EMI of switch power source designs experience

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1, the EMI interference source of the power source of EMI source switch of switch power source is reflected centrally wait in diode of power switch canal, commutate, high frequency transformer, external environment basically comes from electrified wire netting to the interference of switch power source shake, radiate of be struck by lightning, outside. (1) the condition that canal of switch of power of power switch canal works to be changed circularly quickly in On-Off, dv/dt and Di/dt are changed in urgent revulsion, accordingly, power switch provides the main interference source of coupling of since electric field, also be the main interference source of magnetic field coupling. (2) the Di/dt that the EMI origin of high frequency transformer reflects high frequency transformer to feel corresponding in leakage centrally alternates circularly quickly, because this is high frequency,transformer is the important interference source of magnetic field coupling. (3) the body of EMI origin concentration of diode of rectification diode commutate restores character to go up reversely now, what restore electric current reversely is bit more intermittent can be in inductance (down-lead inductance, stray inductance) produce tall Dv/dt, bring about strong electromagnetism interference thereby. (4) PCB says well and truly, PCB is afore-mentioned coupling passageways that violate a source, the actor bad of PCB, afore-mentioned pair of direct and corresponding EMI source low-key stand or fall. 2, transmission passageway of EMI of switch power source is classified (one) the transmission passageway of conducted interference (1) the coupling that allow a gender (2) perceptual coupling (3) resistor coupling A.

The resistor that internal resistance of common power source produces conducts coupling B.

The resistor that impedance of communal ground wire produces conducts coupling C.

The resistor that public line impedance produces conducts coupling (2) the transmission passageway that radiation disturbs (1) in switch power source, yuan of parts of an apparatus or appliance that can make source of faze of spoke blackberry lily and lead all can be assumed be aerial, use couple pole thereby child with magnetism occasionally extremely child theory undertakes an analysis; Canal of switch of diode, capacitance, power can assume it is couple pole child, inductance coil can be magnetism idol suppose extremely child; (2) when doing not have shield, couple pole child, magnetism idol extremely child, the electromagnetic wave of generation transmits a passageway to be air (can be free space suppose) ; (3) when having shield, consider the aperture of shield and hole, undertake analytic handling according to the mathematical model of leak field. 3, 9 big step are in low-key of EMI of switch power source in switch power source, the mutation of voltage and electric current, namely tall Dv/dt and Di/dt, it is the main reason that its EMI produces. The measure of EMC design technology that implements switch power source basically is based on the following at 2 o'clock: (1) the interference source that reduces generation of place of power source itself as far as possible, use the method that restrains interference or generation to disturb yuan of lesser parts of an apparatus and circuit, have reasonable position; (2) the EMI that controls power supply through the technology such as wave of ground connection, filter, screen and the EMS that increase power supply. Will tell apart, 9 big step are respectively: (1) reduce Dv/dt and Di/dt (reduce its peak value, slow down its slope) (2) pressure quick the rational application of resistor, in order to reduce surge tension (3) damp network has been restrained strong (4) use soft the diode that restores character, in order to reduce high frequency paragraph of EMI (5) active power factor is corrective, with etc harmonic corrective technology (6) the filter of power supply cord that uses reasonable design (7) reasonable ground connection processing (8) significant screen step (9) reasonable PCB is designed 4, high frequency transformer leaks the controls high frequency transformer leakage of feeling, accordingly, control leakage feeling becomes the EMI that solves high frequency transformer to bring principal faced problem. Reduce high frequency transformer leakage feeling cuts a point twice: Electric design, craft is designed! (1) choose appropriate magnetism core, drop leakage move. Leakage feeling and former edge circle several square become direct ratio, reduce v/LIT all over the ground number to be able to drop leakage move significantly. (2) reduce the insulation layer between winding. One kind says now for " gold is filmy " insulation layer, ply 20 ～ 100um, pulse puncture voltage can amount to thousands of bend over. (3) add the coupling factor between winding, reduce leakage feeling. 5, the screen of high frequency transformer is opposite to prevent the leakage magnetism of high frequency transformer all round circuit generates interference, can use screen to bring screen the leakage magnetic field of high frequency transformer. Screen belt is made by Copper Foil commonly, circle in transformer exterior a week, have ground contact, screen band appearance to leakage magnetic field it is annulus of a short circuit, restrain leakage magnetic field thereby more large-scale leak. High frequency transformer, mix between magnetic core opposite displacement can happen between winding, bring about high frequency transformer to produce noise in the job thereby (howl cries, oscillatory) . To prevent this noise, need takes consolidate step to transformer: (1) with epoxy resin magnetic core (for example magnetic core of EE, EI) 3 interface undertake sticking receiving, restrain the generation of opposite displacement; (2) with " vitreous bead " (Glass Beads) agglutinant felt magnetic core, the effect is better. CNC Milling CNC Machining