Application Report
SLVA666 –April 2014
Isolated Multiple Output Flyback Converter Design
Using TL494
SrivatsaRaghunath
ABSTRACT
The TL494 is one of the earliest pulse-width-modulation (PWM) controllers used in switched mode power
supplies. It incorporates all the functions required in the construction of a PWM control circuit on a single
chip. Designed primarily for power-supply control, this device offers the flexibility to tailor the power-supply
control circuitry to a specific application. This application report discusses building a multiple-output low-
cost isolated flyback converter with the TL494. Component selection and magnetics design is also shown.
Before current mode control was successfully implemented, the TL494 PWM mode ensured low EMI and
noise operation due to its trailing edge modulation technique. The power supply is designed for +5-, +15-,
and +15-V outputs. It is self-contained with overcurrent and overvoltage protections, and the PI controller
is designed to limit the highest power output. Each stage of the flyback converter design and component
selection is explained. A MathCAD file is available along with this document, which helps in design
calculation.
Topic ........................................................................................................................... Page
1 Specifications...................................................................................................... 2
2 Transformer Design ............................................................................................. 3
3 Wire Gauge Selection ........................................................................................... 4
4 Window Area Check............................................................................................. 5
5 Snubber Design................................................................................................... 6
6 Output Capacitor Design ...................................................................................... 7
7 Soft Start Circuit.................................................................................................. 7
8 Compensator Design............................................................................................ 8
9 Gate Drive ......................................................................................................... 11
10 Current Limit ..................................................................................................... 11
11 Final Circuit Diagram ......................................................................................... 12
12 Test Results ...................................................................................................... 13
13 Conclusion........................................................................................................ 24
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SLVA666 –April 2014 Isolated Multiple Output Flyback Converter Design Using TL494
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