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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

Publishing Venue

Siemens

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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).