MAXREFDES1037: 72W offline flyback converter

The MAX17595 is a peak-current-mode controller for designing wide input-voltage flyback regulators. The MAX17595 offers optimized input thresholds for universal input AC-DC converters and telecom DC-DC (36V to 72V input range) power supplies. It contains a built-in gate driver for an external n-channel MOSFET. The MAX17595 houses an internal error amplifier with 1% accurate reference, eliminating the need for an external reference. The switching frequency is programmable from 100kHz to 1MHz with an accuracy of 8%, allowing optimization of magnetic and filter components, resulting in compact and cost-effective power conversion. For EMI-sensitive applications, the MAX17595 incorporates a programmable frequency dithering scheme, enabling low-EMI spread-spectrum operation. Users can start the power supply precisely at the desired input voltage, implement input overvoltage protection, and program soft-start time. A programmable slope compensation scheme is provided to ensure stability of the peak current-mode control scheme. Hiccup-mode overcurrent protection and thermal shutdown are provided to minimize dissipation in overcurrent and overtemperature fault conditions.

Key Features

• Programmable Switching Frequency Allows Optimization of the Magnetic and Filter Components, Resulting in Compact, Cost-Effective, Efficient Isolated/ Nonisolated Power Supplies
• 00kHz to 1MHz Programmable Switching Frequency with Optional Synchronization
• Peak Current Mode Control Provides Excellent Transient Response—Offline (Universal Input AC) and Telecom (36V to 72V) Flyback Controller
• Programmable Frequency Dithering Enables Low EMI Spread-Spectrum Operation
• Integrated Protection Features Enhance System Reliability
• Adjustable Current Limit with External Current Sense Resistor
• Fast Cycle-By-Cycle Peak Current Limiting Hiccup-Mode Short-Circuit Protection
• Overtemperature Protection
• Programmable Soft-Start and Slope Compensation
• Input Overvoltage Protection

This board is not available for purchase.

An offline DCM flyback converter using the MAX17595 is demonstrated for a 24V DC output application. The power supply delivers up to 3A at 24V.

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to designing an offline discontinuous conduction mode (DCM) flyback using Maxim’s MAX17595 current-mode controller. The power supply has been built and tested, details of which follow later in this document.

Design Resources