Power

Inductors for the Lowest Power Losses in a High-Current Point-of-Load Application

12 September 2018

Today, the trend of electronic equipment and devices is focused on smart designs that are small, thin and lightweight. These trends challenge design engineers to provide high power conversion efficiency, high power density and high reliability, plus environmental protection with an optimal cost-performance ratio. Due to the rapid progress in materials, process technology and computer-aided design tools, design engineers can create new products more rapidly than ever before. ITG Electronics Inc. (ITG) offers a wide range of standard magnetic products to the power conversion market. ITG also has an extraordinary level of expertise in both designing and manufacturing custom magnetic components and EMI filter solutions for its customers worldwide.

Contents

A highly efficient and stable power supply is extremely important to electronic equipment and devices that in general contain multiple sets of point-of-load (POL) power circuits such as the 5.0 V and the 3.3 V supply systems on a motherboard. As a result, the first consideration for a design is how to choose a power inductor for a POL application that meets the high-efficiency requirements. The following is an example for reference: an input voltage of 12 V, output voltage of 5.0 V and output current of 26 A.

Step 1. Circuit Design Topology

Since, as stated, the input voltage is 12 V, the output voltage is 5.0 V and the output current is 26 A, the design calls for a single-phase synchronous rectified buck converter topology.

Step 2. Circuit Switching Frequency Design

According to printed circuit board (PCB) space requirements along with power conversion efficiency and power density, the commonly designed switching frequency is chosen in hundreds of kilohertz (KHz). The following example is at 500 KHz.

Step 3. Circuit Parameter Calculation

Figure 1: Duty cycle schematic diagram.

1. Duty cycle: D=Vout/Vin; D= 5.0 V / 12.0 V = 0.417
2. Ripple current, delta IL: about 20% to 30% of output current is generally selected. The following example uses delta IL(pk-pk) = 0.30 x Iout
3. 30% of Iout is selected for delta IL(pk-pk). delta IL(pk-pk) = 0.30 x 26 A = 7.8 A

The current waveform of the inductor is shown in the figure below:

Figure 2: Schematic diagram of inductor ripple current. Step 4. Calculate the Inductance Value by Using the Engineering Tool at the ITG Web Site.

ITG offers a free tool for inductor calculation for buck and boost converter applications. Simply enter the circuit design parameters, preferred inductor size and DC resistance value and then press the Calculate button. The inductance (L) and other parameter values will be calculated and shown as below.

Figure 3a: Buck converter design tool’s entry page from ITG’s website.

Figure 3b: Calculation result page of buck converter design tool from ITG’s website.

Clicking on the Recommended ITG P/N button will show the inductors that best meet the parameters.

Figure 3c: Screen of recommended ITG P/N.

Review additional technical information by clicking through the part number hyperlink as shown in Figure 3d and 3e.

Figure 3d: ITG web site screen shot of inductor series description.

Access the product series data sheet by clicking on the Data Sheet button.

Figure 3e: ITG website screen shot of an inductor datasheet.

Step 5. Inductor Core Material Selection

Ferrite, iron powder and alloy powder are the most commonly adopted soft magnetic core materials for power inductors. Below are three different types of inductors using different core materials in a very similar 13 by 14 mm footprint for a comparison study.

They are:

1. SLM534214A-1R0MHF: ferrite core and clip wire
2. SC5026-1R0MU: 200° C-rated iron powder core and flat wire
3. SMHC5026-1R0MHF: alloy powder core and round wire

Figure 4: Comparison table of inductor parameters.

The power efficiency and thermal performance of the three inductors in the same power supply board of a single-phase synchronous rectified buck converter are compared with the same test equipment and environmental and test conditions. The comparison results are shown in Figure 5 and Figure 6.

Figure 5: Efficiency comparison chart.

Figure 6: Inductor thermal comparison chart.
From the results of Figure 5, the parameter and efficiency comparison chart shows that the power inductor using the ferrite core — ITG P/N SLM534214A-1R0MHF — offers the highest efficiency because the ferrite offers a lower core loss at 500-plus KHz than the other two inductors. Its lower DCR also exhibits a significant advantage in thermal performance.

Conclusion

When design engineers need to quickly design products that meet customer dictated specifications and performance, ITG provides free inductor design tools that allow engineers to calculate the appropriate inductance, identify the part number that meets the circuit design requirements and quickly find the datasheet for review.

In addition, ITG also provides customers with customized and high-performance magnetic component solutions. If you do not find what you think will provide the best result for your design requirements, please contact ITG Engineering directly.