GaN-based 4000W totem pole bridgeless PFC realizes high-efficiency server power supply

With the evolution of the power supply industry, the 80 PLUS standard has become more and more stringent. The 80 PLUS program was originally launched by the U.S. Department of Energy and Ecos Consulting is responsible for implementing a nationwide energy saving cash reward program. Initially, in order to reduce energy consumption, system vendors were encouraged to use power supplies with full load, 50% load, and 20% load efficiencies above 80% and a PF value greater than 0.9 under rated load conditions when producing desktops or servers.

A few days ago, Texas Instruments introduced the company’s latest GaN-based 4000W totem pole bridgeless PFC reference design at the TI New Infrastructure semiconductor Technology Forum.

With the evolution of the power supply industry, the 80 PLUS standard has become more and more stringent. The 80 PLUS program was originally launched by the U.S. Department of Energy and Ecos Consulting is responsible for implementing a nationwide energy saving cash reward program. Initially, in order to reduce energy consumption, system vendors were encouraged to use power supplies with full load, 50% load, and 20% load efficiencies above 80% and a PF value greater than 0.9 under rated load conditions when producing desktops or servers.

The program was first implemented in 2003 and was officially included in the Energy Star 4.0 standard specification in 2007. As of today, 80Plus has become one of the most stringent power-saving specifications recognized. The implementation of the 80Plus plan is divided into different phases, which is the so-called “roadmap”. The ultimate goal is to ensure that the conversion efficiency of all power sources reaches more than 90%. But it was not achieved all at once, but gradually increased certification requirements year by year. To this end, in 2008, the 80Plus official organization added three new certifications: Gold, Silver, and Bronze on the basis of the original certification, corresponding to different levels of product certification. Today’s standards include more stringent standards such as platinum and titanium. The half-load efficiency is required to be >96%. The OCP V3 standard requires a peak efficiency of 97.5% and a full load efficiency of 96.5%.

The server power supply mainly includes two parts, namely PFC and DC/DC, which requires both parts to be more efficient.

For traditional PFC, traditional BOOST bridge topology is difficult to further improve efficiency. At present, there are several approaches in the industry, including Active Bridge Rectifier and bridgeless topology. The bridgeless topology includes AC Switch PFC and totem pole PFC. Comparing the three products, the totem pole requires the least number of power devices, the price can be optimized, and the efficiency can also be the highest, and the device uses fewer devices and the design is simpler. Therefore, the totem pole topology will become an important technology for PFC in the future.

GaN-based 4000W totem pole bridgeless PFC realizes high-efficiency server power supply

TI’s 4000W totem pole PFC reference design includes TI’s various devices. Controller, isolation, driver, GaN, differential amplifier, DC/DC, etc. The switching frequency is 50 kHz, and the conversion efficiency reaches 99.1% at 1.5kW.

Using TI’s second-generation GaN products, compared with the first-generation, the size is larger, the support power is higher, and the RDSon is smaller. In addition, TI also has automotive GaN, which uses a top heat dissipation mode, does not require PCB heat dissipation, and has a 650V withstand voltage.

TI’s GaN device encapsulates the driver and FET together, enabling better high-frequency design, achieving a switching speed of 2.2 MHz and a voltage conversion rate of 150V/ns. In addition, a variety of protection functions are integrated inside the chip, including overcurrent, overvoltage, undervoltage, etc., and parameters such as GaN junction temperature can also be reported.

In addition, TI’s products have intelligent dead-time control technology. Because GaN does not have a body diode, the reverse current voltage drop in the third quadrant is large and the loss is large. GaN dead time has a greater impact on efficiency, so TI adopts intelligent dynamic adjustment technology to adjust the dead time according to different cycles. In this way, the loss of about 1W can be reduced.

AC Drop is another important issue. First of all, after one cycle of AC power is restored, the phase-locked loop needs several cycles to recover, which will cause the low-frequency tube to be turned on incorrectly and damage the Power Stage. In order to cope with AC Drop, TI has added a protection function. When AC Drop occurs, C2000 will control to close the low-frequency tube to cut off the circuit as soon as possible. At the same time, it will automatically generate a sine wave as a reference for the phase-locked loop, while waiting for the normal recovery of AC.

TI’s reference design provides all data including testing, so the program also provides EMI and Surge related tests, including thermal management.

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