1 System Description

Industrial AC/DC power supplies are used in various applications such as process control, data logging, machinery control, instrumentation, factory automation, and security systems. These AC/DC supplies provide a convenient means for powering DC operated devices including programmable logic controllers (PLCs), sensors, transmitters and receivers, analyzers, motors, actuators, solenoids, relays, and so on. These supplies are convection cooled and need to support features like power boost where it supplies a increased output load for a short duration. The supplies operate over a wide input range from 85- to 265-V AC, delivering full load for entire input voltage range. The output voltages from these supplies range from 5 to 56 V with power ratings from 7.5 to 500 W. Many of these supplies can be connected in parallel for higher power applications.

This reference design is a 500-W high efficiency industrial AC/DC power supply. The design consists of a two-phase-interleaved, critical conduction mode (CrCM) PFC converter, which operates from an input voltage range of 85- to 265-V AC RMS and generates a 400-V DC bus. The second stage is made up of an isolated half-bridge LLC stage, which generates a 24-V, 20-A nominal output. Industrial power supplies have requirements of high efficiency over their entire operating voltage range and wide load variations from a 50% to 100% load. This design demonstrates high efficiency operation in a small form factor (155 × 125 mm) and delivers continuous 480 W of power over the entire input operating voltage range from 85- to 265-V AC. It gives an efficiency of > 94.5% for 230-V AC nominal operation and 92% for 115-V AC nominal operation.

The UCC28064A PFC integrated circuit (IC) controls the interleaved CrCM PFC stage. Interleaved critical conduction mode (CrCM) and continuous conduction mode (CCM) are the two popular topologies for PFC applications with greater than 300-W output power. CrCM PFC has the advantage of minimizing the turnon losses on the PFC MOSFET and eliminates the reverse recovery on the boost diode to reduce losses. CrCM PFC also has a much smaller inductor value than the CCM PFC. The reduced boost inductor value helps to develop the low-profile magnetics necessary for meeting the thin-profile requirement in the design. By interleaving two CrCM power stages, the effective input ripple current is reduced and helps to minimize the EMI filter requirement. The HB-LLC power stage is controlled through the stage of the art UCC256301 resonant controller, which implements current mode control for increased control bandwidth. This increased control bandwidth reduces the output capacitors required to suppress the AC ripple on the output. To achieve high efficiency, the output of the LLC stage uses synchronous rectification based on the UCC24612 device and the CSD19505KCS MOSFET.

The design has low standby power of < 200 mW and meets ENERGY STAR rating requirements as well as 2013 EU eco-design directive ErP Lot 6. The EMI filter is designed to meet EN55011 class-B conducted emission levels. The design is fully tested and validated for various parameters such as regulation, efficiency, EMI signature, output ripple, start-up, and switching stresses. Overall, the design meets the key challenges of industrial power supplies to provide safe and reliable power with all protections built-in, while delivering high performance with low power consumption and low bill-of-material (BoM) cost.