Primary-side switcher cuts power supply parts count

September 05, 2014 // By Graham Prophet
AP3988 is an off-line, side-switching controller designed to cut costs and improve power supply performance in chargers, ADSL adapters and home appliance supplies. By providing primary-side control, the device eliminates the requirement for opto-couplers and secondary-side control circuitry, reducing component count, board space requirements and cost.

The AP3988 controller is designed for use in 5.5W adapters: it regulates output voltage using piece-wide pulse frequency modulation, in which analogue levels are represented as fixed-duration pulses of varying repetition rate. Transistors with 700 VCBO are built into the device and start-up current is typically 0.2 µA. This switcher has integral cable voltage drop compensation of 5% of nominal voltage and adjustable line voltage compensation and is offered in the SO-7 package.

Primary-side regulation results in higher efficiency, along with improved output voltage and current accuracy, enhanced over-voltage and short-circuit protection, and better EMC performance, achieved by frequency dithering.

Diodes Inc.; www.diodes.com