Anti-noise circuit of switch power source

 

 

EMI filter and π filter is similar, but actually it is filter of a two-way LC. Its action on one hand the interference that filter enters except change of communication town report, on the other hand filter provides the noise of a generation except switch, prevent its to enter the pollution that creates didymous electrified wire netting to input power supply cord.

 

The C4 of capacitor C1 ～ that when comprising LC filter jointly with inductor of EMI filter wave, uses, want to choose the high-pressured film capacitor with high frequency good character or capacitor of pottery and porcelain normally, the look value of a quantity of these capacitor can be in 0.005 ～ choose between 0.1μF, but the working tension that should note these capacitor must satisfy a requirement.

 

 

Surge basically restrains circuit by overvoltage implement give priority to form. Normally the setting is after inductor of EMI filter wave, but before circuit of rectification filter wave. Surge is restrained is to use the series connection impedance of inductor of EMI filter wave to prevent to exceed their rated instant energy. EMI inductor reduced instantaneous voltage peak value greatly, lengthen it on time, can raise surge to restrain circuit place to use the working life of component so.

 

Must notice: The internal resistance character that different surge restrains component place to establish ties is different also. Metallic oxide rheostat (MOV) guide when connecting, resistance is very tall, and semiconductor surge is restrained implement resistance is lower. When producing surge, restrain implement resistance can be affected add in the rated voltage above its. For example, rheostat of 180V metal oxide, instantaneous voltage can rise to 230V. Reason is in choose filter wave capacitor and surge to restrain implement when, should consider this.

 

 

When circuit is started, the C5 big capacitor that normal voltaic pulse discharges completely already via be opposite after rectification undertakes charging, make the upright voltage of capacitor jumps change, the surge electric current that causes thereby compares virtual value of average input electric current likely 10 times big still. So big surge electric current can cause rectifier damage likely. For this, can receive RT of a thermistor at the back of of EMI filter normally. The resistance when thermistor low temperature is between 6 ～ 12Ω , after starting, thermistor is heated, the resistance after heating has 0.5 ～ only about 1Ω .

 

Circuit of application of interference rejection of two class EMI is like switch regulated power supply graph 2-2 place is shown. This circuit is main wait for composition by L1, R1, C1, C2, L2. This is two class series connection in all modular filter, use pair of asymmetry and symmetry interference signal to undertake inhibition. In all modular filter has effect of double filter wave, already but filter is divided enter all sorts of symmetry inside machine or asymmetry interference by alternating current net, the Gao Cixie wave that can prevent itself of power source of the switch inside machine to arise again enters city electrified wire netting and cause interference to other and electric equipment. C1, C2 is used at bypass to need modular interference, l1, L2 is used at attenuation in all modular interference.

 

After modular filter is purified, two class change classics of voltage of alternating current source into in all jam-free alternating voltage, circuit of switch stabilized voltage is supplied after wave of filter of commutate of classics commutate bridge, C6 again.