SNVSBZ3 June 2021 LM5168-Q1
The secondary output should have a "dummy" load connected at all times to prevent the output voltage from rising too high under certain conditions. Since the secondary output is not tightly regulated by the control loop, and because of transformer and diode parasitics, COUT2 can charge to high levels unless the energy is dissipated in the secondary output load. In this example, a 1-kΩ resistor is used as a minimum load on the secondary output. A Zener diode can also be used to clamp the secondary output voltage, if desired.