Ripple, harmonic and noise in power supply
Ripple: A clutter signal with periodic and random components attached to the DC level. The peak value of AC voltage in the output voltage under rated output voltage and current. In a narrow sense, ripple voltage refers to the power frequency AC component contained in the output DC voltage.
Ripple generation: We usually use linear power supply and switching power supply in our products. The output DC voltage is a fixed value, which is obtained by rectifying, filtering and stabilizing AC voltage. Because the filter is not clean, the DC voltage contains AC component, which produces ripple. Ripple is a complex clutter signal, which is a periodic signal around the fluctuation of output DC voltage, but the period and amplitude are not fixed value, and change with time.
Harm of ripple: high ripple voltage may cause harmonic and modulation of electronic products, interfere with the normal working state; lead to lower power efficiency; affect the logic relationship of digital circuits; interfere with the normal transmission of signals and so on. Strong ripple will generate surge voltage or current, which may burn down electrical equipment.
Harmonic: refers to the electric quantity contained in the current which is an integer multiple of the fundamental frequency. Generally speaking, it refers to the Fourier series decomposition of periodic non-sinusoidal electric quantity, and the electric quantity generated by the other current which is larger than the fundamental frequency. Generally speaking, because the effective component of AC network is a single frequency of power frequency, any component different from power frequency can be called harmonic.
The reason of harmonic generation: Because the sinusoidal voltage is pressurized on the non-linear load, when the current flows through the load, it does not have a linear relationship with the added voltage, and the fundamental current distortion will form a non-sinusoidal current, that is, harmonic generation in the circuit. The main non-linear loads are UPS, switching power supply, rectifier, frequency converter, inverters and so on.
Noise: For the nominal noise in electronic circuits, it can be generally considered that it is a general term for all signals other than the target signal. At first, people called the electronic signals that caused the noise of such audio equipment as radio as noise. However, the consequences of some non-purpose electronic signals on electronic circuits are not all related to sound, so the concept of noise has been gradually expanded. For example, the electronic signals that cause white spot streaks on the screen are also called noise. It can be said that all signals in the circuit, except for the purpose signal, regardless of whether it affects the circuit or not, can be called noise. For example, ripple or self-excited oscillation in the power supply voltage can have a negative impact on the circuit, make the audio device produce alternating sound or cause circuit malfunction, but sometimes it may not lead to the above consequences. For this kind of ripple or oscillation, it should be called a kind of noise of circuit. There is a certain frequency of radio wave signal. For the receiver that needs to receive this signal, it is a normal purpose signal, while for the other receiver it is a non-purpose signal, that is, noise. The term interference is often used in electronics, sometimes confused with the concept of noise. In fact, it is different. Noise is an electronic signal, and interference refers to an effect, which is a kind of adverse reaction caused by noise to the circuit. There is noise in the circuit, but there is not always interference. In digital circuits. Often, it can be observed by an oscilloscope that there are some small spikes mixed with the normal pulse signal, which is not expected, but a kind of noise. However, due to the characteristics of the circuit, these small spike pulses are not so confusing as to affect the logic of the digital circuit, so it can be considered that there is no interference.
When a noise voltage is large enough to disturb the circuit, the noise voltage is called the interference voltage. When a circuit or a device can maintain the maximum noise voltage when it works normally, it is called the anti-interference tolerance or anti-interference degree of the circuit or device. Generally speaking, noise is difficult to eliminate, but we can try to reduce the intensity of noise or improve the immunity of circuit, so that noise does not interfere.
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