As the switching power supply is switched on and off, the current in the inductor also fluctuates around the effective value of the output current. So there will be a ripple of the same frequency at the output. The ripple is related to the capacity of the output capacitor and the ESR. In addition, the switching power supply generally uses bipolar transistor or MOS tube, no matter which, in its conduction and cut-off, there will be a rise time and fall time. At this time, there will be a noise in the circuit with the same frequency as the voltage rise and fall time or an odd multiple frequency, generally tens of MHz. Similarly, the diode in the reverse recovery moment, its equivalent circuit for resistor capacitor and inductor series, will cause resonance, the noise frequency is also dozens of MHz. These two kinds of noise are generally called high frequency noise, and the amplitude is usually much larger than the ripple.
If it is an AC/DC converter, in addition to the above two kinds of ripple (noise), there is AC noise, the frequency is the input AC power supply frequency, about 50 ~ 60Hz. There is also a common mode noise caused by the equivalent capacitance of the power components of many switching power supplies that use the housing as a radiator.
Disadvantages of Ripples voltage:
1, easy to produce harmonics in the electrical appliances, and harmonics will produce more harm;
2, reduce the efficiency of the power supply;
3, strong ripple will cause the generation of surge voltage or current, resulting in the burning of electrical appliances;
4. It will interfere with the logical relationship of the digital circuit and affect its normal work;
5, will bring noise interference, so that the image equipment, audio equipment can not work normally.