Isolated 40W Power Supply Reference Design

The design transforms 24V into multiple voltage rails, utilizes active-clamp topology, and improves both compactness and cost-effectiveness.

An isolated power supply is a critical component in modern electronic systems, providing numerous essential benefits that ensure the safe and efficient operation of various applications. By creating a physical barrier between the input and output, isolated power supplies enhance safety by protecting users and sensitive components from high voltage levels. They also play a vital role in reducing electrical noise and interference, preventing ground loops, and maintaining signal integrity, which is crucial for the performance and reliability of sensitive electronic equipment. Maxim’s isolated power supply reference design efficiently converts 24V into various useful voltage rails.

The MAXREFDES116# reference design showcases the MAX17599 low IQ, wide-input range, and active-clamp current-mode PWM controller. The MAX17599 integrates all necessary control circuitry to design wide-input, isolated forward-converter industrial power supplies. The reference design functions across a 17V to 36V input voltage range, delivering up to 8A at 5V output. It employs an active-clamp transformer reset topology for forward converters. It offers several benefits, including reduced voltage stress on the switching elements, the ability to use a smaller transformer due to a higher permissible flux swing, and enhanced efficiency by eliminating the need for dissipative snubber circuits. These advantages lead to a more compact and cost-effective isolated power supply. 

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The design operates at a switching frequency of 350kHz. For applications sensitive to electromagnetic interference, the design includes a frequency-dithering feature for low-EMI spread-spectrum operation. The pin spacing measures 15.24mm (0.6in) from power to ground and 50.8mm (2in) from the input side to the output side.

The design incorporates an input-undervoltage lockout (EN/UVLO) for setting the startup voltage of the input supply (preset to 16.5V) and maintaining proper function during brownout conditions. The EN/UVLO is also used to toggle the IC on and off. Overvoltage-input (OVI) protection ensures the controller shuts down if the input supply exceeds 37.0V.

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The design features a soft-start (SS) pin to manage inrush current and adjust the soft-start duration. Additionally, hiccup mode overcurrent protection minimizes power dissipation during fault conditions. A soft-stop function safely discharges the clamp capacitor when powered off, facilitating a controlled restart.

Further, a negative current limit in the current-sense circuitry helps to restrict clamp-switch current under dynamic conditions. Overtemperature faults trigger a thermal shutdown for dependable device protection.

With the components provided, the reference design achieves a peak efficiency of 91.5% at an input voltage of 24V. This versatile power solution is suitable for various applications, including programmable logic controllers (PLC), industrial process control, industrial sensors, telecom/datacom power supplies, isolated battery chargers, servers, and embedded computing systems.

The reference design has undergone rigorous testing for load and line regulation, efficiency, and transient response. Like all Maxim reference designs, the bill of materials (BOM), schematics, layout files, and Gerber files are accessible for download under the Design Resources tab. Additionally, boards, including through-hole pins for quick placement and rapid prototyping, can be purchased. To read more about this reference design, click here.