Use a fixed ratio converter to improve the efficiency of the power supply network

Most electromechanical loads or semiconductor loads require stable DC-DC voltage conversion and strict voltage stabilization for reliable operation. DC-DC converters that perform this function are usually called point-of-load (PoL) regulators. They are designed with maximum input voltage and minimum input voltage specifications, and their specifications define their stable operating range. The complexity of the power supply network (PDN) of these regulators may vary depending on the number and type of loads, overall system architecture, load power level, voltage level (conversion level), and isolation and voltage regulation requirements.

Most electromechanical loads or semiconductor loads require stable DC-DC voltage conversion and strict voltage stabilization for reliable operation. DC-DC converters that perform this function are usually called point-of-load (PoL) regulators. They are designed with maximum input voltage and minimum input voltage specifications, and their specifications define their stable operating range. The complexity of the power supply network (PDN) of these regulators may vary depending on the number and type of loads, overall system architecture, load power level, voltage level (conversion level), and isolation and voltage regulation requirements.

Many power system designers regard the regulated DC-DC converter as the key to the overall design. However, to provide a suitable voltage to the point-of-load regulator, PDN regulation is not necessarily required, or PDN regulation is not so important for the intermediate distribution bus voltage. When considering this point, power system engineers should consider applying a fixed ratio DC-DC converter, which can significantly improve the overall performance of the PDN.

How to optimize the power supply network

PDN performance is usually measured by power consumption, transient response, physical size, weight, and cost. A major design challenge that affects PDN performance is the ratio of voltage conversion and high-precision line/load regulation. Engineers spend a lot of time dealing with a large number of different input/output voltage conversion rates, dynamic adjustment rates and distribution characteristics to improve performance and reliability.

If the system load power consumption is in the kilowatt range, the high-voltage design and large-capacity PDN can reduce the current level in the system (P=V•I), so the PDN size can be reduced, weight and cost can be reduced (cables, busbars) Platoon, motherboard copper foil power layer) (PLOSS = I2R). Before converting to low voltage/high current, it is a big advantage to maximize the high voltage operation time and get as close to the load as possible.

But to make the high-voltage, high-power PDN close to the load, a DC-DC converter with high efficiency and high power density is required. If the input to output voltage conversion ratio is large, such as 800V or 400V to 48V, the most efficient converter is a fixed-rate converter that provides unregulated voltage. These high-efficiency converters not only provide higher power density, but also provide more convenient thermal management due to lower power consumption.

What is a fixed ratio converter?

The working principle of a fixed ratio converter is similar to that of a transformer, but instead of AC-AC conversion, it performs DC-DC conversion. The output voltage is a fixed ratio of the DC input voltage. Like the transformer, this converter does not provide output voltage regulation, and the input to output transformation is determined by the “turn ratio” of the device. This turns ratio is called the K factor, which is expressed as a fraction relative to its voltage drop capability. The K factor ranges from K=1 to K=1/72, and can be selected according to the PDN architecture and PoL regulator design specifications.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure A: The working principle of a bidirectional fixed ratio converter. The buck converter with K=1/16 can also be used as a boost converter with K=16/1.

Typical PDN voltages are low voltage (LV), high voltage (HV) and ultra high voltage (UHV).

Fixed ratio converter voltage category

LV

48V, 28V or 24V

HV

380V, 270V

UHV

800V, 600V, 540V

Fixed-ratio converters can be isolated or not, and can achieve bidirectional power flow through reverse voltage conversion. For example, a K=1/16 fixed ratio converter that supports bidirectional function can be used as a K=16/1 boost converter.

Additional design flexibility includes easy parallel connection (which can meet the power requirements of higher power) and the option of series converter output (which can effectively change the K factor to provide higher output voltage) and so on.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure B: BCM converters are easy to connect in parallel to meet higher power requirements.

The power demand of many end markets and applications has risen sharply, so the power supply network is undergoing major changes. Due to the addition of new features and the continuous improvement of performance levels, higher PDN voltages (such as 48V) are being used in electric vehicles, light-duty hybrid vehicles, and plug-in hybrid vehicles. 48V meets the safety electrical low voltage (SELV) standard required by many systems, and P=V•I and PLOSS=I2The simple power equation of R also explains why the high-voltage PDN is more efficient.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure C: The BCM with the output connected in series to increase the output voltage can achieve higher design flexibility.

For a given power level, compared with a 12V system, the 48V system current is 1/4 and the line power consumption is 1/16 lower. At 1/4 of the current, cables and connectors can be smaller, lighter, and cost less. The 48V battery used in hybrid vehicles has four times the power of 12V batteries. The increased power supply can be used in power system applications to reduce carbon dioxide emissions, increase fuel mileage and add new safety and entertainment features.

The addition of artificial intelligence (AI) to the data center racks has increased the rack power requirements to more than 20kW, so the use of 12V PDN is bulky and inefficient. Using 48V PDN, you can get the same advantages as hybrid cars. In automotive and data center applications, it is best to keep the original 12V load and POL commonly used buck regulators to minimize the need to modify the content.

Use non-isolated fixed ratio converters to solve practical problems

48V complies with the SELV standard, so the non-isolated fixed ratio converter is ideal for the 48V to 12V DC-DC conversion stage, because the current PoL 12V regulator can cope with changes in the input voltage. The non-isolated, non-regulated fixed ratio converter is the most efficient high-power bus converter, which can achieve lower power consumption, higher power density and lower cost. This high density facilitates the use of the latest distributed power distribution architecture in hybrid vehicles, where non-isolated fixed-ratio converters can be placed next to the load, so that a smaller, more efficient 48V PDN can be run around the car to the maximum. In blade servers, this small non-isolated 48V to 12V fixed ratio converter can be placed on the motherboard close to the buck regulator.

Many new AI accelerator cards (such as NVidia’s SXM and Open Computing Project (OCP) member OAM cards) are designed with 48V input because the AI ​​processor power level is between 500 and 750W. For cloud computing and server companies that still use 12V PDN backplanes in their racks to use these high-performance cards, they need to convert from 12V to 48V. Add a bidirectional K=1/4 non-isolated fixed ratio converter to these accelerator cards (or in higher power distributed 12V to 48V modules) as a 12V to 48V boost converter (K ​​= 4/1 ), the AI ​​function can be easily brought into the old rack system.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure D: The 48V power supply of the original system

Vicor NBM2317 can efficiently convert 48V to 12V, and can also convert 12V to 48V, because NBM is a bidirectional converter. The bidirectionality can integrate the original circuit board into the 48V infrastructure, and the latest GPU can also be integrated into the original 12V rack.

How to meet the requirements of demanding high-voltage applications that require isolation

electric car

In electric vehicle applications, power requirements determine that the battery voltage must be much higher than the 48V currently used in hybrid vehicles, usually 400V. 400V is converted to 48V and distributed to different loads around the powertrain and chassis. To support fast charging, the 400V battery is charged by an 800V to 400V converter from a charging station that provides a regulated 800V DC output.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure E: The distributed 48V architecture places multiple smaller converters with lower power consumption close to the 12V load.

In 400V/48V and 800V/400V applications, due to the high power requirements, isolated K: 1/8 (400/48) and K: 1/2 ( 800/400) Parallel array of fixed ratio converters. Voltage regulation can be provided before or after the fixed ratio converter stage. The unregulated power density and efficiency gains are not only effective at this location in this extremely high power application, but also simplify thermal management.

High performance computing

High performance computing (HPC) system rack power level is usually higher than 100kW, so use 380VDC As the main PDN. In these applications, K: 1/8 and K: 1/16 isolated fixed ratio converters are integrated in server blades or on mezzanine cards that distribute power through the rack to provide 48V or 12V power to the motherboard. The voltage regulation is then provided by a 12V multiphase buck converter array or a higher-efficiency advanced 48V to POL architecture. The density and efficiency of fixed-ratio converters once again play an important role in the realization of this type of PDN architecture, which can achieve high performance.

Tethered drone

Another high-voltage application that requires isolation is tethered drones. The length of the power cord of a tethered drone may exceed 400 meters, and the drone must lift and hold it to reach its flying height. The use of high voltages such as 800V can significantly reduce the size, weight and cost of these bulky power cords, thereby enabling higher performance drones. Use the onboard fixed ratio converter (generally K=1/16) to convert to 48V, which can provide a very efficient and extremely small power supply solution to fully meet the needs of airborne Electronic products and video payloads.

Use a fixed ratio converter to improve the efficiency of the power supply network

Figure F: The higher the voltage, the lighter the wire, and the higher the tethered drone will fly.

5G communication

Now, the world is upgrading the latest 5G system with 4G radios and antenna towers 5 times the previous 4G equipment. The 4G PDN is 48V and is provided from the ground power system through a cable. With the addition of 5G equipment, the power level is significantly improved. If the PDN is to be maintained at a voltage of 48V, the diameter will be very large and the wires will be heavy. Telecom companies are studying the use of 380VDC The advantages of PDN to significantly reduce the size of the cable. Using the bidirectional K 1/8 fixed ratio converter in boost mode, the ground 48V power system can provide 380V power to the top of the tower (K: 8/1). 4G and 5G systems use a 380V to 48V regulated converter on the top of the tower, which not only can obtain a 48V regulated power supply, but also can achieve a lower cost power supply through a 380V thin wire.

Fixed-ratio converters provide highly flexible PDN designs for high-performance applications

The demand for high-performance power supplies continues to rise. Enterprise and high-performance computing advanced systems, communications and network infrastructure, autonomous vehicles, and a large number of transportation applications are just a few of the high-growth industries that require more power. These markets have a common feature: each market has a huge power demand, they can all benefit from high power density small DC-DC converter solutions, saving space and reducing weight. Power system engineers should regard fixed-ratio converters as an important and highly flexible solution for achieving higher performance PDNs in order to gain a competitive advantage in overall system performance.

Author Phil Davies, Vice President of Global Sales and Marketing, Vicor

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