ | C1 + (Large Electrolytic, e.g., 2200µF/25V) | +-----> Vin (LAC781P Pin 1) | GND ---+-----> GND (LAC781P Pin 2) | +-----> Common Ground Vout (LAC781P Pin 3) ---> +12V Output | C2 + (Electrolytic, 100µF/16V) | C3 + (Ceramic, 0.1µF) | GND

| Component | Value | Purpose | |-----------|---------|-------------------------------------------------------------------------| | C1 | 2200µF | Bulk input smoothing; reduces ripple from rectified AC. | | C2 | 100µF | Output filtering; improves transient response. | | C3 | 0.1µF | High-frequency decoupling; suppresses oscillations. | | D1-D4 | 1N4007 | Bridge rectifier (if AC input is used). | | LAC781P | - | +12V fixed regulator with internal current limiting and thermal shutdown. | lac781p schematic top

The top or "top-level" schematic for the LAC781P would typically include: +-----------------+ | | AC IN ~ | |

A poor layout that ignores the internal paths shown in the schematic top will cause high-frequency oscillation, excessive output ripple, or premature thermal shutdown. | | D1-D4 | 1N4007 | Bridge rectifier (if AC input is used)

When someone searches for they often need the PCB top layer information. Here is a typical layout recommendation for a single-sided or two-layer board.

If the gate voltage is missing, the BQ25A (pin 4, ACDRV) may not be outputting the required ~25V boost to open the MOSFET. Step-Down (+3V/+5V) Section: Verify +3VALW at the RTC cell and battery connectors.