Q：Calculation Example of Inductance

A：Electrical specifications:
Core:NPF157060
AL :81 nH/N²
TNumbers of turns: 75T
Current: DC 15A
Initial sensitivity (@ 0A):
L@0A=ALN2=81*752/1000=455.6（μH）
The magnetic field strength at a current of 15A is:
H=0.4πNI/Le=0.4*3.14*75*15/9.84=143.6（Oe）
According to the NPF60 μ DC bias curve, when the magnetic field strength is 143.6 Oe, the magnetic permeability is 54% of the initial permeability. So, the inductance at 15A is:
L（@15A）=455.6x0.54=246（μH）

Q：Curie temperature of inductive magnetic core

A：In the field of electronic engineering, transformers and inductors are indispensable components that play a crucial role in regulating current and voltage in circuits. However, the performance of these components is not unlimited, and one important influencing factor is the Curie temperature of the magnetic core material.
The definition and importance of Curie temperature
The Curie temperature, also known as the Curie point or magnetic transition point, refers to a specific temperature at which the magnetic field strength of a magnetic material drops to zero. This phenomenon was first discovered by the Curie couple in the late 19th century, who observed that when a magnet is heated to a certain temperature, its magnetism disappears. For transformers and inductors, if the temperature of the magnetic core exceeds the Curie temperature, it will cause the inductance to drop to zero, resulting in direct failure or even burnout.
Curie temperature of power manganese zinc ferrite
Power manganese zinc ferrite is a commonly used magnetic core material with a Curie temperature above 210 ℃. This means that in most cases, the insulation materials of transformers and inductors have a temperature resistance level lower than this temperature, ensuring that the magnetic core does not reach the Curie temperature. However, in design and selection, we still need to reserve sufficient margin to ensure that the temperature of the magnetic core is always below the Curie temperature.
The challenge of high conductivity manganese zinc ferrite
Compared with power manganese zinc ferrite, high conductivity manganese zinc ferrite has a lower Curie temperature, approximately above 110 ℃. This requires us to pay more attention to the operating temperature of the magnetic core during design to avoid exceeding the Curie temperature. The insulation materials of most transformers and inductors have a temperature resistance level higher than this temperature, but the temperature of the magnetic core can easily exceed the Curie temperature during operation, so special attention needs to be paid to the design of high conductivity magnetic cores.
Application considerations of nickel zinc ferrite
The Curie temperature of nickel zinc ferrite is above 100 ℃, similar to high conductivity ferrite. We need to focus on the temperature of the magnetic core during the operation of transformers and inductors to ensure that it does not exceed the Curie temperature. This is particularly important for our commonly used nickel zinc products, such as I-shaped inductors, rod inductors, and nickel zinc ring inductors.
High temperature resistance of alloy powder core
The Curie temperature of alloy powder cores is relatively high, usually above 450 ℃. In this case, we need to pay more attention to the temperature resistance level of other constituent materials of transformers and inductors to ensure the stability and safety of the overall components.
In the design and selection of transformers and inductors, it is crucial to consider the Curie temperature of the magnetic core material. By reserving sufficient temperature margin, it is possible to ensure that the magnetic core material operates at a safe temperature.

Q：How to determine if the inductor core is saturated?

A：In the field of power electronics, the performance of inductors is crucial. How to determine whether the inductor core has reached saturation state is crucial for ensuring the stability and efficiency of the inductor.
1、 The concept of saturation current
Saturation current refers to the current value in the winding when the inductor core reaches saturation state. Beyond this current value, the inductance will completely enter saturation state, causing a rapid decrease in inductance.
2、 Measurement of magnetic flux density
Another method to evaluate the saturation level of an inductor core is to measure the magnetic flux density. The magnetic flux density B is the ratio of the magnetic flux Φ to the effective cross-sectional area A of the magnetic core. Magnetic flux can be measured using a magnetometer or Gaussian meter, and magnetic flux density can be calculated based on this. If the magnetic flux density of the inductor exceeds the saturation magnetic flux density Bs of the magnetic core material, it indicates that the magnetic core is saturated.
3、 The influence of temperature on magnetic flux density
The saturation magnetic flux density of the magnetic core varies at different temperatures. At 25 ℃ and 100 ℃, the saturation magnetic flux density of the magnetic core will change. Therefore, when determining whether the magnetic core is saturated, temperature factors must be taken into account.
4、 Overvoltage and overcurrent testing
In the overall power testing, we usually conduct 120% overvoltage and overcurrent point tests. Observe whether there is distortion or abnormal oscillation in the output voltage waveform of the power supply under these extreme states to evaluate the performance of the inductor.
5、 Load testing
By conducting load tests on inductors, applying different loads, and observing changes in parameters such as voltage, current, and power, we can evaluate the saturation level of the inductor core.
6、 Observation of operating status
Observing the operating status of an inductor during operation is also an effective method to determine whether the magnetic core is saturated. If there is abnormal temperature rise, sound or vibration in the inductor, it may be caused by magnetic core saturation.
The saturation state of an inductor core has a direct impact on its performance. Through the above methods, we can effectively determine whether the inductor core is saturated and take corresponding measures to optimize its performance.