MAXREFDES1249: Miniature Universal Input 36W AC-DC Flyback Converter using the MAX17595

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Input Type VIN (MIN)
Isolated/Non-Isolated Topology
AC 85 305 0.75 Single 48 36 Isolated Flyback

Flyback converters are the preferred topology in the SMPS (switched-mode power supply) for medium- and low-power range applications because they are simple and economic. They have less components and are efficient in isolating the output from input. They are used in battery-powered applications, universal AC/DC converters, and industrial and telecommunication equipment. Isolated converters traditionally regulate the output voltage and current by utilizing a secondary side regulation (SSR) composed of an optocoupler and secondary error amplifier.

The MAXREFDES1249 is a universal input (86V to 305V AC) offline-isolated power supply that works across all geographical regions. It delivers 36W DC at 48V suitable for Power over Ethernet (PoE) and telecommunication applications.

The design uses a MAX17595 peak-current-mode controller operated in the discontinuous conduction mode (DCM) of the flyback topology. The architecture efficiently regulates the output by utilizing the feedback network and current-sense, and controlling the duty cycle of the switching MOSFET (metal-oxide semiconductor field-effect transistor) for compact and cost-effective power conversion.

Key Features

  • Programmable frequency dithering for a low-EMI (electromagnetic interference) spread-spectrum operation
  • Programmable switching frequency optimizes the magnetic and filter components for compact, cost-effective, and efficient isolated/non-isolated power supplies
  • Isolation of 4000V AC between the primary and secondary sides
  • EMI and EMC (electromagnetic compatibility) compliant design
  • Programmable input enable/UVLO (undervoltage lockout) feature
  • Programmable input overvoltage protection
  • Adjustable soft-start
  • Hiccup-mode, short-circuit protection
  • Fast cycle-by-cycle peak current limit
  • Thermal shutdown protection
  • Space-saving, 16-pin, 3mm x 3mm TQFN (thin quad flat no-leads) package
  • Operating temperature range of -40°C to +125°C
MAXREFDES1249 Board Enlarge+

Designed, Built, Tested

This document describes the hardware above. It is a detailed, systematic technical guide to design an isolated no-opto flyback DC-DC converter using Maxim’s MAX17595 controller. The power supply was built and tested.


PCB Layout

Test Results


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