This page will concerns the ripple and noise of AC-DC power adapters or switching power supplies. It describes basic information on ripple and noise.
What is ripple?
Ripple and noise voltage is the alternating current voltage superimposed on the output voltage. Ripple is a phenomenon caused by voltage fluctuations in the DC stabilized power supply because the DC stabilized power supply is generally formed by the AC power supply through rectification, voltage regulation, filtering and other links. Due to incomplete filtering, residual AC components will inevitably be more or less in the DC stabilized amount with some AC components. This superimposed on the DC stabilized amount of the AC component is called ripple. The ripple component is more complex. Its form is generally higher than the frequency of the sine wave-like harmonics. Another is a very narrow width of the pulse wave. Generally, we see the ripple in the form of the following figure, a bit like a sawtooth wave.
From this, we know that the switching power supply's output is not pure DC voltage. There are some AC components which are caused by ripple and noise. Ripple is the output DC voltage fluctuation and is related to the switching power supply's switching action. For each on/off process, the electrical energy is "pumped" from the input to the output, forming a charging and discharging process, which causes the output voltage to fluctuate at the same frequency as the switch. The ripple voltage is the peak between the crest and trough of the ripple.
What is noise?
There are two causes of noise. The switching power supply generates one; the other is the external electromagnetic field (EMI) interference, which can enter the switching power supply through radiation.
Switch generally uses bipolar transistors or mosfets. No matter which, there will be a rise time and a fall time when it is on and off. These two types of noise are generally called high-frequency noise, and the amplitude is usually much larger than the ripple. The frequency of the noise burst is much higher than the switching frequency, and the noise voltage is its peak-to-peak value.
When testing a power supply, ripple and noise are generally not separated intentionally. What is measured is the combined interference of ripple and noise, which is expressed as peak-to-peak voltage.
Impacts of Ripple Noise
1. tends to produce harmonics on the appliance, and harmonics can produce more harm.
2. Reduces the efficiency of the power supply.
3. Stronger ripple or cause the generation of inrush voltage or current, resulting in burning power-using devices.
4. can interfere with the logic relationship of digital circuits and affect normal operation.
5. will bring noise interference, making the imaging and audio equipment can not work properly.
In summary, ripple noise has significant harm to the power supply and the electrical equipment connected to it. Therefore, it is very important to reduce ripple noise to the lowest level during the power supply design and manufacturing process.
