DER-228: 12V @ 1.25A, 85 ~ 265VAC in


This report describes a universal input, 12 V, 1.25 A flyback power supply using a TNY278P device from the TinySwitch-III family of ICs. The goal of the design was to demonstrate the very low no-load input power that is achievable with TinySwitch-III devices.

The design was based on the EP91 reference design board with the only changes being optimization of the bias winding components that supply the operating current into the BYPASS pin of the TNY278P IC and changing the output diode from a PN ultra-fast to Schottky barrier type.

The report contains the complete specification of the power supply, a detailed circuit diagram, the entire bill of materials required to build the supply, extensive documentation of the power transformer, along with test data and oscillographs of the most important electrical waveforms. The board provides a number of user configurable options which are designed to demonstrate the features and flexibility of the TinySwitch-III family. These include easy adjustment of the device current limit for increased output power or higher efficiency operation, and a latched output overvoltage shutdown.


Manufacturer Power Integrations
Category AC/DC and DC/DC Conversion
Sub-Category AC/DC SMPS - Single Output
Eval Board -
AC Voltage 115 V
230 V
Universal (115 / 230V)
Outputs and Type 1 Isolated
Voltage Out 12 V
Current Out 1.25 A
Output Power 15 W
Features Current Limit (Adj. or Fixed)
Frequency Jitter for EMI
Open Circuit Protection
Over Voltage Protection
Short Circuit Protection
Under Voltage Protection, Brown-Out
Efficiency @ Conditions >82%, 85 VAC, 12V @ 0.125 ~ 0.875 A
>82%, 230 VAC, 12V @ 0.6 ~ 1.25 A
>82%, 115 VAC, 12V @ 0.125 ~ 1.25 A
>81%, 265 VAC, 12V @ 0.6 ~ 1.25 A
No-load Input Power @ Voltage 30 mW @ 230 VAC
Switching Frequency 132 kHz
Internal Switch Yes
Component Count + Extras 26 + 6
Voltage In 85 ~ 265 VAC
Design Author Power Integrations
Application / Target Market AC Adapters
Auxiliary Power Supply
Battery Chargers
Cellular Phone
DVD/Blu-ray Players
Industrial Power
MP3 Players
White Goods
Main I.C. Base Part TNY278
Date Created By Author 2009-11
Date Added To Library 2020-05

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