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In view of the different frequency band switch power supply EMI suppression method

by:Fuyuang     2020-05-21
In the design of switch power supply EMI is important one annulus. Many developers are racking their brains in the electromagnetic interference problem, only for the circuit would be able to pass the test. But EMI generated in the circuit is very complicated, the interference of frequency are also different. The interference of some lower just some minor adjustments can be corrected, and some of the larger interference from various aspects is needed. This article will introduce according to different frequencies of switch power supply EMI suppression method. Within 1 mhz1mhz, give priority to with differential mode interference. The solution is as follows: (1) increasing capacitance X; (2) add differential mode inductance; (3) small power sources can PI type filter processing ( Suggest near the transformer electrolytic capacitor can choose bigger) ; 1 mhz - 5 mhz1mhz - 5 MHZ, differential mode common-mode mix, the input capacitance parallel series of X is used to filter out bad touch interference and analyze what excessive interference and to solve: (1) for differential mode interference exceeds bid adjustable capacitance X, adding differential mode inductors, the differential mode inductance; (2) for excessive common-mode interference can add common-mode inductor, choose reasonable inductance to restrain; (3) can also change the rectifier diode characteristics, a pair of fast diode as FR107, a pair of ordinary 1 n4007 rectifier diode. More than 5 MHZ more than 5 m is given priority to with common touch interference, adopt the method of inhibition were touched. The shell for ground and on the ground with a circular and string around 2 - 3 laps to more than 10 MHZ interference has large attenuation effect; Can choose close to the transformer core stick copper foil, copper foil closed loop. Deal with the absorption of back-end output rectifier circuit and primary circuit is the size of the shunt capacitance. 20 - 30 MHZ (1) for a class of products can be used to adjust of Y2 or capacitance change Y2 capacitance position; (2) adjust the Y1 capacitance between a secondary side position and parameter values; (3) outside the transformer bread copper foil; Transformer is the layer and the shielding layer; The winding arrangement of adjusting transformer. (4) change PCBLAYOUT; (5) output line in front of the pick up a small common mode of bifilar winding inductance; 6 on both ends of the output rectifier tube parallel RC filter and reasonable adjustment of parameters; 7) between the transformer and MOSFET BEADCORE; Today in the input voltage of the transformer with a small capacitance. Pet-name ruby can increase with MOS resistor. 30 - 50 mhz30 - 50 MHZ, the common MOS tube high-speed opening shut off. The solution is as follows: (1) can increase the MOS resistor; (2) RCD snubber circuit using 1 n4007 slow tube; (3) the VCC power supply voltage in 1 n4007 slowly to solve; (4) or output line front-end concatenated a little bifilar winding common-mode inductor; 5 D - in MOSFET S foot a little absorbing circuit in parallel; 6. Add BEADCORE between transformer and MOSFET; All landowners in the input voltage of the transformer and a small capacitor; Heart was PCB LAYOUT when large electrolytic capacitors, transformers, MOS circuit composed of ring as small as possible; Pet-name ruby transformer, the output diode, the output wave of electrolytic capacitor circuit loop as small as possible; 50 - 100 mhz50 - 100 MHZ, generally is the output rectifier tube caused by the reverse recovery current. The solution: (1) can be on the rectifier magnetic bead; (2) adjust the absorption of output rectifier circuit parameters; (3) can change the secondary side jumper Y the impedance of the capacitor branch, such as PIN feet add BEADCORE or concatenated appropriate resistance; (4) can also change the MOSFET, the ontology of output rectifier diode to space radiation, Such as iron clip card MOSFET; Iron clamp DIODE, change the radiator of the ground) ; 5. Increase shielding copper foil inhibition to space radiation. In view of the power supply more than 200 MHZ, this kind of power supply basic radiation is very small, can generally be EMI standard. In addition it is important to note that high frequency switch power supply transformer circuit is usually the shielding layer. In addition to other factors, switching power supply circuit board layout of electronic components for EMI suppression effect is also very large, so to do a good job of the layout of the components are become very important, mechanical shell is also the key to whether can pass the electromagnetic interference. Can see the influencing factors of EMI is very much, but it's also a problem will be the cause of the headache.
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