AP3706/08N uses Pulse Frequency Modulation
(PFM) method to realize Discontinuous Conduction
Mode (DCM) operation for flyback power supplies;
uses Primary Side Regulation (PSR) to provide Constant
Voltage (CV) and Constant Current (CC) regulation.
The principle of PFM is different from that of
Pulse Width Modulation (PWM), so the design steps of
the transformer for PFM operation is also different
from that for PWM operation. In the other side,
AP3706/08N uses PSR to provide CV/CC regulation
without requiring opto-coupler and loop compensation,
which makes the design of transformer more critical
than that with PWM. The following design steps
focus on the transformer design. Some design guides
to select diodes and transistor are also included.