Server power supplies need to deliver stable power while operating efficiently under demanding load conditions. As server processors and accelerators require more power, the magnetic components inside the power supply have become increasingly important.
Transformers, inductors and common mode chokes perform different functions throughout the power conversion system. Their design affects efficiency, thermal performance, power density and electromagnetic compatibility.
Transformers are commonly used in isolated power conversion stages.
A transformer transfers energy between the primary and secondary sides while providing electrical isolation. Its turns ratio can also be used to achieve the required voltage conversion.
The transformer core, winding structure, operating frequency and insulation system all affect the performance of the power supply.
For high-power server applications, the transformer needs to handle high switching frequencies and significant power while keeping core and winding losses under control.
Power inductors are widely used in the output and DC-DC conversion stages of server power supplies.
They store magnetic energy and help control current ripple. In a switching converter, the inductor is an important part of the voltage regulation process.
Server power supplies may require inductors capable of handling high current while maintaining low DC resistance and acceptable temperature rise.
As processor power continues to increase, high-current and high-power-density inductors become increasingly important.
Common mode chokes are mainly used for EMI filtering.
They are designed to suppress common mode noise while allowing the desired differential current to pass through the circuit.
In server power supplies, common mode chokes may be used on the input side to help control conducted electromagnetic interference.
The core material, winding structure, rated current and impedance characteristics all affect filtering performance.
Differential mode inductors can also be used in input or output filtering circuits.
Unlike a common mode choke, a differential mode inductor is designed to impede unwanted differential-mode current.
The appropriate magnetic component depends on the type of noise that needs to be controlled.
In some power supply designs, common mode and differential mode filtering are used together.
Power factor correction circuits are commonly found in AC-input server power supplies.
A PFC inductor is an important magnetic component in the PFC stage. It stores energy and helps shape the input current waveform.
Because the PFC stage may operate at relatively high power, the inductor needs to handle substantial current while keeping core and copper losses under control.
Core material, inductance, saturation current and temperature rise are important selection factors.
High frequency transformers are used in switching power conversion stages.
Operating at a higher frequency allows the magnetic components to be smaller than traditional low-frequency transformers for a comparable power level.
However, high frequency operation also introduces core and winding losses that need to be managed carefully.
The winding structure may need to address skin effect and proximity effect, particularly at high switching frequencies.
Output inductors are used to smooth the current delivered to the load.
They work together with capacitors and the switching circuit to reduce output ripple and maintain stable DC power.
For server applications, the output inductor may need to handle high continuous current and rapid changes in load.
Low DCR and good thermal performance can therefore be important.
Modern server processors and accelerators can create substantial changes in power demand.
The magnetic components used in the power supply need to handle high current without excessive saturation or heating.
For this reason, high-current inductors may use larger magnetic cores, thicker conductors, multiple parallel wires or copper foil winding structures.
The exact design depends on the power supply topology and operating frequency.
Magnetic components directly affect several important characteristics of a server power supply.
These include:
Power conversion efficiency
Power density
Temperature rise
Current ripple
Voltage regulation
EMI performance
Reliability
A poorly designed transformer or inductor can increase losses and heat, limiting the performance of the complete power supply.
The selection process should start with the actual electrical requirements.
Important specifications can include operating frequency, voltage, current, power level, inductance, saturation current, DCR and temperature range.
The physical dimensions and cooling conditions also need to be considered because server power supplies typically have strict space and thermal constraints.
For high-power applications, magnetic components should be evaluated under realistic load conditions rather than relying only on nominal datasheet values.
Standard magnetic components may not always provide the required combination of current capacity, efficiency, size and thermal performance.
Custom transformers and inductors can be designed around the power supply topology and mechanical limitations.
The manufacturer may adjust the core material, winding structure, conductor size, air gap and insulation system to meet specific requirements.
This can be particularly useful when designing high-density server power supplies.
When sourcing magnetic components for server power supplies, consider the manufacturer's experience with high-frequency and high-current applications.
Check its core materials, winding capabilities, testing equipment, production capacity and quality control.
For customized transformers or inductors, engineering support is also important because the magnetic component needs to work together with the complete power conversion circuit.
The main magnetic components used in server power supplies include power transformers, high frequency transformers, power inductors, PFC inductors, output inductors, common mode chokes and differential mode inductors.
Each component performs a different role, but they work together to achieve efficient power conversion, current control, filtering and EMI reduction.
As server power requirements continue to increase, magnetic component design will remain an important part of improving power density, efficiency and reliability.
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