The AP3103 is a low start-up current, current-mode
PWM controller with green-mode power-saving
operation. The PWM switching frequency at normal
operation is externally programmable and is trimmed
to a tight range. The dithering of frequency will
improve EMI feature. When the load decreases, the
frequency will reduce and when at a very low load, the
IC will enter the “burst mode” to minimize switching
loss. About 20kHz frequency switching is to avoid the
audible noise as well as reducing the standby loss.