65W notebook laptop power adapter circuit
This laptop power adapter circuit is designed using TOP269EG off-line switcher IC, (U1), used in a flyback configuration.
TOP269EG IC has an integrated 725 V MOSFET and a multi-mode controller. It regulates the output by adjusting the MOSFET duty cycle, based on the current fed into its CONTROL pin.
This laptop power adapter circuit will provide a fixed 19 volts output voltage at a maximum current of 3.5A.
The TOP269EG laptop power adapter circuit accepts an input voltage range between 90 and 265VAC.
Common-mode inductors L3 and L4 provide filtering on the AC input. X class capacitor C1 provides differential filtering, and resistors R1 and R2 provide safety from shock if the AC is removed, by ensuring a path for C1 to discharge. This is required by safety agencies when the capacitor value exceeds 100 nF. Bridge rectifier D1 rectifies the AC input, and bulk capacitor C2 filters the DC.
Y capacitor C11, connected between the primary and secondary side provides common mode filtering.
Capacitor C7 provides the auto-restart timing for U1. At startup this capacitor is charged through the DRAIN (D) pin. Once it is charged U1 begins to switch. Capacitor C7 stores
enough energy to ensure the power supply starts up. After start-up the bias winding
powers the controller via the CONTROL pin. Bypass capacitor C6 is placed as physically close as possible to U1.
U1 utilizes an output overvoltage shutdown function. An increase in output voltage causes an increase in the bias winding on the primary side, sensed by VR1. A sufficient rise in the bias voltage causes VR1 to conduct and bias Q1 to inject current into the Voltage Monitor (V) pin of U1. When the current exceeds 336 uA, U1 enters the overvoltage shutdown mode and latches off.