In today’s world of digital information and constant social connection, having a well-designed and efficient data center is essential. These data centers provide the networking, storage, and global connectivity we rely on. Keeping them running smoothly is crucial to avoid data interruptions and corruption. However, older data centers are struggling as they operate near their limits with the market’s increasing demand of computing power, and their usage is continuously increasing rapidly every year. To address these challenges, modern data centers are adopting new designs with higher power density, such as the 48-V architecture, which significantly reduces power losses compared with the traditional 12-V architecture. Intermediate bus converters (IBCs), specifically the quarter-brick (QB) power supply, deliver key benefits when converting high-voltage DC input to lower voltages.

The use of artificial intelligence as a large language model in terms of weekly active users has doubled in less than a year. This has led to a growing need for higher power density, which in turn will need more robust and high-performance power converters.

As data centers scale up to support more powerful servers, networking equipment, and storage systems, they require higher power, which involves several stages of power conversion, from the power transmission line down to the usable DC voltage level inside the rack. The legacy architecture in data centers is converting a rectified AC voltage down to 12 VDC, which will be the main power source inside the motherboards. However, 12-VDC architecture is becoming inefficient for main power delivery within the board. Increasing the input voltage to a 48-V supply allows for up to a 16× reduction in I²R losses across the PCB, with considerably lower conversion losses and within the safety-extra-low-voltage level.

Therefore, an IBC is a critical component in modern data center power architectures: It converts a 48-V voltage bus line from the primary power source, such as an uninterruptible power supply, to the existing intermediate bus voltage (5-V, 12-V architecture) and point-of-load regulators. IBCs come in various power capacities and sizes, including the common QB power supply.

A QB power supply is a compact, efficient type of DC-to-DC converter module that plays a crucial role in modern power systems. It takes a high-voltage DC input and converts it to a lower voltage that is suited for powering a variety of peripherals and core processors inside the motherboard. The term “quarter brick” refers to its small, rectangular shape. These power supplies usually measure about 58.4 × 36.8 mm (2.3 × 1.45 inches) in a PCB area, with a typical height of about 14.5 mm (0.57 inches). Despite the small size, a QB power supply is highly efficient and can be easily integrated into existing power systems.

These power supplies are widely used in data centers, where their compact footprint and high efficiency make them suited for use in server racks, network switches, ventilation systems, rectifiers, and battery backups. Their versatility and reliability make them a go-to solution for meeting the power needs of a modern electronic infrastructure. These power supplies usually operate with input voltage ranges of 40 V to 60 V, although there are variations available for different input voltages. They utilize a switching technique to efficiently regulate and convert the input voltage to a lower, regulated output voltage, typically from 9 V to 16 V. The output voltage can vary depending on the specific requirements.

The key features of QB power supplies include:

• High efficiency: These power supplies are designed to maximize conversion The reduction of conversion losses should be lower than the I²R losses that a legacy 12-VDC architecture will incur.
• High power density: The quarter-brick design can deliver 2 kW on regulated 12.2 V for the same off-the-shelf QB power supply.
• Wide input voltage range: They can accept a broad range of input voltages, making them compatible with various power sources. A typical nominal input voltage range falls within 48 VDC to 54 VDC, with an extended range of 40 VDC to 60 VDC.
• Output voltage regulation: They provide precise and stable output voltage regulation, ensuring consistent performance across different load conditions.
• Protection mechanisms: They incorporate protective features such as overvoltage protection, overcurrent protection, short-circuit protection, and thermal shutdown to safeguard the power supply and the connected
• Thermal management: Efficient heat dissipation is crucial for reliable operation. QB power supplies often include thermal management features such as heat sinks or integrated fans to regulate temperature.
• Remote sensing: Some models support remote sensing, which compensates for voltage drops along the output cables, ensuring accurate voltage regulation at the load.
• PMBus and advanced control features: Many QB power supplies offer advanced control capabilities, such as voltage trimming, remote on/off control, and synchronization with other power modules.
• Scalability: The QB power supply should be easily scalable with minimum circuit adjustment. It can be configured in parallel operation for different power demands and can handle pre-biasing startup for hot-swap capability. Figure 1 shows an example of how each QB power supply can be paralleled.

Figure 1: The quarter-brick power supply can be paralleled by tying the SS and ISHARE pins together. (Source: Analog Devices Inc.)

When selecting a QB power supply, it is essential to consider factors such as input/output voltage requirements, load current, efficiency, operating temperature range, and specific industry certifications or standards applicable to your application. These features are available in a QB reference design, which is suitable for demanding applications that require stable and efficient power delivery.

The key components of a QB power supply include an input filter, an output filter, some feedback control circuitry, and protection mechanisms that may be included in controller or power management ICs. See Figure 2.

Figure 2: ADI’s quarter-brick power supply block diagram (Source: Analog Devices Inc.)

The advantages of QB power supplies include the following:

• Compact size: One of the primary advantages of a QB power supply is its compact form factor, which allows for efficient space utilization in applications in which size is a constraint.
• High power density: Despite their small size, QB power supplies offer high power density, enabling them to deliver significant power outputs.
• Efficiency: With advancements in power conversion technologies, QB power supplies achieve high efficiency levels, reducing energy wastage and minimizing heat dissipation.
• Thermal management: QB power supplies often incorporate thermal management consideration, such as a flat baseplate that can be extended with a heat sink to ensure optimal operation and reliability in challenging thermal environments.
• Reliability and durability: These power supplies are designed to meet stringent industry standards, ensuring long-term reliability and durability even in harsh operating conditions.
• Supply resiliency: QB power supply pins are compatible between different manufacturers due to their common footprint package to ensure a resilient supply chain in production or ease of after-sale support in case of field failures.

Coupled inductors in IBCs

A coupled inductor is another excellent technology to incorporate a QB power supply for intermediate bus applications due to the integer ratio conversion. A 48-V to 12-V conversion will have 50% duty cycle, which makes the buck section operate at a notch for a two-phase coupled inductor design. Even for a wider, 40-V to 60-V (typical) input voltage range, it can still benefit from using a coupled inductor (CL) instead of a discrete inductor (DL). Figure 3 shows the normalized current ripple comparison between a discrete inductor and coupled inductor with different phases.

Figure 3: Normalized current ripple as a function of duty cycle for a given coupling coefficient, Lm/Lk (Source: Analog Devices Inc.)

As seen in Figure 3, the current ripple is minimized at 50% duty cycle for a two-phase coupled inductor design. Notice that the benefit of coupled inductors is not the same across different duty cycles. Different phases have different notch locations where the reduction of current ripple is maximized, so it is important to consider the input voltage range and target output voltage of the QB design. For example, a buck converter with a 4:1 step-down ratio should use a four-phase design to maximize the coupled inductor’s current ripple reduction. See Figure 4 for an example of a single four-phase coupled inductor.

Figure 4: A single four-phase coupled inductor can be used for 48-V to 12-V conversion with a four-phase DC-to-DC converter. (Source: Analog Devices Inc.)

The most important impact of using a coupled inductor in a QB design is its significant reduction in the size of magnetic components, which is required for quarter-brick PCB dimensions. The use of a coupled inductor allows for delivering high output power at competitive efficiency.

Applications of QB power supplies

QB power supplies find applications in various industries and sectors, including telecommunications and industrial automation. They are commonly used in telecom infrastructure, data centers, and networking equipment to power communication systems and network switches and are suited for industrial automation applications such as motor drives, robotics, and control systems.

A QB power supply is suitable for different output voltage step-down ratios. ADI’s discrete quarter-brick reference design, as an example, makes it easier to include multiple coupled inductor footprints to evaluate up to two output voltage levels or parallel them together to test at higher output current requirements. See Figure 5 for the reference design.

Figure 5: ADI’s discrete quarter-brick reference design (Source: Analog Devices Inc.)

Older data centers are struggling to meet the increasing demand for computing power, especially with the rapid growth of AI. To address these challenges, modern data centers are adopting new designs with higher power density, such as the 48-V architecture, which significantly reduces power losses compared with the traditional 12-V architecture. A key component in this transition is the IBC, specifically the QB power supply. These compact, efficient DC-to-DC converters are essential for converting high-voltage DC input to lower voltages required by various peripherals and core processors.

The QB power supplies provide a streamlined, high-performance power solution suitable for diverse applications. Renowned for their compact design, energy efficiency, and robust reliability, these power supplies boast superior power density, accurate voltage regulation, and advanced protective features, making them an essential component across various industries. They are designed to maximize space utilization, ensure reliable operation, and meet the power needs of modern electronic infrastructure.

ADI’s QB power supply delivers key advantages for powering data centers while offering high efficiency, robust performance, and advanced control features. Enhanced reliability and reduced operational costs make it a well-suited solution for efficient and dependable data center power management.

The next part of this series will discuss the comprehensive evaluation of the QB power supply. This will include electrical and thermal performance, as well as the proper component selection for high-power applications.

References

Ben-Yaakov, S., & Evzelman, M. (September 2009). “Generic and unified model of Switched Capacitor Converters.” IEEE Energy Conversion Congress and Exposition, pp. 3501–3508.

Cruz, C. (July 2024). “The Power of 48 V: Relevance, Benefits, and Essentials in System-Level Applications.” Analog Dialogue, 58(3).

Evzelman, M., & Ben-Yaakov, S. (July 2013). “Average-Current-Based Conduction Losses Model of Switched Capacitor Converters.” IEEE Transactions on Power Electronics, Vol. 28, No. 7, pp. 3341–3352.

Haug, B. (February 2018). “72 V Hybrid DC-to-DC Converter Reduces Intermediate Bus Converter Size by up to 50%.” Analog Dialogue, 52(2).

Ikriannikov, A. (March 11, 2015). “The Benefits of the Coupled Inductor Technology.” Analog Devices Inc.

Ikriannikov, A., & Lipcsei, L. (Oct. 27, 2023). “Greatly Increase the Efficiency of the Regulated 48 V to 12 V First Stage.” Analog Devices Inc.

Reuters. (Aug. 29, 2024). “OpenAI says ChatGPT’s weekly users have grown to 200 million.”

Webb, S. & Liu, Y-F. (December 2020). “A novel intermediate bus converter topology for cutting edge data center applications.” Chinese Journal of Electrical Engineering, 6(4), pp. 3–14.

About the authors

Karl Audison Cabas is an applications engineer focusing on power applications at Analog Devices Inc. since September 2020. He holds a bachelor’s degree in electronics engineering from Polytechnic University of the Philippines and a post-graduate diploma in power electronics from Mapua University. He has more than four years of experience in DC-to-DC power converters. His previous function involved catering to customer inquiries and design issues related to DC-to-DC converters. He now works as a power system applications engineer for cloud and data center applications.

Christian Cruz is a staff applications development engineer at Analog Devices Inc. in the Philippines. He holds a bachelor’s degree in electronics engineering from the University of the East in Manila, Philippines. He has more than 12 years of engineering experience in the field of analog and digital design, firmware design, and power electronics, which includes power management IC development as well as AC-to-DC and DC-to-DC power conversion. He joined ADI in 2020 and is currently supporting power management requirements for cloud-based computing and system communications applications.

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