Features · Transformer offline power supply · Wide allowable input range for 400VDC to 100VDC · Fixed 5VDC or adjustable low voltage output · Output 200mA sink, source 150mA MOSFET gate to one · Use low cost SMD inductor · Short circuit protection · Optional isolation capability

describe
The UCC3888 controller is optimized for an off-line, low power, low voltage, regulated bias supply. With the unique circuit topology, this device can be imagined as two cascaded flyback converters, each driven from a single external power switch in continuous operation mode. The significant benefit of this approach is the ability to achieve voltage conversion rates up to 400V with a transformerless internal loss as low as 2.7. The control algorithm of the UCC3888 utilizes a switch set time inversely proportional to the input voltage, and a set switch time inversely proportional to the output voltage. This action is controlled by an internal automatic feedback loop and reference. The cascade configuration feature enables voltage conversion from 400V to 2.7V up to 7.6% with a switching duty cycle. This topology also provides inherent short-circuit protection for the output voltage to drop to zero, and the off-time tends to infinity for switching. The output voltage is set internally at 5V. It can be programmed to other output voltages with two external resistors. An isolated version to achieve this topology is described in U-149 for further instructions on the Unitrode application. ...