The UCC3890 controller is optimized for use as an off-line, low power, low voltage, regulated current supply, ideally suited for battery trickle charger applications. The unique circuit topology used in this device can be visualized as two cascaded flyback converters; each operating in the discontinuous mode, and both driven from a single external power switch. The significant benefit of this approach is the ability to charge low voltage batteries in off-line applications with no transformer, and low internal losses. The control algorithm used by the UCC3890 forces a switch on time inversely proportional to the input line voltage, while the switch off time is inversely proportional to the output voltage. This action is automatically controlled by an internal feedback loop and reference. The cascaded configuration allows a large voltage conversion ratio with reasonable switch duty cycle.