Ripple and Noise Generation Causes in Switching Power Supplies
Switching power supply (including AC/DC converter, DC/DC converter, AC/DC module and DC/DC module) compared with linear power supply, the most prominent advantage is the conversion efficiency is high, generally up to 80% to 85%, high up to 90% to 97%; Secondly, the switching power supply using a high-frequency transformer instead of the bulky frequency transformer, not only the weight to reduce the size of the volume is reduced, so the The application range is getting wider and wider. However, the disadvantage of switching power supply is due to its switching tube working in the high-frequency switching state, the output ripple and noise voltage is larger, generally about 1% of the output voltage (low for the output voltage of 0.5% or so), the best products of the ripple and noise voltage is also dozens of mV; and linear power supply adjuster tube working in the linear state, no ripple voltage, the output noise voltage is also smaller, the unit is μV.
Ripple and noise causes
Switching power supply output is not pure DC voltage, some AC components, which is caused by ripple and noise. Ripple is the fluctuation of the output DC voltage, and the switching action of the switching power supply. Each on and off process, electrical energy from the input is "pumped" to the output, the formation of a charging and discharging process, resulting in fluctuations in the output voltage, fluctuations in the same frequency and switching frequency. Ripple voltage is the peak-to-peak value between the peaks and valleys of the ripple, and its size is related to the capacity and quality of the input and output capacitors of the switching power supply.
There are two causes of noise, one is generated by the switching power supply itself; the other is the interference of external electromagnetic fields (EMI), which can enter the switching power supply through radiation or be fed into the switching power supply through the power cord.
The noise generated by the switching power supply itself is a high-frequency burst, caused by the sharp pulses occurring in the switch on and off moment, also known as switching noise. The frequency of the noise burst is much higher than the switching frequency, and the noise voltage is its peak-to-peak value. The amplitude of the noise voltage is largely related to the topology of the switching power supply, the parasitic states in the circuit and the design of the PCB.
Using an oscilloscope, you can see the waveforms of the ripple and the noise. The frequency of the ripple is the same as the frequency of the switching tube, while the frequency of the noise is twice that of the switching tube. The sum of the peak-to-peak value of the ripple voltage and the peak-to-peak value of the noise voltage is the ripple and noise voltage in mVp-p.
