Under the difference mold unwanted signal function, the electric current which the noise source produces i, has the direction opposite magnetic flux in the magnetic core Phi, the magnetic core medium to does not have the magnetic flux, the coil inductance nearly is zero. Therefore cannot suppress the difference mold unwanted signal.
Under the mold unwanted signal function, the magnetic flux direction which two coils produces is altogether same, has the function which mutually strengthens, each coil inductance value for alone exists when two times. Therefore, this kind of connection magnet coil has the very strong inhibitory action to altogether the mold disturbance.
In the electric circuit inserts altogether the mold impedance coil between the electrical network and the rectification bridge, this impedance coil presents the extremely low impedance to the electrical network frequency bad lay wire side electric current, thus is extremely low to the electrical network pressure drop; But high frequency altogether mold noise which produces to the power source, the equivalent impedance is higher, thus may obtain the hope the insertion loss.
2.2 impedance coils L11 and C11 composition low pass filter
The impedance coil L11 equivalent inductance is L, takes the input by the power source end, the electrical network direction takes the output.

Its transfer function is
G (s) = = (1)
The peak-to-peak value is
A (omega) =|G (j omega) |= (2)
The phase is
L (omega) =201gA (omega) = - 201g (3)
When low frequency band omega <<, A (omega) �?1, L (omega) �?0
When high frequency band omega >>, A (omega) �? L (omega) �?- 401g omega the LC11 like chart 5 shows. Thus it can be seen, above LC network composition low pass filter, may filter omega above the 0=1/LC11 higher harmonic.


2.3 altogether molds and difference mold filters plan
This electric circuit main EMI question is the power source noise spreads to the electrical network, original altogether mold impedance coil L11 and electric capacity C11 and the C12 composition filter circuit will become the electric circuit. L1, L2, C1 may except the bad mold disturbance, L3, C2, C3 be possible except altogether the mold disturbance. L1, L2 is not the easy magnetic saturation material; C1 may choose the ceramic electric capacity; L3 is altogether the mold impedance coil; Designates C=C2=C3 and cut-off frequency fo, then may [ (2 pi fo) 2C ] calculate L3 according to L3=1/; Designated C1 and cut-off frequency fo, may [ 2 (2 pi fo) 2C1 ] calculate L1 and L2 according to L1=L2=1/.
2.4 cushions electric circuits
Because the switch fast passes breaks, the switch electric current, the voltage waveform are the pulse form, has the noise pollution, has increased the power source output ripple, has affected the power source performance.
In the electric circuit, inputs for exchanges 220V, after the rectification on the electric capacity voltage for exchange 有效�? 1.2 ~ 1.4 times, namely is approximately biggest time for Ucm=220×1.4=308V. Moreover, the transformer vice- on the one hand converts into to the original on the other hand voltage Up=Un×88/9, Un takes the vice- side first winding the voltage, generally is about 9V, causes the constant voltage output is 5V. Then Up=88V. Therefore, the switch shuts off time must withstand total voltage Ut=Ucm + Up=308 + 88=396V. Obviously has the necessity to carry on to the switch 过压保护. The electric circuit selects the TOPSwitch switch chip, its interior has 过压保护 and the cushion electric circuit. In order to insure in order to, but also increased the exterior cushion electric circuit, is composed by R and C.
After has not joined the cushion electric circuit and joins the cushion electric circuit switching valve voltage ut and tube electric current ic and shuts off power loss pt the profile to show. After adds the RC cushion electric circuit, the switch voltage rise speed slows down, the noise was weaken, has suppressed EMI, and the switch power loss changed slightly, caused the pipe not to send because has flowed hotly has damaged. In cushion electric circuit R clears in the switch, when electric capacity C electric discharge limits flows the function, avoids to the switching valve the impact.

Clears when regarding the switch electric current impact, because has transformer original side coil Np to limit the class, has not added in the electric circuit limits flows the inductance.
2.5 photoelectricities isolation
In the Flyback electric circuit uses the PC817 light 耦对 main circuit and the control circuit carries on the isolation. In the power circuit, the switch control count for much, the precision, the stability request high, also the control circuit is sensitive to the noise, once has the noise, in the control circuit control signal can the disorder, seriously affects the power source the work and the performance. Therefore, carries on with PC817 the power source in two parts the isolation, had like this then prevented the noise spreads through the conduction way to the control circuit in.
3 conclusions
Analyzes and uses the corresponding suppression method through EMI, the design switching power supply has the anti- electronmagetic interference to be strong, power source stability high characteristic. In the sewing machine servocontrol, has satisfied to the Mitsubishi module (IPM) the actuation control, safely causes the electrical machinery movement reliable, to be stable.
The company introduces
---- A village electron (Beijing) the limited company is as well as external throws the company by the power source profession and the electromagnetic compatibility profession expert which the capital sets up together. Is a fair research and development, the production, the sale is a body electronic products manufacturer, the company has the advanced production assembly line and each kind of check-out facility, produces the product satisfies the different user the demand.
---- Specialized production management: Electronic products and so on switching power supply, filter, shielding material as well as absorption part. The product main application domain includes: Military, situation and so on electric power, medical, instrument measuring appliance, communication, automobile electron. The company main staff they have the deep power source and the electromagnetic compatibility rationale as well as several years power source and the filter product design experience, causes the design low loss, the high efficiency product which we succeeds, to satisfy the customer to each kind of power source and the filter as well as the electromagnetic compatibility product demand, and has a higher prestige in the customer.
The company main product includes:
Switching power supply class
1. low power power sources (3W~500W) including - module power source, net shell power source, bare board power source, adapter
2. high efficiency power sources (600W~10000W) including - general power source, correspondence power source, direct current operation power source
3. contravariant power sources (35W~5000W) including - sine wave inversion, Fang Xianbo inversion
4. solar energies power sources (50W~5000W) including - solar energy charge controller, solar energy control system
5. other power sources
Filter class
1. plugs types filter 2. inserts the needle type filter 3. single-phase filters
4. three-phase filters 5. frequency changers special-purpose filters 6. direct current filters
7. military filters 8. �?pass the filter 9. filters couplings
10. screened rooms filters
Other kinds:
Shielding material and absorption part
- Our company specialized solution electromagnetic compatibility and the national troops sign -
Company: Village electron (Beijing) limited company
Telephone: 010-52568762
Facsimile: 010-52568763
Contact person: Mr. Ma (13.269766958 billion)
Mailbox: Cuntai200@sohu.com
Address: The Beijing Changping area returns to Long Guanlong crown building 4
Websitewww.cuntai.com