What are ripples, harmonics and noise?

What is ripple?

Ripple is a phenomenon caused by fluctuations in voltage of a DC power supply, since a DC power supply is usually formed by an AC power supply by rectifying and stabilizing voltage. The stability of direct current is called ripple.

Wave Generation

Ripple is a phenomenon caused by fluctuations in voltage of a DC power supply, since a DC power supply is usually formed by an AC power supply by rectifying and stabilizing voltage. The stability of direct current is called ripple. The composition of ripple is more complex, and its shape is generally a sinusoidal harmonic with a frequency higher than mains frequency (50 Hz in China), and other is a pulse wave with a narrow width. For different cases, requirements for pulsation are different.

Ripple damage

1. It is easy to generate harmonics on electrical appliances, and harmonics cause more harm;

2. Reduce efficiency of power supply;

3. Strong ripples will cause a surge in voltage or current, which will lead to burnout of electrical appliances;

4. This will affect logical relationship of digital circuit and affect its normal operation;

5. This will cause noise interference, so image processing equipment and audio equipment cannot operate normally.

In short, they are harmful when they appear where we do not need them, and we need to avoid them. There are many ways to suppress and eliminate harmonics and ripple, but it is difficult to completely eliminate them, we can only control them within acceptable limits without affecting environment and equipment.

What are harmonics?

Harmony literally means "many parts", and harmony means that several parts are in harmony. Wave refers to waveform (Wave). To describe it together, it is a waveform made up of many kinds of waves.

It can be learned from advanced math analysis that any periodic signal can be decomposed into a fundamental frequency sine wave plus many higher frequency sinusoids, with higher frequency being an integer multiple of fundamental frequency (N, can only be an integer), DC component is called 0 th harmonic, fundamental wave is called 1st harmonic, and waveform above second is called higher harmonic for odd harmonics. For example, a signal with a fundamental frequency of 200 Hz has a fundamental waveform of 200 Hz. When its waveform is not a pure sine wave, there will be distortion. The waveform above 200 Hz is called high order harmonic, and 400 Hz is called second harmonic. harmonic. , 600Hz is third harmonic and so on. The figure below visually synthesizes this waveform, which consists of a 200 Hz sinusoidal fundamental wave and 2-5 higher harmonics.

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Causes of harmonics

The reason for generating harmonics: Since a sinusoidal voltage is applied to a non-linear load, when current flows through load, it does not have a linear relationship with applied voltage, and main current is distorted, forming a non-linear - sinusoidal current, that is, harmonics are generated in circuit. The main non-linear loads are UPS, switching power supply, rectifier, frequency converter, inverter, etc.

What is noise?

Noise. For nominal noise in electronic circuits, one can usually think of it as a generic term for all signals other than target signal. At first, people referred to electronic signals that cause noise produced by audio equipment such as radios as noise. However, consequences of some non-target electronic signals in electronic circuits are not all related to sound, so people have gradually expanded concept of noise.

For example, those electronic signals that cause white streaks on screen are also called noise. We can say that all signals in circuit, except for target signal, regardless of whether it affects circuit or not, can be called noise. For example, ripples or self-oscillations in power supply voltage can adversely affect a circuit, causing audio device hum or circuit malfunction, but sometimes may not cause above effects. This kind of ripple or oscillation should be called a kind of circuit noise. There is also a radio wave signal of a certain frequency. For a receiver that needs to receive this signal, this is a normal signal, and for another receiver it is a non-purpose signal, that is, noise. The term interference is often used in electronics and is sometimes confused with concept of noise, in fact there is a difference. Noise is an electronic signal, and interference refers to an effect that is an unfavorable reaction to a circuit due to noise. Although there is noise in circuit, there is not necessarily interference. in digital circuits. With an oscilloscope, you can often observe that some small spikes mixed with a normal pulse signal are not expected, but are a kind of noise. However, due to nature of circuit, these small spikes will not affect logic of digital circuit and will not cause confusion, so it can be assumed that there is no interference.

When noise voltage is high enough to disrupt circuit, noise voltage is called interference voltage. And a circuit or device, when it can maintain normal operation, maximum added noise voltage is called noise immunity or noise immunity of circuit or device. Generally speaking, noise is difficult to eliminate, but one can try to reduce intensity of noise or increase noise immunity of circuit so that noise does not interfere.