Low-cost flyback solutions for 10-mW standby power

For low-power AC/DC conversion, flyback topology remains the preferred choice due to its simplicity and low cost. Using a small number of external components, this topology can provide one or more outputs for a very wide input voltage range. It is used in isolated and non-isolated forms to cover a broad range of applications, such as battery chargers in smartphones and tablets; auxiliary power supplies in TVs, desktop computers, and home appliances; AC adapters for portable computing, set-top boxes, and networking; and many more.

In most applications, flyback converters are stand-alone external power supplies in wall chargers/adapters. In some cases they are powering either a portion of larger equipment or providing standby power to maintain system functions like the user display and remote control when the equipment is not performing its primary function. In all cases, the standby-power consumption of the flyback converter is being heavily scrutinized to minimise the overall power drain when it seems the converter is doing nothing. For example, a flyback power supply used in an AC wall charger may have a mass-production specification of less than 30 mW. If the actual supply consumes only 10 mW of standby power, the 20-mW difference can allow a higher margin for leaky circuit components such as input filters, capacitors, and bias components, reducing overall solution cost. Similarly, a flyback converter with low standby-power consumption can allow more system functions to be active in standby mode while keeping the end equipment's total power consumption to a minimum.

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Originally published by Texas Instruments Inc. at www.ti.com as "Low-cost flyback solutions for 10-mW standby power".