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Low-Power Universal-Input Power Supply Achieves High Efficiency

Expanding global markets have created a demand for what have become known as universal-input power supplies –– that is, power supplies that allow devices to be plugged into wall outlets anywhere in the world. These power supplies must be able to operate directly from 100-, 110-, and 220-V ac power lines without the use of selector switches or jumpers. A power supply with the ability to operate under such conditions while remaining cost-effective is now becoming a necessity.

In the under 30-W power range, meeting the above requirements while maintaining high efficiency has been a challenge. Add to this the need to meet various international safety standards, and the circuit designer has his hands full.

The demands of low-power universal-input power supplies are met by the Si9120 pulse width modulation (PWM) controller from Vishay Siliconix. Using the Si9120, the flyback circuit presented in this application note demonstrates that designing universal-input supplies can be a simple task.