Sendust（ Fe-Si-Al）Ring Filter Inductor:* Core features: It can be regarded as an "upgraded version" of the iron powder core. Made of iron, silicon, and aluminum powders.Its magnetostriction coefficient is close to zero, so it is not prone to generating noise.
* Advantages: The loss is lower than that of the iron powder core, and the efficiency is higher. It also has a distributed air gap and good anti-saturation performance. It has no audio noise and is suitable for noise-sensitive applications. It has good temperature stability.
* Disadvantages: The cost is slightly higher than that of the iron powder core, and the saturation magnetic flux density is slightly lower.
* Typical applications: Common colors:
Performance of Iron Silicon Aluminum (Sendust) Powder Cores in Filter Inductors Iron Silicon Aluminum (Sendust) powder cores are formed by insulating, compressing, and heat-treating alloy powder consisting of 85% iron, 9% silicon, and 6% aluminum. It is a balanced and excellent magnetic powder core material. Detailed Core Performance Characteristics 1. Excellent Anti-DC Bias Capability (Anti-Saturation)
Mechanism: The essence lies in its distributed air gaps. Countless tiny insulated particles form numerous microscopic air gaps, giving the magnetic path high resistance to saturation.
Performance: The inductance value (L) decreases gradually with increasing DC current (Idc). This means:
At the designed rated current, the inductance does not experience a "cliff-like" drop, leading to safer and more stable system operation.
Even under momentary current overload, the inductor can still maintain some functionality, enhancing system robustness.
Comparison: Its anti-saturation capability is superior to that of Mn-Zn ferrites (except for those with large air gaps intentionally added), but its saturation flux density (Bsat ~ 1.05T) is slightly lower than that of iron powder cores (~1.4T) or high-flux powder cores (~1.5T).
2. Low and Stable High-Frequency Losses
Low Core Loss: Sendust material has high resistivity, and the insulated powder effectively suppresses eddy currents. Its total core loss (iron loss) over a wide frequency range is significantly lower than that of iron powder cores of the same specification, especially in the mid-to-high frequency range (tens of kHz to hundreds of kHz).
Good Temperature Stability: Its losses change relatively gradually with temperature, avoiding the sharp increase in loss at specific temperature points seen in some materials. This makes thermal management more predictable.
Result: Under the same operating conditions, Sendust inductors have lower temperature rise and higher overall efficiency, making them particularly suitable for switch-mode power supplies pursuing high efficiency.
3. Near-Zero Magnetostriction Effect This is the standout feature of Sendust. Magnetostriction refers to the slight deformation of the core during magnetization.
Advantages:
No Acoustic Noise: When the operating frequency or its harmonics fall within the audible range (20Hz-20kHz), the inductor does not produce a "buzzing" sound due to core vibration. This is crucial for consumer electronics (e.g., TVs, audio systems, adapters).
Low EMI Radiation: Reduces additional electromagnetic interference caused by mechanical vibration.
4. Good Temperature Stability and Long Service Life
Low Permeability Temperature Coefficient: Over a wide temperature range from -55°C to +125°C, the rate of change in its inductance is small, typically better than that of iron powder cores. This means more consistent circuit performance across different environments.
Stable Physicochemical Properties: The alloy material is oxidation-resistant, corrosion-resistant, and not prone to degradation from prolonged high temperatures or humidity, resulting in a long service life and high reliability.
Key Electrical Parameter Analysis (Taking typical -60μ/-75μ material as an example) Parameter | Interpretation | Impact on Design | Initial Permeability (μi) | Common specifications include 26μ, 60μ, 75μ, 90μ, etc. This value、 represents the inductance factor (AL value) without DC bias. | A higher μ value yields greater inductance for the same core size and number of turns, but it relatively weakens the anti-DC bias capability. A trade-off based on operating current is needed. | Saturation Flux Density (Bsat) | Approximately 1.05 T (25°C). Bsat decreases as temperature rises. | Determines the maximum Ampere Turns (magnetomotive force) the core can handle. It is the core basis for calculating the required core size and turns to prevent saturation. | Core Loss | Manufacturers provide loss curves (unit: mW/cm³) for different frequencies (f) and flux density swings (ΔB). | This is key for calculating efficiency and high-frequency temperature rise. The low-loss characteristic of Sendust directly translates to lower operating temperatures and higher efficiency. | DC Bias Characteristic | Manufacturers provide curves of "Inductance Attenuation vs. DC Magnetic Field Strength (Oe) or DC Current (A)". | Core to design. It must be ensured that the attenuated inductance value (L(I)) at the maximum operating DC current (Idc_max) still meets circuit requirements for ripple suppression or energy storage. |
Typical Application Scenarios (Why Choose It?)
Output Filter Chokes in Switch-Mode Power Supplies: Need to handle large DC current + high-frequency ripple current. The low loss and anti-saturation properties of Sendust are a perfect match.
Energy Storage Inductors in DC-DC Converters (Buck, Boost):
Buck Circuits: In Continuous Conduction Mode, the inductor carries continuous DC. The gentle saturation characteristic of Sendust is key.
Boost/PFC Inductors: Operate in Continuous or Critical Mode, with high current stress and high ripple frequency. The low loss and high efficiency of Sendust are crucial.
Input Differential Mode Filter Inductors: Need to withstand pulsating DC from the rectifier bridge while suppressing differential mode noise. The overall performance of Sendust is superior to iron powder cores.
Noise-Sensitive Equipment: Such as power supply sections of LCD TVs, high-end audio equipment, and medical devices, where its "noise-free" characteristic is mandatory.
Industrial & Communication Power Supplies Requiring High Efficiency and High Reliability: Its stable temperature characteristics and long service life are highly favored.
Comparison with Main Competing Products Characteristic | Sendust Powder Core | Iron Powder Core | Gapped Mn-Zn Ferrite | Anti-Saturation Capability | Strong (Gentle) | Very Strong (Most Gentle) | Medium (Depends on gap design) | High-Frequency Loss | Low | High | Very Low | Cost | Medium | Lowest | Low to Medium | Acoustic Noise | None | Possible | Likely | Temperature Stability | Good | Fair | Good | Optimum Frequency Range | ~50kHz ~ 500kHz | ~50kHz ~ 200kHz | >100kHz (up to MHz range) |
Key Points for Selection and Design
Calculate the required inductance (L) and maximum DC current (Idc_max).
Select the permeability (μ): Choose higher μ (e.g., 75μ/90μ) when current is low but large inductance is needed; choose lower μ (e.g., 26μ/60μ) when current is large to achieve better DC bias characteristics.
Consult the manufacturer's DC bias curves: Confirm that the inductance attenuation for the selected core size and number of turns at Idc_max is acceptable (typically requiring attenuation not to exceed 20%-30% of the initial value).
Consult the core loss curves: Calculate ΔB based on operating frequency and ripple current, estimate core loss and temperature rise, ensuring they are within safe limits.
Check the winding window area: Ensure the selected wire gauge can be wound within the window and that the copper loss is acceptable.
Core Characteristics of Single-Wire Filter Inductors Using Iron Silicon Aluminum (Sendust) Powder Cores I. Electrical Performance Characteristics
Excellent DC Bias Stability (Anti-Saturation)
Fundamental Reason: The "distributed air gap" structure formed by pressing insulated alloy powder.
Performance: The inductance value (L) decreases smoothly and predictably with increasing DC current (Idc), with no abrupt changes. This makes circuit design safer, as the inductor maintains a certain level of functionality even under transient overcurrent conditions.
Superior High-Frequency Low-Loss Characteristics
The high resistivity of the Sendust material itself, combined with the insulating layers between powder particles, effectively suppresses high-frequency eddy current losses.
Result: Within the commonly used switching frequency range of tens of kHz to hundreds of kHz, its core loss is significantly lower than that of traditional iron powder cores, leading to higher operational efficiency and lower self-heating.
Outstanding Temperature and Frequency Stability
The variation of inductance with temperature and frequency is relatively small. Across a wide temperature range from -55°C to +125°C, its performance parameters (such as permeability, loss) change gradually, ensuring consistent circuit operation under different environmental conditions.
II. Physical and Reliability Characteristics
Iron Silicon Aluminum (Sendust) inductors are primarily used in current paths where "DC (or low-frequency AC) is superimposed with high-frequency ripple," serving functions such as energy storage, current smoothing, and differential mode noise suppression. Their applications span various levels, from consumer electronics to industrial equipment. I. Switch-Mode Power Supplies (SMPS) – The Mainstream Application Field This is the most common and classic application area for Sendust inductors. II. DC-DC Converters and Voltage Regulator Modules III. Fields with Stringent Noise and Reliability Requirements IV. New Energy and Green Energy |
