Lac781p - Schematic Top

The heavy lifting is done by a Darlington pair (or a single high-power NPN). This transistor operates in linear mode, dropping the excess voltage between input and output as heat. The schematic top shows this transistor connected between Input (collector) and Output (emitter), with its base driven by the error amp.

Integrated Radeon HD graphics or dedicated GPU variants like the HD 8600 2GB. Power Rail: Uses a 19V main power rail (VIN circuit). lac781p schematic top

The schematic outlines several vital power Rails and ICs required for the laptop to boot: The heavy lifting is done by a Darlington

: Verifying 19V input at the DC jack and through the first two MOSFETs. Integrated Radeon HD graphics or dedicated GPU variants

The output pin is directly connected to the emitter of the pass transistor. From the schematic top, you also see a discharge path (a resistor to ground) that ensures the output voltage falls quickly when input power is removed, preventing latch-up conditions.

The 3V RTC cell power is active even before the charger is connected.

Typically uses the bq24725A (labeled bq25A) to manage power input and battery charging.