Precautions for power inductor selection

Precautions for selecting power inductors. Power inductors, also known as wound inductors, are electromagnetic induction components made by winding insulated wires such as enameled wire and gauze wrapped wire. Power inductors have strong weather resistance and can be used on computer motherboards, microcontrollers, graphics cards, and other long-term devices. Ordinary power inductors can only be used as DC-DC modules, filtering circuits, etc., which has led to many people's doubts about the selection. Today, we mainly introduce how to select power inductors.

Precautions for power inductance:

1. Frequency

Due to the presence of parasitic capacitors between the coils, which generate parallel resonance with their inductance, there will be a self oscillation frequency (SRF), which is related to EPC. Therefore, the smaller the EPC, the better, ensuring a wider frequency range of inductance. The SRF needs to be at least ten times the switching frequency of the DC-DC transformer, for example, if the switching frequency is 1.2MHz, the SRF needs to be at least 12MHz. Therefore, the power inductor should be hollowed out without any metal, to avoid generating additional EPC and reducing the frequency range of the inductance.

2. Inductance value

In theory, the difference between the maximum and minimum output current, known as the ripple, is expected to be as small as possible, meaning that the output current is more stable. This can result in higher conversion efficiency and lower EMI interference. The larger the inductance value, the smaller the ripple. However, if the inductance value is too large, it will slow down the instantaneous response of the load end, and the output current cannot change synchronously with the exchange cycle in real time. Therefore, it is necessary to select an appropriate inductance value instead of blindly increasing it.

3. Rated current

When the flow current is too large, the inductance value will decrease, and the flow current with a 30% decrease in inductance value is defined as saturation current. At this time, the power inductance that enters the saturation state and enters the saturation state can also be called a power inductance, which is equivalent to a wire and has almost no effect on stabilizing the current. Its ripple will become very large. Therefore, the saturation current is the pointer to determine the linearity of the power inductance, and of course, the larger the better, Generally, it needs to be at least 1.3 times the current flowing through it.

4. Resistance and shielding cover

Every object has its internal resistance DCR, and inductance is no exception. According to P=I * I * R, it consumes a lot of current (which is converted into heat energy), resulting in a decrease in conversion efficiency. Therefore, the smaller the DCR, the better. If the inductance value is too large, it not only slows down the instantaneous response of the load end, but also increases the DCR due to the increase in the number of coils wound. Therefore, it is necessary to select an appropriate resistance value. The power inductor with a shielded cover has a smaller DCR and can prevent EMI, while also avoiding coupling with adjacent metals.

Characteristics of power inductance:

1. Flat bottom surface suitable for surface mounting;

2. Excellent end face strength and good soldering performance;

3. It has the characteristics of high Q value and low impedance;

4. Low magnetic leakage, low direct resistance, and resistance to high currents;

5. Ribbon packaging is available for automated assembly.