65W notebook laptop power adapter circuit

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. 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 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.