Many years ago, I wrote about my experience with the "smart" power adapter. As I changed my work notebook computer from Dell to HP, despite of same power rating and same 3-pin barrel plug, the HP computer would not detect the Dell power adapter. It seems such a waste not to have a common standard of power adapters. (The move towards USB C PD for all mobile devices should make thing better.) So I decide to crack one open to see what exactly the center pin does. This is a 90-watt dell power adapter (19.5V 4.62A); it is not too hard to crack the case open. The power adapter is made in China by Delta Electronics, a Taiwanese power product company. The date code is "0731". The three wires go connections labelled VO, GND and DATA on the single layer PCB. The DATA trace is connected to a 3-pin TO-92 device, with marking "75M518E BYE TI". No information is found on this device, so it is likely a proprietary device. The DATA signal has an 130-Ohm resistor in series and is clamped by a Zener. The device is powered directly off the 19.5V.
The primary is switched by Infineon SPA15N65C3 650V 0.28-Ohm N-channel MOSFET. The secondary side is Vishay Siliconix SUP60N10 100V 0.02-Ohm N-channel MOSFET. The controller has the marking "DAP6A", which seems to be a custom specific device from ON Semi with the part no. DAP006, PWM Current−Mode Controller for Free Running Quasi−Resonant Operation and is equivalent to NCP1200. On the secondary side, there is an 8-pin IC with marking, "DAS001 ST", which appears to be equivalent to TSM103W, a dual opamp with 2.5V voltage reference.
When the power connector is plugged into the computer, the center pin is pulled up to about 3.3V. Then there is data activities on the line. If the center pin is not connected to the power adapter, the center pin from the computer toggles every 3 seconds with 2 seconds high.
When the center pin is not connected, the power draw drops to 20W and the computer runs at a slow clock rate (about 800MHz).
