I have a power supply design using LNK626. The 4V output return is connected to the AC Neutral which is connected to the Negative of the Mains rectifier capacitor. The mains are half wave rectified to do this.
The output voltage feed back is a resistor divider from the 4V output winding similar to figure 12 in the linkcv_family_datasheet.
The total output capacitance is 570uf 6.3V made up of a polymer 470uf and a ceramic 100uf.
The observed problem is the droop in output voltage as the load is changed from 0.2amps to 1.4amps. The output voltage drops from 4V to 3.52 volts and recovers to 3.88volts. During the droop time the switching action of the primary switch is off as the LNK626 is operating in burst mode, 208us period.
The problem is worse at high input voltages ~ 265VAC. 96vac is not as much a problem.

Thus, the LNK626 does not know the output is low because the primary is not switching.

1. Is there a method to increase the burst mode frequency by reducing the number of pulses in each burst?

2. Is there another way to decrease the droop, other than increasing the output capacitance. The response time of the LNK626 is approximately 230us to start to recover.
My estimate for capacitance required to keep the droop to 100mv with a 1.2amp change in current within the 230us response time of the IC is 2,760uf.

3. I have tried the series R-C on the FB pin of the LNK626 to adjust the "pulse groupings" of burst mode without success.

4. The output also overshoots when the load current is decreased from 1.4 to 0.2amp. A file was uploaded that shows the overshoot on LNK626.

Richard Keller
rkeller@rakinc.com