Reference design sets out isolated 24V to 12V, 20W supply

Reference design sets out isolated 24V to 12V, 20W supply

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By Nick Flaherty

Each design has been tested for load and line regulation, as well as efficiency and transient performance: BOM, schematics, layout files, and Gerber files are all available in the Design Resources tab. Boards are available for purchase; most boards feature through-hole pins for immediate board placement and accelerated prototyping.

MAXREFDES113# is an efficient flyback topology with 24V input, and a 12V output at 20W of power (1.6A). The design features the MAX17596, a peak-current-mode converter with flexible switching frequency. This entire circuit fits on a 20 × 35mm board. A related design, MAXREFDES114, delivers 5V from 24V.

Maxim notes that, transformer selection is often the most difficult step in isolated power design. Multiple transformers (Halo Electronics TGSP-P153EP13LF, Wurth Electronics 750316112r01, HanRun HR051441, and Sumida 13324-T115) have been qualified for this design, simplifying the process of transformer selection. The reference design operates over a 17V to 36V input voltage range, and provides up to 1.6A (plus 20% overhead) at 12V output. The MAX17596 has an internal amplifier with 1% accurate reference, eliminating the need for an external reference. The switching frequency is programmable from 100 kHz to 1 MHz with an accuracy of 8%, allowing optimization of magnetic and filter components, resulting in compact and cost-effective power conversion. This design is set to switch at 200 kHz. For EMI-sensitive applications, the MAX17596 incorporates a programmable frequency dithering scheme, enabling low-EMI spread-spectrum operation.

Input undervoltage lockout (EN/UVLO) is provided for programming the input-supply start voltage (set to 17V in the design), and to ensure proper operation during brownout conditions. The EN/UVLO input is also used to turn on/off the IC. The overvoltage input (OVI) protection scheme is provided to make sure that the controller shuts down when the input supply exceeds its maximum allowed value (set to 36V in the design).

The reference design delivers a peak efficiency of 87% with the supplied components when the input is 24V. Use it, Maxim suggests, in programmable logic controllers (PLC), industrial process control, industrial sensors, telecom power supplies, isolated battery chargers, servers, and embedded computing.

Maxim Integrated:


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