System Board 6884

MAXREFDES1227: Miniature 24W, 12V DC-DC Flyback Converter Using MAX17596

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Input Type VIN (MIN)
Isolated/Non-Isolated Topology
DC 17 60 2 Single 12 24 Isolated Fly Back

The MAXREFDES1227 is a miniature 12V output isolated power supply that can deliver up to 2A load current. The design employs the MAX17596 peak-current-mode controller in discontinuous-conduction mode (DCM) flyback topology running at 125kHz. The input voltage range of MAX17596 is 4.5V to 36V; however, an extra bias winding from the transformer is used to power the controller. This allows an input operating voltage of up to 60V for this design.

The transformer provides a galvanic isolation of 1500VRMS between the primary and the secondary. In addition, an optocoupler is used to provide secondary side feedback to the controller for voltage regulation while maintaining isolation. This document also discusses a step-by-step procedure that is used to implement this reference design. Design equations for the calculation of all the design parameters are presented. These equations show how the component values were calculated enabling users to modify this design for their applications.

Key Features

  • Miniature Design Optimized for Small Size
  • 17V to 60V Input Range
  • Isolated Output of 12V DC at 24W
  • Cycle-by-Cycle Current Limit
  • Resistor Programmable UVLO/OVI Threshold
  • Low-Cost DCM Flyback Design
  • Galvanic Isolation up to 1500VRMS
  • Proven PCB Layout
  • Fully Assembled and Tested
MAXREFDES1227 Board Enlarge+

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Designed, Built, Tested

This document describes the hardware shown above. It provides a detailed systematic technical guide to designing a DC-DC DCM flyback using Maxim’s MAX17596 current-mode controller. The power supply has been built and tested, details of which follow later in this document.

Design Resources


Peak-Current-Mode Controllers for Flyback and Boost Regulators

  • Programmable Switching Frequency Allows Optimization of the Magnetic and Filter Components, Resulting in Compact, Cost-Effective, Efficient Isolated/Non-Isolated Power Supplies
  • Programmable Frequency Dithering Enables Low-EMI Spread-Spectrum Operation
  • Integrated Protection Features Enhance System Reliability