PSU controller for ultra-low standby power in USB chargers

December 07, 2015 // By Graham Prophet
The AP3785T AC-DC primary-side switched-mode power supply controller from Diodes Inc. is aimed at 8W to 15W 5V output USB chargers that necessitate ultra-low standby power, to meet increasingly tight power supply efficiency regulations.

Various features contribute to the superior performance delivered by the AP3785T: a no-load input power rating of less than 10 mW; higher efficiency and better EMI result from valley-on operation and a low VCS jitter specification; higher conversion efficiency is also achieved when the AP3785T is used in conjunction with a synchronous rectifier, such as the AP4341. Multiple PWM/PFM control modes further help improve audio noise and efficiency.

Over-voltage protection, output short-circuit protection and transformer saturation protection (via primary peak-current limitation) are all built into the AP3785T. Internal temperature protection is also provided along with a dedicated pin to support external temperature protection. When operating as a constant current regulator, a feedback pin enables compensation for changes in line voltage whereas in constant voltage mode the AP3785T can compensate for voltage drops due to different cable lengths or gauge.

Offered in a standard pinout, SO-8 package, the AP3785T is priced at $0.38 (10,)))).