开关电源控制芯片中减小EMI的一种电路实现方法.pdf

3 8 1 ( ) V o.l 38 No. 1 2010 2 Journa l of F uzhou U n iversity( N a tura l Sc ience) F eb. 20 10 1000 - 224 3( 2010) 01- 0058- 0 6 EM I (, 350108) , , EM I . , PWM , , EM I. , EM I. ; ; EM I; TP 273 A A m ethod of circuit implem entations on reducing EM I in the control chip of the sw itching power supply QU A i- w en ( College o f Physics and Inform ation Eng inee ring, Fuzhou U n ive rsity, Fuzhou, Fu jian 35010 8, Ch ina) Abstract: A ccording to suppressing no ise source, th is pap er proposes a m ethod o f circu it mi plem enta t ions on redu cing EM I in the con tro l ch ip o f the sw itch ing pow er supp ly b ased on the spread- sp ectrum theory. Th is m ethod adopts triangu lar m odu lating signal to m odu late the oscillator frequ ency. B ecause of the sw itch ing frequency o f the sw itching pow er supply w ith PW M ( Pu lse- w idth m odulation) con tro lling decided by the oscillator frequ ency, m odulating the oscilla tor frequency is the sam e as m odu la t ing the sw itch ing frequency. So u sing this techno logy, the peak energy focu sing on the sw itching fre quency and its h igher harm onic is exp anded, and the EM I no ise is redu ced. A ccord ing to analysis on spectrum of the osc illators output pu lse w ave, it verifies the oscillator stru cture this paper proposed can rea lize redu cing EM I no ise source.