MAXREFDES48#: 24V to 12V, 40W isolated power supply with EFD20 core transformer

Overview

Note: This reference design uses an EFD20 core transformer. For a similar reference design using planar transformers, please refer to MAXREFEDES41# .

The MAXREFDES48# reference design (Figure 1) demonstrates the use of the Max17599 's low-IQ, wide-input-range, active-clamp current-mode PWM control. The MAX17599 contains all the control circuitry required for wide-input range, isolated, forward converter industrial power supplies. The reference design operates from an 18V to 36V input voltage range and provides up to 3.5A @ 12V output. The reference design features an active clamp transformer reset structure for forward converters. This reset structure offers numerous advantages, including reduced voltage stress on the switch, reduced transformer size (supporting larger flux swings), and improved efficiency (no lossy snubber circuit required). These features make it a compact, cost-effective isolated power supply . The designed switching frequency is set to 250kHz. For EMI-sensitive applications, the user can set the frequency dithering method to support low-EMI spread spectrum operation.

An input undervoltage lockout (EN/UVLO) is provided to set the power supply startup input voltage (set to 16.5V in the design) to ensure correct operation during brownout conditions. The EN/UVLO input is also used to turn the IC on/off. An overvoltage input (OVI) protection method is provided to ensure that the controller shuts down when the input power exceeds the maximum allowable value (set to 37.0V in the design).

To control inrush current, the device uses the soft-start (SS) pin to set the regulator's soft-start time. Minimizes power consumption under fault conditions through hiccup overcurrent protection (hiccup mode). Soft-stop provides safe discharge of the clamping capacitor when the device shuts down, allowing the controller to restart in a controlled manner.

In addition, a negative current limit feature is provided in the current sense circuit to help limit the clamp switch current under dynamic operating conditions. Overheating fault triggers thermal shutdown to reliably protect the device.

At 24V input, the reference design achieves a maximum efficiency of 92.5% using the supplied components. This versatile power solution can be used in many different types of applications such as programmable logic controllers (PLCs) , industrial process controls , industrial sensors , telecom/datacom power supplies, isolated power chargers, servers , and embedded computing .

System Block Diagram

Figure 1. MAXREFDES48# reference design block diagram.

characteristic

• functional isolation

• Compact and flexible

• Low power consumption

• Minimal number of external components

• Works reliably in harsh industrial environments

application

• PLC

• Industrial process controls and sensors

• Telecommunications and datacom power supplies