his is the fourth article in a series of articles devoted to the design, test, and EMC emissions evaluation of 1- and 2-layer PCBs that contain AC/DC and/or DC/DC converters, and employ different ground techniques [1, 2, 3]. In this fourth article, we are still focused on the DC/DC power converter board (2-layer PCB). In this article, we will evaluate the implementation of several EMC countermeasures and present the radiated emissions results according to CISPR25 Class 5 limits.
The third article [3] presented the radiated and conducted emission results from the baseline design which did not contain any EMC countermeasures. The results showed multiple failures in both radiated and conducted emissions. This fourth article presents a systematic approach to improve these failures by populating the PCB with optional EMC countermeasures on component pads that have already been designed into the PCB layout and showing their impact on the radiated emissions. The countermeasures are presented in an order that we would typically follow in an EMC diagnostic session where, due to time restrictions, not every single permutation of EMC countermeasure will be tested. The EMC countermeasures are illustrated in Figure 1 as purple dashed boxes labeled EMC-A through EMC-F.
The impact of these countermeasures is discussed next. The article concludes with a brief description of what can be expected in the next article in the series.
Typically, these 1nf capacitors help filter the noise in higher frequencies. However, as the plot in Figure 4b shows, they had a minimal impact on radiated emissions performance in the upper-frequency range of this band.
Typically, this inductor helps to reduce emissions in this range by filtering the input and attempting to prevent noise from getting onto the harness where the 2-meter wire length acts as an effective re-radiator. However, as Figure 5b shows, it had a minimal impact in the 150kHz – 30MHz range.
The results of this testing suggest that the noise that is causing emissions at these lower frequencies is either radiating directly from the PCBA (Printed Circuit Board Assembly) or common-mode emissions (rather than differential mode noise) conducting out on the wire-harness. This leads us to our next countermeasure of shielding the switching inductor L1. Due to the ineffectiveness of both the 1uH inductor and the 1 nF capacitors, they were removed from the sample before testing the next countermeasure.
As the plots show, the inductor had a substantive impact, not only in the 0.9-2 MHz range but also in the 25 – 30 MHz range. Because the objective of this shielded inductor is to reduce the emissions by capturing the electric field, a significant improvement was observed in the monopole antenna range (150kHz-30MHz). This justifies changing the measurement setup to the biconical antenna to evaluate the improvements in the 30 – 300 MHz range. The results are shown in Figure 5 (Note: From this point forward, measurements above 300 MHz are not captured due to passing results in baseline testing).
This shows a significant reduction in the emissions measured with the antenna in the vertical polarization around 36 MHz but has minimal impact on the horizontal polarization. This also shows a smaller reduction in emissions around 180 MHz.
Next, the snubber is removed from its location across the catch diode and placed across the FET which is internal to the IC. This snubber is placed on the placeholders R2 and C2 (EMC-B). The radiated emissions results are shown in Figure 7.
This shows a slight reduction in the emissions measured with the antenna in the vertical polarization around 36 MHz but has minimal impact on the horizontal polarization. This also shows a reduction in emissions around 180 MHz.
This shows a significant reduction in the emissions in the 30 – 80 MHz range and around 180 MHz. This technically passes CISPR 25 Class 5, but due to expected lab-to-lab variation greater margin is desired in the average measurement around 180 MHz before finalizing the design.
Figure 9 on page 48 shows the radiated emission measurements in the 150 kHz – 30 MHz range while Figure 10 shows the results in the 30 -1,000 MHz range.
The conducted emissions countermeasures were very effective at reducing radiated emissions in both the 150kHz – 30MHz and 30MHz – 300MHz ranges. These DUT modifications are preserved for the following sections of this article.
It is important to note that the shield frame was placed without a shield lid in this first evaluation. This is being evaluated, since in some cases, sufficient emissions reductions can be achieved with only the frame component. Figure 11 shows the radiated emissions results in the frequency range 150 kHz – 30 MHz, while Figure 12 shows the results in the range 30 – 1,000 MHz.
The addition of the shield frame to the conducted emissions countermeasures provides significant decreases in emissions in the range of 150kHz – 300MHz and makes the emissions low enough to pass CISPR 25 Class 5 radiated emissions limits.
If this SMPS was a product that was intended for sale, the next step would be to start removing the EMC countermeasures one by one to reduce the Bill of Materials (BOM) cost of each unit produced. An example of this would be trying to remove the IHLE 5.6 uH inductor in favor of a cheaper inductor. In our previous trials, this increased emissions in the 0.9 – 2MHz range above the average limit. An evaluation was performed by exchanging the IHLE 5.6 uH E-field shielded inductor (L1) for the original IHLP 5.6uH magnetically shielded inductor (L1) and a shield lid was placed on the shield frame. The radiated emissions results with the shield lid and L1 swapped are shown in the frequency range 150 kHz – 30 MHz in Figure 13.
Based on the results presented in this article, we recommend finalizing the design to meet radiated emissions requirements (CISPR25 Class 5) with the following countermeasures populated on the baseline design:
EMC A – Front End Filter
C7 = 2.2uF (with additional 2.2uF or change to 4.7uF)
L2 = 2.2uH
C7 = 2.2uF (with additional 2.2uF or change to 4.7uF)
C9 = 10nF
EMC-B – Internal FET snubber
Not populated
EMC-C – Shielded Switch Inductor
Preserve original IHLP 5.6uH magnetically shielded inductor
EMC-D – Catch diode snubber
Not populated
EMC – E – Output high-frequency capacitance
C4 = 10nF
EMC-F – Shield frame and lid
Populate both frame and lid
- Adamczyk, B., Mee, S., Koeller, N, “Evaluation of EMC Emissions and Ground Techniques on 1- and 2-layer PCBs with Power Converters – Part 1: Top-Level Description of the Design Problem,” In Compliance Magazine, May 2021.
- Adamczyk, B., Mee, S., Koeller, N, “Evaluation of EMC Emissions and Ground Techniques on 1- and 2-layer PCBs with Power Converters – Part 2: DC/DC Converter Design with EMC Considerations,” In Compliance Magazine, June 2021.
- Adamczyk, B., Mee, S., Koeller, N, “Evaluation of EMC Emissions and Ground Techniques on 1- and 2-layer PCBs with Power Converters – Part 3: DC/DC Converter – Baseline EMC Emissions Evaluation,” In Compliance Magazine, July 2021.
- https://www.mouser.com/new/vishay/vishay-IHLE-efield-shield-inductors