Recommendations for 5G small base station power supply design

In the 5G era, how to reduce power consumption is an issue that the entire industry chain needs to consider. High efficiency, high power density, and high frequency will be topics that the industry will continue to pay attention to in the future. In Cheng Wentao's view, in terms of efficiency, for communication power supplies, when the power efficiency increases to a certain level, the task of improving efficiency will fall on the radio frequency side. The benefits of a small increase in the efficiency of the radio frequency side will be greater than the efficiency of the power supply part. Improvement; high power density can make the size of equipment smaller, which will be the focus of continued attention of the industry; high frequency needs to rely on new materials to achieve, including silicon carbide, gallium nitride, new magnetic materials, etc., because only active Only when the devices and passive devices are made high-frequency at the same time can the system be made high-frequency.

For power supply design engineers in the 5G era, they must be familiar with new topologies and new materials, because new material devices such as silicon carbide and gallium nitride have not been available for a long time, and the device characteristics introduced by each manufacturer are different. The same thing, unlike silicon device characteristics that everyone is familiar with. Therefore, Cheng Wentao suggested that power supply design engineers should familiarize themselves with new material devices and high-frequency design as early as possible, and develop design ideas to adapt to future power supply design work.

For macro base stations, Infineon's Cheng Wentao gave some suggestions on the optimization of primary and secondary power supplies. "In terms of primary power supply, we see an obvious trend towards high efficiency and high power density. Now the efficiency of power supply must reach 97% or even 98% working efficiency."

To achieve this efficiency goal, Cheng Wentao believes that first, a new topology needs to be used. He gave an example that the topology of ACDC will gradually transition from bridge PFC to bridgeless PFC, and even totem pole topology; second, it must adopt New materials include the currently popular silicon carbide MOSFETs and gallium nitride MOSFETs; the third is high frequency, which can increase power density and reduce size; fourth, patch packaging is more popular, and SMD packaging has become mainstream.

For the secondary power supply part, there are not many new topologies, but more importantly, the use of new materials and high-frequency devices.

Figure: Macro station rectifier in the 5G era

In terms of small base stations, Cheng Wentao believes that small base stations in the 5G era are very different from macro base stations, and are also slightly different from micro base stations and pico base stations in the 4G era. “Nowadays, small base stations are also called distributed base stations by some people. In the 5G era, the radio frequency part and the antenna part will be increasingly integrated together. Unlike in the past, where the RU and the antenna were separated, this compact design has different power requirements."

Figure: Main features of small base station power supply equipment

He believes that there will be the following main changes:

One is the need to use devices with higher voltage levels. If it is to be more compact, the number of acceptable EMI components must be reduced, because EMI components are generally large. However, EMI components are very critical to the radio frequency part. In addition to serving as the electromagnetic compatibility part, they are also responsible for the input part's anti-surge and lightning strike tasks. "This is like a seesaw, how to balance and compact, and still withstand the same or even higher surge and lightning strike pressure after reducing EMI devices." Cheng Wentao also talked about some of the current countermeasures, that is, using withstand voltage levels higher devices.

The second is the need to adopt new packaging forms of devices. Since they need to be made more compact, SMD devices will be used more. And because many small base stations are deployed outdoors, they basically do not use fans. Because fans are expensive to maintain and depreciate quickly, small base stations are now basically fanless designs. So how can we adapt to the changes in outdoor temperature? This requires relying on the shell of the device to help dissipate heat. Cheng Wentao pointed out that many devices now use new packages to help dissipate heat, such as top-layer heat dissipation or double-sided heat dissipation packages.

Third, in the secondary power supply, some new technologies will come out in the DCDC part. "For example, most MOS tubes used to have their drains attached to the PCB, but now many devices are designed with their sources underneath. Source With the pole facing down and using a device with the drain facing down, it has great advantages in terms of EMI, efficiency, PCB layout, etc. when doing synchronous rectification buck." Cheng Wentao said.