One, how do ripple and noise produce

 

Following graphs are shown 1 times, inside blue line draw a frame round is ripple, and outside blue line draw a frame round is noise, although ripple and noise are reflected go up in a weaveform, but what belong to different share.

 

Because switch power source is carrying the wave motion that deliver discontinuous energy and causes to output,the generation of ripple is, this fluctuant frequency is the frequency that switch is in charge of, the voltaic ripple rate when the size of amplitude and design and capacitance of output filter wave are concerned. And the generation of noise basically is switch canal is in guide connect or Guan Duan instant, by its circuit medium or the ringing appearance that the inductance of the parasitism on parts of an apparatus and capacitance cause, frequency is taller after noise magnifies, amplitude is bigger also.

 

Graph 1

 

2, how to reduce ripple

 

The generation of ripple delivers spiccato energy to cause by switch, will begin from the interior design of switch power source, can increase the frequency that switch is in charge of, the energy that makes be delivered every time is reduced reduce ripple thereby, also can increase the inductance that delivers energy to be worth L, make choppy peak value of electric current is reduced, reduce the fluctuant scope of ripple thereby.

 

From module exterior, carry in the client especially, can increase capacitance of output filter wave to reduce ripple, but cannot increase electric capacity indefinitely, because module of most switch power source has the biggest load that allow a gender,restrict.

 

3, how to reduce noise

 

1, power source PCB takes line and position

 

Capacitance of output filter wave is placed reach a line crucial to noise, if the graph is shown 2 times, in traditional design because arrive at the impedance of every capacitance different, so high frequency electric current allocates in 3 capacitance inhomogenous, in improving a design, can see every loop length comparatives namely high frequency electric current is met equal apportionment arrives in every capacitance, voltaic input outputs method to must pass capacitance first, and the shop copper of cloth board as far as possible to capacitance polar astringent.

 

Graph 2

 

If PCB is multilayer board, can choose and layer of principal current loop is the closest ground of a Fu, the settlement with Fu OK and effective ground noise problem, attention, assure the integrality of Fu ground as far as possible.

 

2, circuit absorbs noise

 

Increase RCD to absorb switch to be in charge of the voltage aiguille of the generation when closing, will reduce the noise that coupling carries to output. Restore time what choose field effect canal commonly to want slower than diode D1 2~3 reversely times, form direct electric current in order to avoid, this electric current can produce very strong magnetic field, can increase output noise, can decelerate what switch is in charge of to guide so through grid resistor R4 a speed. It is OK to involve rate to be not affected in grid resistor paralell connection a diode D2 is like a graph 3 are shown.

 

Graph 3

 

Two end of DS of canal of OK and attendant effect are shunt-wound if the graph is shown 3 times,circuit of a RC also can reduce noise effectively, capacitance C2 is controlled in 100PF~300PF commonly, capacitance has been worth congress to bring about the switch loss that field effect runs to increase, resistor R2 is chosen commonly be less than 10Ω resistor.

 

Diode guides in high speed when connect and closing, between retrorse convalescence, the parasitism inductance of diode and capacitance can produce high frequency vibration, to restrain high frequency oscillation to be able to be in two end add diode RC amortize circuit is shown 3 times like the graph, resistor R3 is in commonly 1Ω~100Ω , capacitance C3 is in commonly 100pF~1nF, if frequency of power source job is inferior, efficiency satisfies the word of the requirement, diode D3 can choose to restore the diode with slower time reversely.

 

3, transformer design reduces noise

 

When the winding of transformer carries high frequency electricity, transformer will turn effective magnetic field into aerial, transformer winding bears again bouncing voltage, namely transformer also turned electric field into aerial, be in the first time the noise electric current that Faraday screen layer increases to be able to collect segregation border to be in between class, give move arrives former border district, but Copper Foil should be taken for very thin Copper Foil, avoid eddy current loss as far as possible and reduce leakage feeling, attention, extreme of cupreous screen layer is not due join, can form magnetism short circuit otherwise.

 

Use sandwich to circle a law to be able to make the first time class winding coupling is more close together, make leakage feeling is able to reduce, reach the goal that reduces noise thereby, also can reduce with crust of 6 screen metal external noise interference.

 

Summary

 

When designing power source, afore-mentioned a few methods can reduce the ripple noise of output, not be whole method of course; If choose finished product power source, no matter be adapter of module power source, common switch power source, power source, the job of this part designs manufacturer to finish by power source commonly, the output ripple noise that the client needs to pay close attention to norms book to mention expressly only can. If ZLG sends the module power supply of far electron, the ripple noise of model of meeting line out is worth, be like E_UHBDD-10W series, typical cost is 150mV VP-P.