egan fet silicon power shoot out volume 10 high frequency resonant converters

Description: Distributed power systems are commonly used in telecommunications, networking, and high-end server applications, utilizing a 48 V bus voltage derived from the telecom industry. This 48 V bus supplies several isolated point-of-load (POL) converters that power the end loads, with isolation necessary for safety. The traditional distributed power architecture (DPA) employs AC/DC front-end converters to deliver the 48 V bus voltage. From this bus voltage, multiple regulated isolated DC/DC POL converters provide the required voltage and power to individual loads. As the complexity of communications, networking, and high-end server systems has increased, so too have the voltage and current demands from a growing number of loads. The presence of numerous regulated 48 V isolated DC/DC POL converters to power these systems leads to significant increases in cost, volume, and complexity. The limitation of the traditional distributed power architecture is that as power demands increase, so does the complexity of the isolated converters required. Fully regulated isolated POL converters tend to be larger, more complex, and more expensive than low-voltage non-isolated POL converters. The isolated converters introduce bulky transformers and complex control systems due to isolation requirements, resulting in lower efficiency and power density. To simplify design, the concept of intermediate bus architecture (IBA) was explored. A prevalent IBA approach uses fewer 48 V isolated bus converters to meet isolation requirements and supply an intermediate bus voltage ranging from 9.6 to 12 V. Final voltage regulation to the loads is provided by smaller, more efficient, regulated non-isolated POL converters, allowing the bus converters to function as unregulated DC/DC transformers, which enhances efficiency and reduces costs. The IBA is widely adopted in many distributed power systems today, demonstrating improved performance and lower overall system costs compared to traditional architectures. The unregulated bus converter, also known as a DCX or DC/DC transformer, typically operates close to a 50% duty cycle to maximize efficiency and power density. Most contemporary bus converters utilize traditional hard-switching bridge topologies operating at lower frequencies to enhance efficiency. At these lower switching frequencies, the isolation transformer and output inductor are quite bulky, occupying substantial board area. To improve power density, increasing the operating frequency can reduce the size of the inductor and transformer. However, as frequency rises in traditional hard-switching topologies, losses from body diode conduction, reverse recovery, and switching increase significantly, which limits the converters' output power capability. To achieve better efficiency at higher switching frequencies, resonant topologies may be employed. Resonant topologies are especially advantageous in DC/DC transformer applications due to the elimination of regulation requirements, allowing the converter to consistently operate at the resonant frequency. This work will examine the advantages of using eGaN FETs in high-frequency intermediate bus converter (IBC) applications. The topology employs a resonant technique utilizing the transformer's magnetizing inductance and the resonance of the leakage inductance, combined with a small output capacitance, to achieve zero voltage switching (ZVS), limit turn-off current, and eliminate body diode conduction. For a direct performance comparison between eGaN FETs and Si MOSFETs in high-frequency resonant bus converter applications, devices with similar on-resistance were selected, maintaining the same circuit topology and layout for both eGaN FET and MOSFET designs.

In a distributed power system, the integration of a 48 V bus voltage facilitates efficient power distribution across various components. The architecture typically begins with an AC/DC front-end converter that rectifies and regulates the incoming AC supply to produce a stable 48 V output. This bus serves as the primary power source for multiple isolated DC/DC POL converters, each tailored to meet specific voltage and current requirements of individual loads. The isolation provided by these converters is crucial for safety and operational integrity, particularly in high-stakes environments like telecommunications and server farms.

As the demand for power increases, traditional architectures face challenges such as increased component size, complexity, and cost. The introduction of the intermediate bus architecture (IBA) addresses these issues by reducing the number of isolated converters needed. Instead of each load requiring a fully isolated converter, the IBA allows for a centralized approach where a smaller number of bus converters provide an intermediate voltage level (9.6-12 V), which can then be efficiently regulated by non-isolated POL converters.

The design of these bus converters is critical for overall system performance. Operating near a 50% duty cycle enhances efficiency, while the use of hard-switching topologies at lower frequencies is common. However, as frequency increases to improve power density, the associated losses become a significant concern. The transition to resonant topologies offers a solution by enabling operation at resonant frequencies, which minimizes losses and enhances efficiency.

The application of eGaN FETs in this context represents a significant advancement, as these devices are designed to perform effectively at higher frequencies, improving the overall performance of the IBC. The resonant technique employed in the design leverages the transformer's inherent properties to achieve zero voltage switching, which is essential for reducing switching losses and improving thermal management within the system. This comprehensive approach to power distribution not only enhances efficiency but also reduces the overall footprint and complexity of the system, making it a viable solution for modern high-demand applications.Distributed power systems are prevalent in telecommunications, networking, and high-end server applications and utilize a 48 V bus voltage adopted from the telecom industry. From the 48 V bus, a number of isolated point of load (POL) converters power the end loads, with isolation being required for safety.

The traditional distributed power archite cture (DPA), Fig. 1(a), uses AC/DC front end converters to deliver the 48 V bus voltage. From the 48 V bus voltage, a number of regulated isolated DC/DC POL converters are used to deliver the required voltage and power to the individual loads. As communications, networking, and high-end server systems have become more complex, the voltages and currents demanded by the growing number of loads have increased significantly [1].

Having a large number of regulated 48 V isolated DC/DC POL converters to power these systems significantly increases the cost, volume, and complexity of the system. The limitation of the traditional distributed power architecture is that as the power demands of the loads increased so did the complexity of the isolated converters required.

Fully regulated isolated POL converters are much larger, more complex, and more expensive than low voltage non-isolated POL converters. The isolated converters introduce a bulky transformer and complex control due to the isolation requirements; this leads to lower efficiency and power density.

To simplify design, the concept of intermediate bus architecture (IBA) was considered[2] [3]. A popular IBA approach, shown in Fig. 1(b), employs a lower number of 48 V isolated bus converters that satisfy isolation requirements and supply an intermediate bus voltage ranging from 9. 6-12 V. With the final regulation to the loads provided by smaller, more efficient, regulated non-isolated POL converters, the bus converters can be operated as unregulated DC/DC transformers, improving efficiency and reducing cost.

The IBA is widely used in many distributed power systems today, yielding improved performance and lower overall system cost when compared to traditional architectures. The unregulated bus converter, also known as a DCX, or DC/DC transformer, is generally operated close to 50% duty cycle to offer the highest efficiency and power density.

The majority of today`s bus converters use traditional hard switching bridge topologies operating at lower frequencies to maximize efficiency. At lower switching frequencies, the isolation transformer and output inductor are very bulky, occupying a large portion of the board area.

In an effort to improve power density, the operating frequency can be increased to shrink the inductor and transformer size [4]. As frequency is increased in traditional hard switching topologies, the losses from body diode conduction, reverse recovery, and switching increase significantly, limiting the converters output power capability.

To offer improved efficiency at higher switching frequencies, resonant topologies may be considered. Resonant topologies[5]-[8] are particularly beneficial in DC/DC transformer applications, due to the removal of the regulation requirement, allowing the converter to always operate at the resonant frequency. For this work, the benefits of the eGaN FET applied in a high frequency intermediate bus converter (IBC) will be considered.

The topology, shown in Fig. 2, employs a resonant technique that utilizes the transformer`s magnetizing inductance (LM) and resonance of the leakage inductance (LK), with a small output capacitance (CO), to achieve zero voltage switching (ZVS), limit turn off current, and eliminate body diode conduction [5]. To obtain a direct comparison in performance between eGaN FETs and Si MOSFETs in the high frequency resonant bus converter application, devices with similar on-resistance were selected, the same circuit topology was used, and a similar layout was maintained for the eGaN FET and MOSFET designs.

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