How to choose a suitable AC-DC power adapter?

Selecting a suitable AC-DC power adapter requires considering multiple aspects. Firstly, determine the output power of the power supply according to the power requirements of the device. Ensure that the power supply can meet the power needs of the device, and the output power should be slightly greater than the power requirement of the device to cope with situations such as device startup and instantaneous load.

In terms of output voltage and current, the output voltage and current of the power supply should match the voltage and current requirements of the device to ensure that the device can work normally. At the same time, indicators such as the load regulation performance and output ripple voltage of the power supply also need to be considered to ensure that the power supply provides stable power output. Indicators such as efficiency, power factor, and electromagnetic compatibility cannot be ignored. A high-efficiency power supply can reduce energy waste and improve the energy efficiency of the device; a good power factor can reduce the impact on the power grid and improve the efficiency of the power supply system; good electromagnetic compatibility performance can reduce the interference of the power supply to the device and the surrounding environment and ensure the stable operation of the device. In addition, some specific chip solutions can also be referred to.
For example, for the AC/DC adapter power chip U6117S, in the flyback primary-side feedback application, there are different typical power recommendations under different input voltages. U6117S is 7.5W at 230VAC and 5.5W at 85 - 265VAC. While the AC/DC adapter power chip U6117D is 15W at 230VAC and 12W at 85 - 265VAC. In the Buck step-down application, U6117S and U6117D also have different power performances.

Another example is the high-end power ic U25136 for adapters. It integrates multiple protection functions and can achieve high-performance constant voltage output performance. It is especially suitable for low-power offline charger applications. Using U25136 can work without abnormal noise and at the same time ensure excellent dynamic performance. By using the integrated line loss compensation function, high-performance constant voltage output performance can be obtained. There is also the AC/DC adapter power IC CY2525D. It uses a variable drive current method to drive the power switch tube to work to achieve lower switching loss and conduction loss to improve efficiency, and optimize the switching voltage and current spikes to achieve better EMI effects. It has main characteristics such as primary-side control without optocoupler and secondary control circuit, and PWM + PFM multi-mode hybrid control. In short, selecting an AC-DC power adapter requires comprehensive consideration of device power requirements, output voltage and current, efficiency and other indicators as well as specific chip solutions to ensure that the most suitable power adapter is selected.