The design avoids the measure of EMI when switch power source

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EMI (Electromagnetic Interference) , electromagnetism interference, be after pointing to electromagnetic wave and electronic component action and the interference phenomenon of generation, conducted interference and radiate disturb two kinds. Conducted interference is to point to the signal coupling that gets on sth resembling a net of an electrified wire netting through electric medium (disturb) to sth resembling a net of another electrified wire netting. Faze of spoke blackberry lily is to show interference source passes a space its signal coupling (disturb) to sth resembling a net of another electrified wire netting, in high speed PCB and systematic design, of high frequency line, integrated circuit bring foot, of all kinds receive plug-in unit to wait to become the radiate that has aerial character possibly to violate a source, can emit electromagnetic wave and affect other system or the regular job of other subsystem inside this system. The characteristic of EMI of switch power source changes unit at the energy of switch condition as the job, rate of change of the voltage of switch power source, electric current is very high, the interference strength of generation is greater; During interference source basically is centered in power switch and the radiator that is linked together to it and tall smooth transformer, the position that violates a source at digital circuit relatively is relatively clear; Switch frequency is not tall (from a few conspicuous and number hertz) , main interference form is conducted interference and near field interference; And presswork circuit board (PCB) walks along a line to use manual wiring normally, have bigger optional sex, this increased the difficulty of the extraction of PCB distributinging parameter and estimation of near field interference. 1MHZ less than----Give priority to in order to need modular interference, increase X capacitance to be able to solve 1MHZ---5MHZ---Wrong standard in all the model mixes, use an input to carry and a series of X capacitance will filter feels interference except difference and divide separate out is which kinds of interference exceed bid and solve;5M---Above is given priority to with feeling interference in all, use restrain the method that feels in all.

To crust ground connection, surround 2 rounds to be able to be disturbed to 10MHZ above with a magnetism on ground wire have bigger attenuation (Diudiu2006); to 25- - 30MHZ can be used nevertheless increase the right Y capacitance, small magnetism loop that includes cupreous skin, change to a crewel is received before line of PCBLAYOUT, output and be circled outside transformer, circle 10 rounds the least, in output rectification manages two end and RC filter.

30---50MHZ is general it is MOS is in charge of high speed to debut close to cause, can use increase MOS drive resistance, RCD amortize circuit uses 1N4007 to be in charge of slow, voltage of VCC power supply is solved with 1N4007 slow canal.

100---200MHZ is general it is to output rectification canal to restore electric current to cause reversely, magnetism bead can be strung together on rectification canal PFCMOSFET and PFC diode are stemmed from for the most part between 100MHz-200MHz, MOSFET and PFC diode string together magnetism bead to have the effect now, horizontal way can solve a problem basically, but perpendicular direction is very helpless the radiate of switch power source can affect the frequency under 100M only commonly paragraph.

Also can be in MOS, add on diode draw return circuit accordingly, but efficiency can be reduced somewhat. The design avoids the measure of EMI when switch power source: 1.

If switch is in charge of,the ground of utmost of area of PCB Copper Foil noise circuit node reduces; leakage pole, collector, the first time the node of class winding, etc. 2.

Make input and output end are far from noise component, if transformer line is wrapped, transformer magnetism core, the carbon fin that switch is in charge of, etc. 3.

Make noise component (wrap like the transformer line that did not cover, the transformer magnetism core that did not cover, with switch canal, etc) be far from crust brim, because be below normal operation,crust brim stands by the ground wire outside probably. 4.

If transformer does not have screen of use electric field, want to maintain shield and carbon fin to be far from transformer. 5.

Reduce the area of annulus of the following electric current as far as possible: Sub (output) rectifier, parts of an apparatus of primary switch power, grid (base) drive circuitry, assist rectifier. 6.

Not the door extremely (base) drive returns annulus of make a present of circuit of switch of Lu Hechu class or lump of auxiliary commutate circuit. 7.

Adjust optimize damp resistance, make it does not produce ringing sound in the dead band time of switch. 8.

Prevent saturation of inductance of EMI filter wave. 9.

The shield that makes the component of bend node and sub circuit is far from primary circuit or the carbon fin that switch is in charge of. 10.

The swing node that maintains primary circuit and component noumenon are far from screen or carbon fin. 11.

Make the EMI filter of high frequency input stands by input cable or connector end. 12.

The EMI filter that holds high frequency output stands by terminal of output electrical wiring. 13.

Make on EMI filter certain distance maintains between the Copper Foil of PCB board and component noumenon. 14.

A few resistance are put on the circuitry of the commutator of auxiliary coil. 15.

In resistor of damp of the paralell connection on magnetism marvellous coil. 16.

In output RF filter resistor of damp of two upright paralell connection. 17.

Allowing to put capacitor of 1nF/500V pottery and porcelain when PCB is designed still perhaps can be a string of resistor, bond is between the simple Jingduan of transformer and auxiliary winding. 18.

Maintain EMI filter to be far from power transformer; to avoid fixed position to carry a department in what circle a bag especially. 19.

In PCB area sufficient condition falls, the foot that can keep winding of screen of transfer to a lower level to use on PCB the position with the damper that put RC, RC damper but bond is in screen winding two end. 20.

The leakage that if the space allows, is in charge of in effect of switch power field extremely and capacitor of down-lead of a small radial is put between door pole (rice straps capacitance, 10 skins law / 1 kilovolt capacitance) . 21.

A small RC damper is put to output end in dc if the space allows. 22.

The carbon fin that does not provide AC electrical outlet and primary switch leans together. CNC Milling CNC Machining