MAXREFDES115A#: 5V @ 4A, 18 ~ 36V in, Isolated Flyback Converter

MAXREFDES115x# is an efficient active clamp topology design with 24V input, and a 5V at 4A (20W) of power. The design features the MAX17599, an active clamp, current-mode PWM controller optimized for industrial supplies; this entire circuit fits on a 20mm x 55mm PCB.

This reset topology has several advantages including reduced voltage stress on the switches, transformer size reduction due to larger allowable flux swing, and improved efficiency due to elimination of dissipative snubber circuitry. These features result in a compact and cost-effective isolated power supply. The design is set to switch at 250kHz. For EMI-sensitive applications, the user can program the frequency-dithering scheme, enabling low-EMI spread-spectrum operation.

The input undervoltage lockout (EN/UVLO) is provided for programming the input-supply start voltage (set to 16.5V 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 the maximum allowed value (set to 37.0V in this design).

To control inrush current, the device incorporates a soft-start (SS) pin to set the soft-start time for the regulator. Power dissipation under fault conditions is minimized by hiccup overcurrent protection (hiccup mode). The SS feature provides safe discharging of the clamp capacitor when the device is turned off, and allows the controller to restart in a well controlled manner.

As with all Maxim reference designs, the BOM, schematics, layout files, Gerber filesare all available. In addition, all boards feature through-hole pins for immediate boardplacement and accelerated prototyping, and are available for purchase.