Cross regulation in flyback converters: solutions

Studies at UCI have shown that cross regulation in multiple output flyback converters can be significantly improved when the clamp voltage is lowered to slightly above the reflected output voltage. In this paper, three solutions for reducing the clamp voltage are investigated. In a conventional RC clamp, the clamp voltage can be reduced by decreasing its resistor value, but this leads to higher power losses. A new operating condition for the nondissipative LC snubber is found to achieve the goal by setting its resonant frequency below the switching frequency. In addition, a simple passive energy regenerative clamp is proposed that allows the clamp voltage to be lower than that of the RC clamp, thus improving the cross regulation without using an extra inductor as in the nondissipative LC snubber.