EE136 Presentation By Dan Lee Dec/6 th /2003 Soft Start Electromagnetic Interference

What is Soft Start? Why we need Soft Start? We want Converter to activate when proper voltage and current are set. We want Converter to start with narrow pulse width to prevent excess current from stressing components.

Soft Start 1

Start

Start and Soft Start

Start & Soft Start

What is E.M.I.? Any unwanted conducted or radiated signals that affect the circuitry. It requires three conditions to have E.M.I. On the circuitry. 1>Source 2>receiver 3>path

Conducted Mode E.M.I. Differential or Serial Mode Interference. E.M.I. Between two Lines Common Mode Interference The E.M.I. Between a Line & Ground

Example of In-Line Filter

How to prevent C.M. E.M.I. from the Switch section!

C.M. E.M.I. Preventing C.M. E.M.I. Is better than suppressing it with filters. Once C.M. E.M.I. Is flows through ground, it can propagate to multitude paths.

How to Calculate Components! Using Foster or Caur method isn’t recommended. Because of difficulty of finding Vo/Vin Transfer Function. CutOff Freq for C.M. is 18.5Khz. C.M. C2= Current / (2*Pi* Freq*Voltage) C.M. L1=1 / (C2*[4*Pi*Freq]^2) CutOff Freq for D.M. is 16Khz. D.M. L3=1/ (C4*[4*Pi*Freq]^2)

8Khz D.M. E.M.I.

18Khz CutOff D.M. E.M.I.

18Khz D.M. E.M.I. W/O L. Filters

1.8Mhz CutOff D.M. E.M.I.

C.M. E.M.I. 5Mhz, 30Volt

C.M. E.M.I. 30V,5Mhz W/O L1 & L2 I=30V*w*C=18.8mA

Thank You! Any Question?