System Board 6828

MAXREFDES1085: Miniature 24W DC-DC Flyback Converter Using the MAX17596

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Input Type VIN (MIN)
Isolated/Non-Isolated Topology
DC 17 60 1 Single 24 24 Isolated Flyback

The MAXREFDES1085 is a miniature, 24V output, isolated power supply that can deliver up to 1A of load current. The design uses the MAX17596 peak-current-mode controller in discontinuous-conduction mode (DCM) flyback topology running at 125kHz. The input voltage range of the MAX17596 is 4.5V to 36V. However, an extra bias winding from the transformer is used to power the controller. This allows the input operating voltage to go 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 to implement this reference design and presents design equations for the calculation of all the design parameters. These equations show how to calculate the component values to allow users to modify this design for their applications.

Key Features

  • Miniature design optimized for small size
  • 17V to 60V Input Range
  • Isolated Output of 24V 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
MAXREFDES1085 Board Enlarge+

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Designed, Built, Tested

This document describes the hardware shown in above. It provides a detailed systematic technical guide to designing a DC-DC discontinuous conduction mode (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