Browse Prior Art Database

Combining Period Linear Frequency Jitter and Random Frequency Jitter to Reduce EMI Issue for Switching Mode Power Supply

IP.com Disclosure Number: IPCOM000035671D
Original Publication Date: 2005-Feb-25
Included in the Prior Art Database: 2005-Feb-25
Document File: 4 page(s) / 585K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

For power systems, the electromagnetic interference (EMI) issue caused by the 'Switching Mode Power Supply' is a major problem (Figure 1). The reduction of EMI issue is therefore one of the key points of today's research. In the following a method is introduced, which greatly reduces the amplitude of the switching current caused by EMI. There are some known methods to reduce the EMI issue, like the 'Period Linear Frequency Jitter Method' (PLFJM) and the 'Random Frequency Jitter Method' (RFJM). Figure 2 shows the frequency waveform and the switching current of the PLFJM. As can be seen in Figure 3, the EMI issue can be reduced by about 20dB when it is applied. In Figure 4, the frequency waveform and the switching current for RFJM is displayed. With this method the reduction is about 50dB (Figure 5).

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 66% of the total text.

Page 1 of 4

S

Combining Period Linear Frequency Jitter and Random Frequency Jitter to Reduce EMI Issue for Switching Mode Power Supply

Idea: Dr. Gong Xiaowu, SG-Singapore

For power systems, the electromagnetic interference (EMI) issue caused by the 'Switching Mode Power Supply' is a major problem (Figure 1). The reduction of EMI issue is therefore one of the key points of today's research. In the following a method is introduced, which greatly reduces the amplitude of the switching current caused by EMI.

There are some known methods to reduce the EMI issue, like the 'Period Linear Frequency Jitter Method' (PLFJM) and the 'Random Frequency Jitter Method' (RFJM). Figure 2 shows the frequency waveform and the switching current of the PLFJM. As can be seen in Figure 3, the EMI issue can be reduced by about 20dB when it is applied. In Figure 4, the frequency waveform and the switching current for RFJM is displayed. With this method the reduction is about 50dB (Figure 5).

To further reduce the EMI issue, it is proposed to combine these two methods. The circuitry for this new method can easily be implemented based on the circuitry for the PLFJM by replacing the fixed time delay after the oscillator circuit with a random time delay. Figure 6 shows the resulting frequency waveform and switching current. Simulations imply that with this combination the EMI issue can be reduced by about 80dB (Figure 7).

Figure 1: Switching Current Spectrum without EMI Reduction

© SIEMENS AG 2005 file:...